U.S. patent application number 15/578259 was filed with the patent office on 2018-06-21 for metal alloy composites.
This patent application is currently assigned to YADA RESEARCH AND DEVELOPMENT CO. LTD.. The applicant listed for this patent is YADA RESEARCH AND DEVELOPMENT CO. LTD.. Invention is credited to Chia-Han HO, Song-Jeng HUANG, Reshef TENNE.
Application Number | 20180171435 15/578259 |
Document ID | / |
Family ID | 58400810 |
Filed Date | 2018-06-21 |
United States Patent
Application |
20180171435 |
Kind Code |
A1 |
TENNE; Reshef ; et
al. |
June 21, 2018 |
METAL ALLOY COMPOSITES
Abstract
This invention relates to metal composites and to metal-alloy
composites. Metal-alloy composites of this invention comprise a
metal alloy and layered inorganic nanostructures or nanoparticles
such as nanotubes, nanoscrolls, spherical or quasi-spherical
nanoparticles, nano-platelets or combinations thereof. Methods of
producing the metal composites and the metal-alloy composites are
demonstrated. The layered inorganic nanostructure serves as a
strengthening phase. The layered inorganic nanostructure provides
reinforcement to the metal alloy.
Inventors: |
TENNE; Reshef; (Rehovot,
IL) ; HUANG; Song-Jeng; (Taipei, TW) ; HO;
Chia-Han; (Taipei, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
YADA RESEARCH AND DEVELOPMENT CO. LTD. |
Rehovot |
|
IL |
|
|
Assignee: |
YADA RESEARCH AND DEVELOPMENT CO.
LTD.
Rehovot
IL
|
Family ID: |
58400810 |
Appl. No.: |
15/578259 |
Filed: |
June 1, 2016 |
PCT Filed: |
June 1, 2016 |
PCT NO: |
PCT/IL2016/050563 |
371 Date: |
November 30, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62169094 |
Jun 1, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 23/00 20130101;
C22C 1/00 20130101; C22C 23/02 20130101; C22F 1/06 20130101; C22C
2001/1052 20130101; C22C 1/10 20130101; C22C 32/0089 20130101; C22C
1/1036 20130101 |
International
Class: |
C22C 1/10 20060101
C22C001/10; C22C 23/02 20060101 C22C023/02; C22C 32/00 20060101
C22C032/00; C22F 1/06 20060101 C22F001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2015 |
TW |
104143509 |
Claims
1. A metal or a metal-alloy composite comprising: a. metal or a
metal alloy; and b. inorganic layered nanostructured material,
wherein the inorganic layered nanostructured material does not
comprise carbon.
2. (canceled)
3. The metal-alloy composite of claim 1, wherein said metal alloy
composite comprises Mg, Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn, Ag, Au or a
combination thereof.
4. The metal-alloy composite of claim 3, wherein the base metal in
said metal alloy is Mg.
5. The metal-alloy composite of claim 3, wherein the base metal in
said metal alloy is Fe, Cu, Al, Ti, Zn, Ni, Hg.
6. The metal-alloy composite of claim 1, wherein said metal alloy
comprises one or more secondary metals.
7. The metal-alloy composite of claim 6, wherein said secondary
metal(s) in said metal alloy comprises Al, Zn, Mn or a combination
thereof.
8. The metal-alloy composite of claim 6, wherein said secondary
metal(s) in said metal alloy comprises Zn, Al, Cu, Mg, Mn, Sn, Sb,
Ag, Au, Pt, Pd, In, Zr, Ni, Fe, C, Si, Ti, Pb, Be, Y, Cc, Nd, Ca,
Os, As, Ba, B, Cr, Co, Ga, Ge, Li, Rh, Ru, Se, Sr, W, Na, Pt, Cd,
Bi, or a combination thereof.
9. The composite of claim 1, wherein said layered inorganic
nanostructured material is a spherical nanoparticle, a
quasi-spherical nanoparticle, a nanotube, a nanoscroll, a
nano-platelet or a combination thereof.
10. The composite of claim 1, wherein said inorganic layered
nanostructured material comprises WS.sub.2, MoS.sub.2, or a
combination thereof.
11. The metal alloy composite material of claim 9, wherein the
sulfur-containing compound is 2H-phase WS.sub.2.
12. The composite material of claim 1, wherein the concentration of
said layered inorganic nanostructured material in said composite
ranges between 0.001 wt % to 15 wt %.
13. The composite of claim 12, wherein the concentration of said
layered inorganic nanostructured material in said composite ranges
between 0.001 wt % and 1 wt %.
14. The metal-alloy composite of claim 1, wherein the % increase in
fracture toughness of said composite with respect to an alloy
without the inorganic layered structure ranges between 250% and
300%.
15. The metal-alloy composite of claim 1, wherein the % increase in
yield strength of said composite with respect to an alloy without
the inorganic layered structure ranges between 15% and 20%.
16. The metal-alloy composite of claim 1, wherein the % increase in
ultimate tensile strength of said composite with respect to an
alloy without the inorganic layered structure ranges between 45%
and 70%.
17. The metal-alloy composite of claim 1, wherein the elongation of
said composite with respect to an alloy without the inorganic
layered structure ranges between 140% and 400%.
18. The metal-alloy composite of claim 1, wherein the size of the
grains of said composite ranges between 50 .mu.m-100 .mu.m.
19. A method for producing a metal or a metal-alloy composite
comprising: metal or metal alloy; and layered inorganic
nanostructures; wherein said method comprises: a. placing said
metal or metal alloy and said inorganic layered nanostructured
material in a crucible; b. heating said metal or metal alloy and
said inorganic layered nanostructured material in said crucible to
a first temperature, forming a melt; c. stirring said melt of said
metal or metal alloy and said inorganic layered nanostructured
material in said crucible; d. bringing gas into contact with said
melt in said crucible; e. optionally heating said melt in said
crucible to a second temperature; f. optionally heating said melt
in said crucible to a third temperature; g. pouring said melt into
a mold; h. cooling said melt; thus forming a solid metal or
metal-alloy composite.
20. (canceled)
21. The method of claim 19, wherein the order of steps b, c, and d
is switched or wherein steps b; c, and d are conducted in parallel
or at least partially overlap in time.
22. The method of claim 19, wherein said first temperature is
380-420.degree. C., said second temperature is 580-620.degree. C.
and said third temperature is 680-720.degree. C.
23. The method of claim 19, wherein said gas is selected from the
group consisting of CO.sub.2, SF.sub.6, N.sub.2, Ar or a
combination thereof.
24. The method of claim 19, wherein said melt is kept at said first
temperature and optionally at said second temperature and
optionally at said third temperature for a period of time ranging
between 10 min-20 min.
25. The method of claim 19, wherein said heating is conducted in a
resistance-heating furnace.
26. The method of claim 19, wherein said stirring is conducted
using a stirrer comprising a vane, a blade, a rod, a screw or a
combination thereof.
27. A method for producing a metal or a metal-alloy composite
comprising: metal or metal alloy; and layered inorganic
nanostructures; wherein said method comprises: heating a metal or a
metal alloy to form a melt or a metal solution; adding a layered
inorganic nanostructure into the metal or metal solution; cooling
down the metal or metal solution containing the metal or metal
alloy and the layered inorganic nanostructures to form a composite
material; and optionally performing a solid solution treatment to
the composite material.
28. (canceled)
29. The method of claim 27, wherein the metal alloy is a
magnesium-based alloy or an aluminum-based alloy.
30. The method of claim 27, wherein the layered inorganic
nanostructure is a sulfur-containing compound.
31. The method of claim 30, wherein the sulfur-containing compound
comprises tungsten disulfide (WS.sub.2), molybdenum disulfide
(MoS.sub.2) or a combination thereof.
32. The method of claim 27, further comprising introducing a
protective gas when heating the metal or the metal alloy.
33. The method of claim 32, wherein introducing the protective gas
comprises introducing helium (He), argon (Ar), nitrogen (N.sub.2),
sulfur hexafluoride (SF.sub.6), carbon dioxide (CO.sub.2) or a
combination thereof.
34. The method of claim 32, wherein protective gas introduction is
stopped after holding a temperature of between 600.degree. C. and
800.degree. C. for 1 min to 2 hour.
35. A metal composite or a metal-alloy composite comprising: a.
metal or metal alloy; and b. inorganic layered nanostructured
material. wherein said metal composite or metal-alloy composite is
produced by the method described in claim 19.
36. A metal composite or a metal-alloy composite comprising: a.
metal or metal alloy; and b. inorganic layered nanostructured
material. wherein said metal composite or metal-alloy composite is
produce by the method described in claim 27.
Description
FIELD OF THE INVENTION
[0001] This invention relates to metal composites and metal-alloy
composites. Metal-alloy composites of this invention comprise metal
alloy and layered inorganic nanostructures such as nanotubes and
spherical nanoparticles. The layered inorganic nanostructures
provide reinforcement to the metal alloy. Methods of producing the
metal alloy composites are demonstrated.
BACKGROUND OF THE INVENTION
[0002] Fuel saving considerations and new technological
developments drive metal alloys strongly into the realm of everyday
life in the automotive, aerospace, medical technologies and other
industries. However, the process engineering of such alloys is
often times compromised by their relatively poor mechanical
properties.
[0003] For example, magnesium (Mg) alloys are gaining more
recognition as a lightest structural material for light-weight
applications, due to their low density and high stiffness-to-weight
ratio. In spite of this, Mg alloys have not been used for critical
mechanical applications mainly due to their inferior mechanical
properties compared to other engineering materials such as steel
and aluminum. Hence, attempts have been made to fabricate Mg-based
metal-matrix composites (Mg MMC's) by different methods in order to
obtain light-weight Mg MMC's with enhanced mechanical
properties.
[0004] In recent years, ceramic nanoparticles, such as SiC and
Al.sub.2O.sub.3 nanoparticles have been used to reinforce different
metallic materials to form metal matrix composites. The proposed
mechanisms for the strengthened metal-matrix composites (MMC's)
were thermal expansion mismatch, Orowan looping, Hall-Petch
relation and the shear-lag model. The thermal expansion mismatch
between the nanoparticles and the matrix results in increased
dislocation density, increasing thereby the yield strength of the
nano-MMC's. The nanoparticles in the matrix can impede dislocation
motion during tensile testing. They can also lead to dislocation
bowing, and subsequent formation of dislocation loops around the
nanoparticle, i.e. the Orowan looping mechanism. Orowan looping
mechanism is more pronounced in MMC's reinforced with ceramic
nanoparticles of low aspect ratio, i.e. close to unity. According
to the Orowan mechanism, finer particles are more efficient in
improving the mechanical properties of the composite.
[0005] The introduction of nanomaterials into the metal matrix to
form composites is rather difficult due to the harsh manufacturing
conditions employed for processing the metal composites. The main
challenges for processing nano-MMCs are: a. reaching homogeneous
dispersion of the reinforcing nanomaterials in the metal matrix; b.
the formation of sufficiently strong interfacial bonding; and c.
retention of the chemical and structural constancy of the
nanomaterials, and in particular preventing its oxidation.
[0006] The addition of nanoparticles with high aspect ratio can
enhance the mechanical properties of the MMC's without resorting to
heavy machining which induce substantial plastic deformation. Thus
MMC's can lead also to improved stress corrosion resistance of the
Mg-alloys. The stiffening and strengthening effects of such
nanofillers depends greatly on achieving effective stress-transfer
across the metal matrix-nanofiller interface. The aspect ratio,
homogeneous dispersion of nanofillers in the matrix, and the
formation of interfacial products also govern the load transfer
efficiency of nanomaterials in MMC.
[0007] Carbon nanotubes (CNT's) tend to tangle with each other due
to the van der Walls force and the mutual interaction through the
.pi. electrons, the so-called .pi.-.pi. interaction. Since carbon
becomes reactive with numerous metals at elevated temperatures, the
structural integrity of CNT's is impaired under high-temperature
processing and high pressure conditions. Besides, the chemical
reaction between CNTs and the molten metal leads to the formation
of interfacial products, like carbides, causing structural damage
of the nanomaterials. Synthesizing carbide films, such as
Al.sub.2MgC.sub.2 at the interfaces is vital for producing CNTs
metal composites having high strength and acceptable ductility.
Mg-rich alloy (AZ61) MMC was reinforced by CNTs. The CNTs were
first dispersed in isopropyl alcohol (IPA) using zwitterionic
surfactant. Spark plasma sintering (SPS) of the MMC produced the
Al.sub.2MgC.sub.2 phase at the interface between the CNT
agglomerates and the Mg-alloy. The fabricated composite showed
increased elongation compared with the pure metal alloy. In another
series of experiments, powder metallurgy (PM) was used for the
addition of CNTs to AZ61 Mg MMCs. Like the previous study, the
nanotubes were dispersed in the AZ61 alloy with the help of an
IPA-based zwitterionic surfactant. The yield strength increased by
21.1, 23.4, and 28.5 MPa, respectively, compared with pristine AZ61
(about 225 MPa). Contrarily, water based (CNT) solutions produces
substantial amounts of MgO which reduced the ductility of the
Mg-alloy. Therefore, employing IPA-based solution could prevent
producing excess amount of MgO during the MMCs processing and was
beneficial to the mechanical properties of the MMC's.
[0008] Powder metallurgy (PM) technique is a versatile process for
manufacturing nano-MMC's due to its simplicity, flexibility and
net-shape capability. The main drawback of the PM process is the
high cost of the raw material powders. The mechanical properties of
nano-MMCs, such as hardness and yield strength, can be increased to
some extent by PM accompanied by hot extrusion.
[0009] Extruded AZ91D Mg MMC's compounded with 1, 3, 5 wt. % CNT's
exhibited increased yield strength of 27%, 22.4% and 19.4% compared
to that of extruded AZ91D, respectively. However, the ductility of
the MMC's deteriorated with increasing content of the CNT's. Hot
extruded pure Mg MMC's reinforced by 0.3 and 1.3 wt % CNT's have
shown a 1.5% and 11.1% increase in the yield strength compared to
that of pure Mg (126 MPa), respectively.
[0010] AZ61 nano-MMCs reinforced by 0.5 wt %, 1 wt %, 2 wt % and 4
wt % CNT's which was processed by mechanical ball milling, cold
pressing and subsequently hot extrusion (without sintering step),
exhibited 27%, 21%, 34% and 34% reduction in the wear rates as
compared to the alloy containing no CNT (AZ61). Tribological tests
of Mg/micro SiC/MWCNTs MMC's showed better wear resistance than
that of monolithic Mg and Mg/micro SiC MMC's under high load of 40
N and high sliding velocity of 3.5 m/s. The main penalty in using
such endergonic techniques is that they induce appreciable plastic
deformations in the solid and consequently expedite severe stress
corrosion.
[0011] In view of their potential applications, there is a need to
produce stable and robust metal alloy composites with enhanced
mechanical properties. There is a need to explore the potential
contribution of novel nanostructures to such metal alloy
composites.
SUMMARY OF THE INVENTION
[0012] In one embodiment, this invention provides a metal alloy
composite material improved in mechanical strength as well as
elongation and a method for making the same.
[0013] In accordance with some embodiments of the present
invention, a method for making a metal alloy composite material is
provided. The method includes: providing a metal alloy matrix and
reinforcement; heating the metal alloy matrix to form a metal
solution; adding the reinforcement into the metal solution; cooling
down the metal solution containing the reinforcement to form a
composite material; and optionally performing a solid solution heat
treatment to the composite material. The metal alloy matrix is a
magnesium-based alloy or an aluminum-based alloy in one embodiment,
and the reinforcement is a sulfur-containing compound in one
embodiment.
[0014] In accordance with some embodiments of the present
invention, a metal alloy composite material is provided. The metal
alloy composite material includes a metal alloy matrix and a
reinforcement strengthening phase, wherein in some embodiments, the
metal alloy matrix is a magnesium-based alloy or an aluminum-based
alloy and the strengthening phase is a sulfur-containing compound
in some embodiments.
[0015] Poor mechanical properties of metal alloys such as Mg alloys
are an obstacle to their use in new technologies. In order to
address this issue, metal-matrix composites (MMC's) of Mg-alloys
have been investigated. In one embodiment, small amounts of
inorganic layered nanoparticles such as nanotubes were incorporated
into Mg alloys and provided enhanced mechanical properties.
[0016] In one embodiment, up to 1 wt % of WS.sub.2 nanotubes were
mixed with Mg-alloy (AZ31) using a melt-stirring process at a
temperature of above 700.degree. C. The new MMC nano-composites
exhibit superior mechanical properties compared with the pristine
alloy. Metallographic investigation demonstrated that the average
grain size has been reduced in inverse proportion to the added
amounts of nanotubes up to 1 wt %. Physical considerations suggest
that the main mechanism responsible for the reinforcement effect
lies in the mismatch between the thermal expansion coefficients of
the metal and the nanotubes. This mismatch induced large density of
dislocations in the grain boundaries in the vicinity of the
nanotube-matrix interface, which obstruct the crack
propagation.
[0017] In one embodiment, this invention provides a metal-alloy
composite comprising: [0018] metal alloy; and [0019] inorganic
layered nanostructured material.
[0020] In one embodiment, this invention provides a metal composite
comprising: [0021] a metal; and [0022] inorganic layered
nanostructured material.
[0023] In one embodiment, the metal alloy matrix comprises Mg, Fe,
Cu, Al, Ti, Zn, Ni, Hg, Mn, Ag, Au or a combination thereof.
[0024] In one embodiment, the base metal in said metal alloy is Mg.
In one embodiment, the base metal in said metal alloy is Fe, Cu,
Al, Ti, Zn, Ni, Mn.
[0025] In one embodiment, the metal alloy comprises one or more
secondary metals. In one embodiment, the secondary metal(s) in said
metal alloy comprises Zn, Al, Cu, Mg, Mn, Sn, Sb, Ag, Au, Pt, Pd,
In, Zr, Ni, Fe, C, Si, Ti, Pb, Be, Y, Ce, Nd, Ca, Os, As, Ba, B,
Cr, Co, Ga, Ge, Li, Rh, Ru, Se, Sr, W, Na, Pt, Cd, Bi, Si or a
combination thereof.
[0026] In one embodiment, the layered inorganic nanostructured
material is a spherical or a quasi-spherical nanoparticle, a
nanotube, a nanoscroll, a sheet, a distorted sheet, a nanoplatelet
or a combination thereof.
[0027] In one embodiment, the layered inorganic nanostructured
material comprises a sulfur-containing compound.
[0028] In one embodiment, the layered inorganic nanostructured
material comprises WS.sub.2, MoS.sub.2, or a combination thereof.
In one embodiment, the sulfur-containing compound is 2H-phase
WS.sub.2.
[0029] In one embodiment, the concentration of said layered
inorganic nanostructured material in said composite ranges between
0.001 wt % to 15 wt %. In one embodiment, the concentration of the
layered inorganic nanostructured material in said composite ranges
between 0.001% and 1%.
[0030] In one embodiment, the % increase in yield strength of the
composite with respect to an alloy without the inorganic layered
nanostructure ranges between 15% and 20%. In one embodiment, the %
increase in ultimate tensile strength of the composite with respect
to an alloy without the inorganic layered nanostructure ranges
between 45% and 70%. In one embodiment, the % elongation of the
composite with respect to an alloy without the inorganic layered
nanostructure ranges between 140% and 400%.
[0031] In one embodiment, the size of the grains of the composite
ranges between 50 .mu.m-100 .mu.m.
[0032] In one embodiment, the fracture toughness of the composite
is increased with respect to an alloy without the inorganic layered
structure. In one embodiment, the % increase of the fracture
toughness of the composite with respect to an alloy without the
inorganic layered structure is 272%. In one embodiment, the %
increase of the fracture toughness of the composite with respect to
an alloy without the inorganic layered structure ranges between
250% and 300%.
[0033] In one embodiment, composites of the invention possess
enhanced properties with respect to the metal alloy without the
inorganic layered nanostructure. In one embodiment, the enhanced
property is reduced stress-corrosion.
[0034] In one embodiment, this invention provides a method for
producing a metal-alloy composite comprising: [0035] metal alloy;
and [0036] layered inorganic nanostructures; wherein the method
comprises: [0037] a. placing the metal alloy and the inorganic
layered nanostructured material in a crucible; [0038] b. heating
the metal alloy and the inorganic layered nanostructured material
in the crucible to a first temperature, forming a melt; [0039] c.
stirring the melt of the metal alloy and the inorganic layered
nanostructured material in the crucible; [0040] d. bringing gas
into contact with the melt in the crucible; [0041] e. optionally
heating the melt in the crucible to a second temperature; [0042] f.
optionally heating the melt in the crucible to a third temperature;
[0043] g. pouring the melt into a mold; [0044] h. cooling the melt,
thus forming a solid metal-alloy composite.
[0045] In one embodiment, this invention provides a method for
producing a metal composite comprising: [0046] a metal; and [0047]
layered inorganic nanostructures; wherein said method comprises:
[0048] a. placing said metal and said inorganic layered
nanostructured material in a crucible; [0049] b. heating said metal
and said inorganic layered nanostructured material in said crucible
to a first temperature, forming a melt; [0050] c. stirring said
melt of said metal and said inorganic layered nanostructured
material in said crucible; [0051] d. bringing gas into contact with
said melt in said crucible; [0052] e. optionally heating said melt
in said crucible to a second temperature; [0053] f. optionally
heating said melt in said crucible to a third temperature; [0054]
g. pouring said melt into a mold; [0055] h. cooling said melt, thus
forming a solid metal composite.
[0056] In one embodiment, the order of steps b, c, and d or any
combination thereof is switched or reversed. In one embodiment,
steps b, c, and d or any combination thereof are conducted in
parallel, or at least partially overlap in time.
[0057] In one embodiment, the first temperature is 380-420.degree.
C., the second temperature is 580-620.degree. C. and the third
temperature is 680-720.degree. C.
[0058] In one embodiment, the first temperature, optionally the
second temperature, optionally the third temperature or a
combination thereof exceeds 700.degree. C.
[0059] In one embodiment, the gas is selected from the group
consisting of CO.sub.2, SF.sub.6 or a combination thereof.
[0060] In one embodiment, the melt is kept at the first temperature
and optionally at the second temperature and optionally at the
third temperature for a period of time ranging between 10 min-20
min.
[0061] In one embodiment, the heating is conducted in a
resistance-heating furnace.
[0062] In one embodiment, the stirring is conducted using a
stirrer. In one embodiment, the stirrer comprises a vane, a blade,
a rod, a screw or a combination thereof.
[0063] In one embodiment this invention provides a method for
producing a metal-alloy composite comprising: [0064] metal alloy;
and [0065] layered inorganic nanostructures; wherein said method
comprises: [0066] heating a metal alloy to form a metal solution;
[0067] adding a layered inorganic nanostructure into the metal
solution; [0068] cooling down the metal solution containing the
metal alloy and the layered inorganic nano structures to form a
composite material; and [0069] optionally performing a solid
solution treatment to the composite material.
[0070] In one embodiment, this invention provides a method for
producing a metal composite comprising: [0071] a metal; and [0072]
layered inorganic nanostructures; wherein said method comprises:
[0073] heating a metal to form a melt; [0074] adding a layered
inorganic nanostructure into the metal melt; [0075] cooling down
the metal melt containing the metal and the layered inorganic
nanostructures to form a composite material; and [0076] optionally
performing a solid solution treatment to the composite
material.
[0077] In one embodiment, the metal alloy is a magnesium-based
alloy or an aluminum-based alloy. In one embodiment, the layered
inorganic nanostructure is a sulfur-containing compound. In one
embodiment, the sulfur-containing compound comprises tungsten
disulfide (WS.sub.2), molybdenum disulfide (MoS.sub.2) or a
combination thereof.
[0078] In one embodiment, the method further comprises introducing
a protective gas when heating the metal alloy matrix.
[0079] In one embodiment, introducing the protective gas comprises
introducing helium (He), argon (Ar), nitrogen (N.sub.2), sulfur
hexafluoride (SF.sub.6), carbon dioxide (CO.sub.2) or a combination
thereof.
[0080] In one embodiment, the protective gas introduction is
stopped after holding a temperature of between 600.degree. C. and
800.degree. C. for 1 min to 2 hour.
[0081] In one embodiment, this invention provides a metal composite
or a metal-alloy composite comprising: [0082] metal or metal alloy;
and [0083] inorganic layered nanostructured material; [0084]
wherein the metal composite or the metal-alloy composite is
produced by any of the methods described herein above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0085] The subject matter regarded as the invention is particularly
pointed out and distinctly claimed in the concluding portion of the
specification. The invention, however, both as to organization and
method of operation, together with objects, features, and
advantages thereof, may best be understood by reference to the
following detailed description when read with the accompanying
drawings in which:
[0086] FIGS. 1A-1B. FIG. 1A shows SEM image of an assortment of
WS.sub.2 nanotubes; FIG. 1B shows TEM image of a single WS.sub.2
nanotube, scale bar is 5 nm.
[0087] FIGS. 2A-2C. FIG. 2A shows Schematic rendering of the
reactor used for the fabrication of the Mg-MMC with different
concentrations of the WS.sub.2 nanotubes; FIG. 2B shows The
stainless steel mold used for melting the Mg-alloy and mixing with
the WS.sub.2 nanotubes; FIG. 2C shows Optical micrographs of four
of the Mg-MMC ingots prepared at different temperatures for an
embodiment of the present study. From right to left: 650.degree.
C.; 680.degree. C.; 700.degree. C. and 750.degree. C. One notices
that the ingots prepared below 700.degree. C. do not appear to be
uniform.
[0088] FIG. 3 is a plot showing XRD patterns of the AZ31INT0.5-1
sample and a pristine Mg alloy.
[0089] FIG. 4 is Stress-strain curve (tensile test) of the pure
Mg-AZ31 alloy and the Mg MMC with 1 wt % nanotubes (AZ31INT1-x;
x=1-3). Notwithstanding the variation in the results, the Mg-MMC
with 1 wt % nanotubes exhibit appreciable improvements in the
mechanical properties compared with the pristine alloy.
[0090] FIG. 5 is a summary of the mechanical testing of the
different Mg-alloy samples.
[0091] FIG. 6 shows metallography of the pure Mg alloy and the
different Mg alloys formulated with 1 wt % INT-WS.sub.2.
[0092] FIGS. 7A-7B. FIG. 7A shows Comparison between the grain
sizes, as concluded from the metallographic analysis, for the
pristine AZ31 Mg alloy and for different samples of the Mg MMC with
1 wt % INT-WS.sub.2. Note that the grain sizes of the different
MMC's are quite similar. Error bars for the results of the analysis
are included as well; FIG. 7B shows Comparison between the grain
sizes of the pristine AZ31 Mg alloy and the MMC's with 0.5 and 1 wt
% of WS.sub.2 nanotubes. The different sizes of the error bars
represent the statistical variation of the grain sizes in the
analyzed samples. Note that the error bars are diminishing with the
addition of larger amounts of the nanotubes.
[0093] FIG. 8 illustrates an exemplary flow chart of a method for
making a metal alloy composite material.
[0094] FIG. 9 illustrates an exemplary cross-sectional view of a
furnace for making a metal alloy composite material.
[0095] FIGS. 10A through 10C illustrate x-ray diffraction patterns
of metal alloy composite materials.
[0096] FIGS. 11A through 11C illustrate x-ray diffraction patterns
of metal alloy composite materials.
[0097] FIGS. 12A through 12F illustrate metallographic photos of
metal alloy composite materials.
[0098] FIGS. 13A through 13F illustrate metallographic photos of
metal alloy composite materials.
[0099] It will be appreciated that for simplicity and clarity of
illustration, elements shown in the figures have not necessarily
been drawn to scale. For example, the dimensions of some of the
elements may be exaggerated relative to other elements for clarity.
Further, where considered appropriate, reference numerals may be
repeated among the figures to indicate corresponding or analogous
elements.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0100] In the following detailed description, numerous specific
details are set forth in order to provide a thorough understanding
of the invention. However, it will be understood by those skilled
in the art that the present invention may be practiced without
these specific details. In other instances, well-known methods,
procedures, and components have not been described in detail so as
not to obscure the present invention.
[0101] Introducing nanotubes into molten alloys at high
temperatures is extremely challenging and has not been attempted
before. The success of such process depends on issues of reactivity
of the metal with components of the nanotubes, e.g. sulfides.
Accordingly, it was not predicted that metal alloys could be
reinforced by e.g. WS.sub.2 or other nanotubes. Therefore,
incorporating inorganic nanotubes (e.g. WS.sub.2) in metal-alloys
was not previously attempted.
[0102] In one embodiment, this invention demonstrates the
successful incorporation of inorganic nanotubes into metal alloys.
It is shown that WS.sub.2 nanotubes are highly beneficial for
improving the mechanical properties of the Mg alloys. For
comparison, carbon nanotubes were used but did not exhibit
satisfactory results when added to the metal alloys.
[0103] In one embodiment, metal alloy composites of this invention
are produced by stir casting. In one embodiment, stir-casting
methods of this invention are modified to be compatible with
small-volume molds. In one embodiment, molds used for the
preparation of the present composites is designed to comprise about
200 g of melt and is different from previously used molds
comprising about 2000 g of melt.
[0104] In one embodiment, the novel composites of this invention
comprise a combination of WS.sub.2 nanotubes and Mg alloy. In one
embodiment, the novel composites of this invention comprise very
small amounts (up to 1%) of nanotubes in a metal-alloy. Although
very small amount of nanotubes are incorporated in the alloys,
significant improvements in both the stiffness and ductility of the
alloy is demonstrated, leading to surprisingly high fracture
toughness of the metal matrix composites.
[0105] In one embodiment, the high temperature (>700.degree. C.)
melt stirring process leads to the significant improvements in
stiffness and ductility, and to the surprisingly high fracture
toughness of the composite.
[0106] Nanoparticles of inorganic layered compounds, like WS.sub.2,
MoS.sub.2 and numerous others, fold into tubular particles
(inorganic nanotube, INT) and into quasi-spherical inorganic
fullerene-like (IF) structures (spherical or quasi-spherical
nanoparticles). When added in small amounts to lubricating fluids,
these nanoparticles were shown to endow superior tribological
behavior to a variety of fluid lubricants.
[0107] The enhanced tribological properties of the IF nanoparticles
were attributed to their high strength and impact resistance as
well as to their ability to roll and their gradual exfoliation and
formation of a protective layer on the matting surfaces. Following
extensive studies, industrial grade IF-WS.sub.2 nanoparticles were
successfully commercialized, primarily for use as additives to
high-performance lubricants and greases ("NanoLub") and also in
surface protective polymer films.
[0108] In addition, the recent successful synthesis of pure
WS.sub.2 nanotubes (INT-WS.sub.2) powder paved the way for numerous
studies offering them numerous other applications. FIG. 1A shows a
scanning electron microscope (SEM) micrograph of an assortment of
WS.sub.2 nanotubes, while FIG. 1B displays a transmission electron
microscope (TEM) image of one such multiwall nanotube. The high
degree of crystalline perfectness of the nanotube can be
appreciated from these figures. This is also reflected by the
excellent mechanical properties of such nanotubes. Additionally,
the absence of major defects in the crystalline structure of the
nanotubes could promote their relative high-temperature stability
and impede their oxidation during a melt-stirring process of the
MMC.
[0109] The application of nanoparticles for improving the
tribological properties of polymer composites has been previously
demonstrated. However, the processing temperature of such
composites does not exceed 350.degree. C. Such temperature range
does not jeopardize the thermal stability of the nanoparticles.
[0110] Preparation of metallic composites involves appreciably
higher processing temperatures. Furthermore, molten metals are
known to be very reactive with respect to sulfur and its compounds
at high temperatures. This fact was expected to impair the
properties of metal-matrix composites comprising nano
structures.
[0111] In one embodiment, this invention provides the first bulk
metal composite reinforced with WS.sub.2 nanotubes. The
strengthening mechanisms of these composites are discussed. For
comparison, multiwall carbon nanotubes (CNT)-Mg-alloy MMC's were
also prepared in this series of experiments. Noticeably, they did
not produce any reinforcement effect in this case (see Table
1).
[0112] The novel INT-WS.sub.2-based Mg composites of this
invention, were prepared by melt-stirring with no further
mechanical or chemical processing. These novel INT-WS.sub.2-based
Mg composites revealed stronger and tougher properties compared
with the pure Mg alloy. This kind of behavior cannot be found in
traditional Mg alloys or in Mg composites reinforced by non-layered
nanoparticles. Usually, improving the tensile strength of a given
material by processing or by adding nanoparticles leads to
deterioration of the strain, and vice versa. Improving both strain
and strength by severe plastic deformation has been demonstrated.
However, such alloys suffered from stress corrosion and exhibited
low performance. Surprisingly, the present new Mg composites
exhibit both increased tensile strength and elongation (strain)
simultaneously. Thus, one of the main goals of this study is to
produce new Mg nano-MMCs with superior strength and strain. Such
new Mg nano-MMCs could be implemented in the 4C industry (Computer,
Communications, Consumer Electronics and Car) and could be used for
the aerospace industry and other industries as well.
Composites of the Invention
[0113] In one embodiment, this invention provides a metal-alloy
composite comprising: [0114] metal alloy; and [0115] inorganic
layered nanostructured material.
[0116] In one embodiment, this invention provides a metal composite
comprising: [0117] a metal; and [0118] inorganic layered
nanostructured material.
[0119] In one embodiment, the metal alloy comprises Mg, Fe, Cu, Al,
Ti, Zn, Ni, Hg, Mn, Ag, Au or a combination thereof. In one
embodiment, the base metal in said metal alloy is Fe, Cu, Al, Ti,
Zn, Ni, Hg. In one embodiment, the base metal in the metal alloy is
Mg.
[0120] In one embodiment, the metal alloy comprises one or more
secondary metals. In one embodiment, the secondary metal(s) in the
metal alloy is Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn or a combination
thereof. In one embodiment, the secondary metal(s) in the metal
alloy is Al, Zn, Mn or a combination thereof.
[0121] In one embodiment, the secondary metal(s) (or semi metals)
in said metal alloy is selected from the group consisting of Zn,
Al, Cu, Mg, Mn, Sn, Sb, Ag, Au, Pt, Pd, In, Zr, Ni Fe, C, Si, Ti,
Pb, Be, Y, Ce, Nd, Ca, Os, As, Ba, B, Cr, Co, Ga, Ge, Li, Rh, Ru,
Se, Sr, W, Na, Pt, Cd, Bi, or a combination thereof. In one
embodiment, the secondary metal is the alloying element of the
alloy.
[0122] In one embodiment, the metal alloy further comprises metal
impurities. In one embodiment, the metal impurities comprise one or
more metals at a wt % of not more than 0.001%, or of not more than
0.01%, or of not more than 0.1%, or of not more than 1% for each
metal impurity. In one embodiment, impurities at below 1% are added
to metal alloys of this invention to enhance a certain property,
such as chemical inertness or a mechanical property. In one
embodiment, the impurity materials are selected from metals,
metalloids, semi-metals, non-metals or a combination thereof. In
one embodiment, impurities such as Zn, Al, Cu, Mg, Mn, Sn, Sb, Ag,
Au, Pt, Pd, In, Zr, Ni Fe, C, Si, Ti, Pb, Be, Y, Ce, Nd, Ca, Os,
As, Ba, B, Cr, Co, Ga, Ge, Li, Rh, Ru, Se, Sr, W, Na, Pt, Cd, Bi,
Si or combinations thereof are added to metal alloys of this
invention. In one embodiment, the impurities comprise Si, Fe, Cu,
Mn, Zn, Al or a combination thereof.
[0123] In another embodiment, there is no distinction between
secondary metal and impurity. According to this aspect and in one
embodiment, all impurities in metal alloys of this invention are
regarded as secondary metals.
[0124] In another embodiment, impurities are materials that were
not intentionally added to the alloy or to the layered
nanostructure or to the composite, but nevertheless are found in
the metal alloy/composite in percentages smaller than 1% or smaller
than 0.1% or smaller than 0.01% or smaller than 0.001%. According
to this aspect and in one embodiment, such impurities do not affect
the properties of the metal alloy composite. Accordingly and in one
embodiment, metal alloys of this invention comprise impurities
which were unintentionally added. In one embodiment, the source of
such impurities is in the raw materials used, in materials used in
the process (e.g. gases), materials from the process environment,
materials from process components (e.g. crucible and hoses), or a
combination thereof.
[0125] In one embodiment, the inorganic layered nanostructured
material comprises a spherical or a quasi-spherical nanoparticle, a
nanotube, a nanoscroll, a sheet, a distorted sheet, a nano-platelet
or a combination thereof.
[0126] In one embodiment, the inorganic layered nanostructured
material does not comprise carbon. In one embodiment, the inorganic
layered nanostructured material does not comprise carbon nanotubes
or carbon fullerenes or carbon fullerene-like (nested-multiwall
polyhedral carbon) nanoparticles.
[0127] In other embodiments, the inorganic layered nanostructured
material comprises both carbon layered nanostructured material and
other non-carbon layered inorganic nanostructured material. In one
embodiment, the inorganic layered nanostructured material comprises
carbon nanotubes, carbon fullerenes, carbon fullerene-like
nanoparticles, graphene nano-platelets or a combination
thereof.
[0128] In one embodiment, the layered inorganic nanostructured
material comprises WS.sub.2, MoS.sub.2, or a combination
thereof.
[0129] In one embodiment, the sulfur-containing compound is
2H-phase WS.sub.2. In one embodiment, the layered inorganic
nanostructured material comprises any non-carbon, inorganic layered
nanomaterial.
[0130] In one embodiment, the concentration of the layered
inorganic nanostructured material in the composite ranges between
0.001 wt % to 15 wt %. In one embodiment, the concentration of the
layered inorganic nanostructured material in the composite ranges
between 0.001 wt % and 1 wt %.
[0131] In one embodiment, the concentration of the layered
inorganic nanostructured material in the composite ranges between
0.001% and 1%. In one embodiment, the concentration of the layered
inorganic nanostructured material in the composite ranges between
0.0001% and 1% or between 0.01% and 1% or between 0.1% and 1% or
between 0.001% and 5% or between 0.01% and 2% or between 0.001% and
10% or between 0.0001% and 15% or between 0.1% and 7.5% or between
0.1% and 20% or between 0.001% and 0.1% or between 0.0001% and
0.01% or between 0.0001% and 0.1%. In one embodiment, the
concentration of the layered inorganic nanostructured material in
the composite is less than 1%. In other embodiments, the
concentration of the layered inorganic nanostructured material in
the composite is less than 10%. In some embodiments, the
concentration is less than 5%. In some embodiments, the
concentration is less than 0.1%.
[0132] In one embodiment, there is an increase in fracture
toughness of the composite with respect to an alloy without the
inorganic layered nanostructure. In one embodiment, the % increase
in fracture toughness of the composite with respect to an alloy
without the inorganic layered structure ranges between 15% and 20%.
In one embodiment, the % increase in fracture toughness of the
composite with respect to an alloy without the inorganic layered
structure ranges between 20% and 50%. In some embodiments, the %
increase in fracture toughness ranges between 10% and 50%, between
10% and 100%, between 25% and 75%, between 50% and 150%, between 5%
and 100%, between 10% and 300%. In some embodiments, the % increase
in fracture toughness ranges between 10% and 200%, between 100% and
300%, between 250% and 300%, between 25% and 250%. In some
embodiments, the % increase in fracture toughness is up to 272%. In
some embodiments, the % increase in fracture toughness is up to
400%.
[0133] In one embodiment, there is an increase in yield strength of
the composite with respect to an alloy without the inorganic
layered structure. In one embodiment, the % increase in yield
strength of the composite with respect to an alloy without the
inorganic layered structure ranges between 15% and 20%. In one
embodiment, the % increase in yield strength of the composite with
respect to an alloy without the inorganic layered structure ranges
between 20% and 50%. In some embodiments, the % increase in yield
strength ranges between 10% and 50%, between 10% and 100%, between
25% and 75%, between 50% and 150%, between 5% and 100%, between 10%
and 75%. In some embodiments, the % increase in yield strength
ranges between 10% and 200%, between 100% and 200%, between 25% and
250%. In some embodiments, the % increase in yield strength is up
to 200%.
[0134] In one embodiment, there is an increase in ultimate tensile
strength of the composite with respect to an alloy without the
inorganic layered structure. In one embodiment, the % increase in
ultimate tensile strength of the composite with respect to an alloy
without the inorganic layered structure ranges between 45% and 70%.
In one embodiment, the % increase in ultimate tensile strength of
the composite with respect to an alloy without the inorganic
layered nanostructure ranges between 25% and 75%. In some
embodiments, the % increase in ultimate tensile strength ranges
between 10% and 100%, between 40% and 60%, between 10% and 150%,
between 50% and 150%, between 5% and 100%, between 10% and 75%. In
some embodiments, the % increase in ultimate tensile strength
ranges between 10% and 200%, between 100% and 200%, between 25% and
250%. In some embodiments, the % increase in ultimate tensile
strength is up to 200%.
[0135] In one embodiment, there is an increase in elongation of the
composite with respect to an alloy without the inorganic layered
nanostructure. In one embodiment, the % increase of elongation of
the composite with respect to an alloy without the inorganic
layered structure ranges between 140% and 400%. In one embodiment,
the % increase of elongation of the composite with respect to an
alloy without the inorganic layered structure ranges between 100%
and 500%. In some embodiments, the % increase of elongation ranges
between 200% and 600%, between 50% and 250%, between 100% and
1000%, between 50% and 750%, between 5% and 1000%, between 50% and
500%. In some embodiments, the % increase of elongation ranges
between 200% and 800%, between 50% and 800%, between 10% and 800%.
In some embodiments, the % increase of elongation is up to
800%.
[0136] In one embodiment, the grain size of metal-alloy composites
of this invention is smaller than the grain size of the
corresponding alloy without the inorganic layered structure. In one
embodiment, the size of the grains of the composite ranges between
50 .mu.m-100 .mu.m. In one embodiment, the size of the grains of
the composite ranges between 10 .mu.m-200 .mu.m. In some
embodiments, the grain size of metal-alloy composites of this
invention ranges between 1 .mu.m-100 .mu.m, between 0.5 .mu.m-250
.mu.m, between 25 .mu.m-75 .mu.m, between 10 .mu.m-100 .mu.m,
between 50 .mu.m-200 .mu.m, between 50 .mu.m and 500 .mu.m. In some
embodiments, the grain size of metal-alloy composites of this
invention ranges between 100 .mu.m-500 .mu.m, between 400 .mu.m-600
.mu.m, between 10 .mu.m-500 .mu.m, between 1-600 .mu.m.
Methods of Producing Composites of the Invention
[0137] In one embodiment, this invention provides a method for
producing a metal-alloy composite comprising: [0138] metal alloy;
and [0139] layered inorganic nanostructures; wherein the method
comprises: [0140] a. placing the metal alloy and the inorganic
layered nanostructured material in a crucible; [0141] b. heating
the metal alloy and the inorganic layered nanostructured material
in the crucible to a first temperature, thus forming a melt; [0142]
c. stifling the melt of the metal alloy and the inorganic layered
nanostructured material in the crucible; [0143] d. bringing gas
into contact with the melt in the crucible; [0144] e. optionally
heating the melt in the crucible to a second temperature; [0145] f.
optionally heating the melt in the crucible to a third temperature;
[0146] g. pouring the melt into a mold; [0147] h. cooling the melt,
thus forming a solid metal-alloy composite.
[0148] In one embodiment, this invention provides a method for
producing a metal composite comprising: [0149] a metal; and [0150]
layered inorganic nanostructures; wherein said method comprises:
[0151] a. placing said metal and said inorganic layered
nanostructured material in a crucible; [0152] b. heating said metal
and said inorganic layered nanostructured material in said crucible
to a first temperature, forming a melt; [0153] c. stirring said
melt of said metal and said inorganic layered nanostructured
material in said crucible; [0154] d. bringing gas into contact with
said melt in said crucible; [0155] e. optionally heating said melt
in said crucible to a second temperature; [0156] f. optionally
heating said melt in said crucible to a third temperature; [0157]
g. pouring said melt into a mold; [0158] h. cooling said melt, thus
forming a solid metal composite.
[0159] In one embodiment, the order of steps b, c, d or any
combination thereof is switched or reversed. In one embodiment,
steps b, c, d or any combination thereof are conducted in parallel
or at least partially overlap in time.
[0160] In one embodiment, the first temperature is 380-420.degree.
C., said second temperature is 580-620.degree. C. and said third
temperature is 680-720.degree. C.
[0161] In one embodiment, the first temperature ranges between
200-700.degree. C. In one embodiment, the first temperature ranges
between 500-700.degree. C. In one embodiment, the first temperature
ranges between 600-700.degree. C., between 700-800.degree. C.,
between 700-900.degree. C., between 750-850.degree. C., between
700-1000.degree. C., between 1000-1300.degree. C., between
1200-1500.degree. C. In one embodiment, the first temperature is up
to 1000.degree. C. In one embodiment, the first temperature is up
to 1300.degree. C. In one embodiment, the first temperature is up
to 1500.degree. C. In one embodiment, the first temperature ranges
between 300-500.degree. C. or between 300-700.degree. C. In some
embodiments, the first temperature is 400.+-.25.degree. C.,
450.+-.25.degree. C., 500.+-.25.degree. C., 550.+-.25.degree. C.,
600.+-.25.degree. C., 650.+-.25.degree. C., 700.+-.25.degree. C.,
700-730.degree. C., 750.+-.25.degree. C., 800.+-.25.degree. C.,
850.+-.25.degree. C., 900.+-.25.degree. C., 950.+-.25.degree. C.,
1000.+-.25.degree. C., 1050.+-.25.degree. C., 1100.+-.25.degree.
C., 1150.+-.25.degree. C., 1200.+-.25.degree. C.,
1250.+-.25.degree. C., 1300.+-.25.degree. C. 1350.+-.25.degree. C.,
1400.+-.25.degree. C., 1450.+-.25.degree. C., 1500.+-.25.degree.
C.
[0162] In one embodiment, heating to the first temperature is
conducted during a period of a few minutes. In one embodiment,
heating to the first temperature is conducted during a period
ranging between 10 minutes and 60 min.
[0163] In one embodiment, heating to the first temperature is
conducted during a period of a few hours. In one embodiment,
heating to the first temperature is conducted during a period of
1-3 hours. In one embodiment, heating to the first temperature is
conducted during a period of 20 min to 3 hours, or 10 min to 3
hours, or 1-4 hours, or 1-5 hours, or 0.5-2 hours, or 0.5-4 hours.
Heating to the first temperature is the time it takes to heat until
reaching the first temperature.
[0164] In some embodiments, the crucible, and/or the materials in
the crucible (or in any other vessel) are kept at the first
temperature for a period of time of 10 min-1 hr. In some
embodiments, the crucible, and/or the materials in the crucible (or
in any other vessel) are kept at the first temperature for a period
of time of 1 min-5 hr. In some embodiments, the crucible, and/or
the materials in the crucible (or in any other vessel used) are
kept at the first temperature for a period of time of 5 min-50 min,
or for 10 min-2 hr, or for 0.5 hr-2.5 hr, or for 1 min-10 min, or
for 10 min-10 hr, or for 1 hr-3 hr.
[0165] In one embodiment, the time required to heat the sample from
the first temperature to the second temperature and/or from the
second temperature to the third temperature is at the same ranges
described herein above for the time required to heat the sample to
the first temperature.
[0166] In one embodiment, the time the sample is kept at the second
temperature and/or at the third temperature is within the same
ranges described herein above for the time the sample is kept at
the first temperature.
[0167] Any other time ranges and temperature ranges are applicable
to methods and systems of this invention, depending on parameters
of the system, of the materials used, the mass/volume of the alloy
used, the power of the furnace etc. as is known to any person of
ordinary skill in the art.
[0168] In one embodiment, where the method further comprises
heating to a second and optionally to a third temperature (optional
steps e and f), the second temperature is higher than the first
temperature and the third temperature is higher than the second
temperature. In one embodiment, where the method further comprises
heating to a second and optionally to a third temperature, the
second and third temperatures are at any suitable range. In one
embodiment, the first temperature ranges between 300 and
500.degree. C., the second temperature ranges between 500 and
700.degree. C. and the third temperature ranges between 600 and
800.degree. C.
[0169] In one embodiment, the second temperature and the third
temperatures range between 300 and 1000.degree. C.
[0170] In one embodiment, gas is brought into contact with the melt
in the crucible. In embodiments wherein the gas is introduced to
the system before the heating step is performed, the gas is brought
into contact with the solids in the crucible.
[0171] The gas introduced into the system is the gas that is
brought into contact with the melt or with the mixture of solids in
the crucible as shown in FIG. 2A. In one embodiment, the gas
introduced in to the system is selected from the group consisting
of CO.sub.2, SF.sub.6, N.sub.2, Ar or a combination thereof. In one
embodiment, any gas or any gas mixture that does not interfere
with, or deteriorate or prevents the formation of the novel metal
alloy composites of this invention can be used in embodiments of
this invention.
[0172] In one embodiment, the melt is kept at the first temperature
and optionally at the second temperature and optionally at the
third temperature for a period of time ranging between 10 min-20
min. In one embodiment, the melt is kept at the first temperature
and optionally at the second temperature and optionally at the
third temperature for a period of time ranging between 1 min-50
min. In one embodiment, the melt is kept at the first temperature
and optionally at the second temperature and optionally at the
third temperature for a period of time ranging between 5 min-25
min, or between 1 min-100 min, or between 0.5 min-30 min, or
between 12.5 min-17.5 min, or between 10 min-200 min, or between
0.1 min-50 min.
[0173] In one embodiment, heating is conducted in a
resistance-heating furnace. In one embodiment, heating is conducted
in any furnace or oven or vessel that can reach the temperature(s)
needed for methods of this invention. In one embodiment, heating
comprises solar heating.
[0174] In one embodiment, the stirring is conducted using a
stirrer. In one embodiment, the stirrer comprising a vane, a blade,
a rod, a screw or a combination thereof. In another embodiment, no
stirring is conducted in methods of this invention.
[0175] In other embodiments, gas stirring is used. Gas stirring is
conducted using N.sub.2 or Ar in some embodiments. In some
embodiments, a combination of stirring methods is used.
[0176] In one embodiment, instead of a crucible, any other suitable
vessel may be used. An ampoule, a solid substrate, a powdered
substrate, a mold, a vessel, a cylinder, or any other device can be
used. The crucible or any other appropriate vessel may be made from
any material that can hold the metal alloy and the inorganic
layered structures and that can sustain the temperatures applied in
methods of this invention. In one embodiment, the crucible or any
other vessel or device is inert to the metal-alloy and the
inorganic layered structures at the temperatures used in methods of
this invention.
[0177] In one embodiment, this invention provides a method for
producing a metal-alloy composite comprising: [0178] metal alloy;
and [0179] layered inorganic nanostructures; wherein said method
comprises: [0180] heating a metal alloy to form a metal solution;
[0181] adding a layered inorganic nanostructure into the metal
solution; [0182] cooling down the metal solution containing the
metal alloy and the layered inorganic nanostructures to form a
composite material; and [0183] optionally performing a solid
solution treatment to the composite material.
[0184] In one embodiment, this invention provides a method for
producing a metal composite comprising: [0185] a metal; and [0186]
layered inorganic nanostructures; wherein said method comprises:
[0187] heating a metal to form a melt; [0188] adding a layered
inorganic nanostructure into the metal melt; [0189] cooling down
the metal melt containing the metal and the layered inorganic
nanostructures to form a composite material; and [0190] optionally
performing a solid solution treatment to the composite
material.
[0191] In one embodiment, the metal alloy is a magnesium-based
alloy or an aluminum-based alloy. In one embodiment, the layered
inorganic nanostructure is a sulfur-containing compound. In one
embodiment, the sulfur-containing compound comprises tungsten
disulfide (WS.sub.2), molybdenum disulfide (MoS.sub.2) or a
combination thereof. In one embodiment, the method further
comprises introducing a protective gas when heating the metal or
the metal alloy.
[0192] In one embodiment, introduction of the protective gas
comprises introducing helium (He), argon (Ar), nitrogen (N.sub.2),
sulfur hexafluoride (SF.sub.6), carbon dioxide (CO.sub.2) or a
combination thereof. In one embodiment, the protective gas
introduction is stopped after holding a temperature of between
600.degree. C. and 800.degree. C. for 1 min to 2 hour.
[0193] In one embodiment, this invention provides a metal or a
metal-alloy composite comprising: [0194] metal or metal alloy; and
[0195] inorganic layered nanostructured material; [0196] wherein
the metal composite or the metal-alloy composite is produced by any
of the methods described herein above.
[0197] As will be further described in the examples herein below,
small amounts of up to 1 wt % of WS.sub.2 nanotubes (INT-WS.sub.2)
were added to the AZ31 Mg-alloy using a melt-stirring reactor
operated at 700-730.degree. C. Notwithstanding partial oxidation,
the nanotubes showed quite a remarkable stability at these elevated
processing temperature and were distributed quite uniformly in the
processed ingot. Despite the small amounts of added INT-WS.sub.2,
their addition led to remarkable improvements in the mechanical
properties of the alloys. Surprisingly, both the tensile strength
of the AZ31 alloy and its elongation (and consequently the fracture
toughness) were greatly improved.
[0198] Metallographic analysis of the alloys clearly showed that
the thermal mismatch between the nanotubes and the Mg-alloy leads
to the formation of numerous dislocations in the grain boundaries
in the vicinity of the nanotube-matrix interface. These
dislocations impede the progress of the crack under load.
[0199] Contrarily, carbon nanotubes which were added to the same
alloy using the melt-stirring technique (see Table 1), did not show
any favorable effect on the mechanical properties of such
alloys.
TABLE-US-00001 TABLE 1 Summary of mechanical measurements of
Mg-MMC's, mechanical properties of present nanocomposites and other
nanocomposites. Ultimate tensile Yield strength, strength [MPa]
[MPa] Elongation Notation Specification (% change) (% change) (%
change) AZ31 .sup.a) As-cast AZ31 Mg 84.3 (0) 136.0 (0) 5.3% (0)
alloy AZ31INT0.5 .sup.a) AZ31 with 0.5 wt. % 101.1 (+20.0) 203.0
(+49.3) 12.7% (+139.6) WS.sub.2 nanotubes AZ31INT1 .sup.a) AZ31
with 1 wt. % 99.0 (+17.4) 227.7 (+67.4) 25.1% (+373.6) WS.sub.2
nanotubes AZ31CNT0.1 .sup.e) AZ31 with 0.1 wt. % 62.5 (-25.6) 104.8
(-22.9) 3.25% (-38.7) CNT AZ31CNT0.5 .sup.e) AZ31 with 0.5 wt. %
64.0 (-24.1) 114.4 (-15.9) 4.73% (-10.8) CNT Pure Mg .sup.b) Pure
Mg 47 .+-. 3 (0) 120 .+-. 4 (0) 12.3 .+-. 1.1% (0) Mg-1 wt % SiC
.sup.b) Pure Mg with 1 wt. % 67 .+-. 4 (+42.0) 133 .+-. 5 (+10.8)
6.3 .+-. 0.8% (-48.8) SiC nanoparticles AZ91 .sup.c) As-cast AZ91
Mg 250 (0%) 350 (0%) 16.5% (0%) alloy AZ91MWCNT0.1 .sup.c) AZ91
with 0.1 wt. % 300 (+20.0) 415 (+18.6) 24.5% (+48.5) CNT AZ91
.sup.d) As-cast AZ91 Mg alloy 135 (0) 210 (0) 6% (0) AZ91MWCNT0.1
.sup.d) AZ91 with 0.7 wt. % 210 (+55) 305 (+45) 9% (+50) CNT + 0.3
wt. % SiC .sup.a) Present work: AZ31 and WS.sub.2 nanotubes-AZ31
nanocomposite; .sup.b) literature .sup.c) literature; .sup.d)
literature; .sup.e) Present work: CNT AZ31 nanocomposite; ( )
Brackets indicate % change with respect to the corresponding
monolithic alloy.
Theory:
[0200] Several mechanisms have been offered to explain the
reinforcement effect of nanoparticles in different crystalline
matrices. Primarily, the Hall-Petch mechanism, which relates the
grain size to the fracture toughness of the matrix could be
anticipated. More careful analysis for the contribution of each of
the four reinforcement mechanisms discussed above was carried-out.
Unfortunately, only nanoparticles with isotropic spherical shape
could be used in for these calculations. A representative example
for such calculations with the different models and parameters used
are presented in Table 2.
TABLE-US-00002 TABLE 2 Calculated contributions of the different
mechanisms for the reinforcement of the AZ31 by 0.1 wt %
INT-WS.sub.2, assuming the diameter of the nanoparticles is 100 nm.
Percentage of Value strengthening Symbol Description [MPa]
contribution .DELTA..sigma..sub.Hall-Petch enhancement of composite
6.4698 14.4% strength due to grain refining .DELTA..sigma..sub.CTE
enhancement of composite 31.2113 69.7% strength due to dislocation
density increase .DELTA..sigma..sub.Orowan enhancement of composite
7.0407 15.7% strength due to Orowan strengthening
.DELTA..sigma..sub.load enhancement of composite 0.09834 0.2%
strength due to load bearing
[0201] It is clear from the calculations that the greatest
contribution for the reinforcement effect is the increase in the
dislocations density at the nanotube-Mg-alloy matrix due to the
large mismatch in the thermal expansion of the two materials. In
contrast to the Hall-Petch mechanism this effect is more local and
is limited to the grain boundaries in the vicinity of the
nanotube-metal interface. These calculations were not particularly
sensitive to the size of the nanoparticles (e.g. 20-100 nm).
However, models taking into account the large anisotropy of the
nanotubes would be highly warranted in this case. Further research
is required to optimize the process and elucidate the mechanism of
the reinforcement effect--in particular using advanced electron
microscopy techniques.
[0202] Analysis of the contribution of each of the four models to
the improved mechanical properties of the Mg-MMC's with different
concentration of WS.sub.2 nanotubes is detailed herein below:
[0203] Model 1: Hall-Petch Strengthening
.DELTA..sigma..sub.Hall-Petch=K.sub.y(d.sub.m.sup.-1/2-d.sub.c.sup.-1/2)
[0204] Model 2: Coefficient of Thermal Expansion Difference
Effect
.DELTA..sigma. CTE = 3 .beta. G m b 12 V p ( .alpha. m - .alpha. p
) ( T process - T test ) ( 1 - V P ) bd p ##EQU00001##
[0205] Model 3: Orowan Strengthening
.DELTA..sigma. Orowan = 0.13 G m b d p [ ( 1 2 V p ) 1 / 3 - 1 ] ln
d p 2 b ##EQU00002##
[0206] Model 4: Load Bearing Effect
.DELTA..sigma..sub.load=0.5V.sub.p.sigma..sub.ym
[0207] 1. AZ31-0.1 wt % (WS.sub.2)
TABLE-US-00003 TABLE 3 Parameter for calculation Parameter
Description Value Reference/note .alpha..sub.m coefficient of
thermal expansion of 27.9 .times. 10.sup.-6.degree. C..sup.-1 Mg
alloys-design, the matrix processing and properties F. Czerwinski
2011 .alpha..sub.p coefficient of thermal expansion of 15.96
.times. 10.sup.-6.degree. C..sup.-1 RSC Adv. 2015, 5, the
nanoparticles 18391-18400 .beta. dislocation strengthening
coefficient 1.25 Acta Materialia 2007, 55, 5115-5121 b magnitude of
the burgers vector 0.32 nm Mat. Sci. Eng. A 2008, 483-484, 148-152
d.sub.c average grain size in the composite 82.7 .mu.m
experimentally sample determined d.sub.m average grain size in the
monolithic 227.9 .mu.m experimentally sample determined d.sub.p
nanoparticle diameter 100 nm manufacture supplied average particle
size G.sub.m shear modulus of the matrix 16.7 GPa calculation and
experimentally determined k.sub.y Hall-Petch material constant
0.0145 MPa{square root over (m)} calculation and experimentally
determined T.sub.process processing temperature 720.degree. C. --
T.sub.test testing temperature 25.degree. C. -- V.sub.p volume
fraction of nanoparticles 0.000023 calculated from weight fraction
.sigma..sub.ym Yield stress of the matrix 84.3 MPa experimentally
determined
TABLE-US-00004 TABLE 4 Calculated contributions of the different
mechanisms for the reinforcement of the AZ31 by 0.1 wt %
INT-WS.sub.2. Percentage of Value strengthening Symbol Description
[MPa] contribution .DELTA..sigma..sub.Hall-Petch enhancement of
composite 0.6634 13.1% strength due to grain refining
.DELTA..sigma..sub.CTE enhancement of composite 3.0954 61.1%
strength due to dislocation density increase
.DELTA..sigma..sub.Orowan enhancement of composite 1.3041 25.8%
strength due to Orowan strengthening .DELTA..sigma..sub.load
enhancement of composite 0.0001 0.0% strength due to load
bearing
[0208] 2. AZ31-0.5 wt % (WS.sub.2)
TABLE-US-00005 TABLE 5 Parameter for calculation Parameter
Description Value Reference/note d.sub.c average grain size in the
136.9 .mu.m experimentally composite sample determined d.sub.m
average grain size in the 227.9 .mu.m experimentally monolithic
sample determined d.sub.p nanoparticle diameter 100 nm manufacture
supplied average particle size V.sub.p volume fraction of 0.001162
calculated from weight nanoparticles fraction
TABLE-US-00006 TABLE 6 Calculated contributions of the different
mechanisms for the reinforcement of the AZ31 by 0.5 wt %
INT-WS.sub.2. Percentage of Value strengthening Symbol Description
[MPa] contribution .DELTA..sigma..sub.Hall-Petch enhancement of
composite 5.1333 15.8% strength due to grain refining
.DELTA..sigma..sub.CTE enhancement of composite 22.0142 67.6%
strength due to dislocation density increase
.DELTA..sigma..sub.Orowan enhancement of composite 5.3581 16.4%
strength due to Orowan strengthening .DELTA..sigma..sub.load
enhancement of composite 0.0490 0.2% strength due to load
bearing
[0209] 3. AZ31-1 wt % (WS.sub.2)
TABLE-US-00007 TABLE 7 Parameter for calculation Parameter
Description Value Reference/note d.sub.c average grain size in 77.2
.mu.m experimentally the composite sample determined d.sub.m
average grain size in 227.9 .mu.m experimentally the monolithic
sample determined d.sub.p nanoparticle diameter 100 nm manufacture
supplied average particle size V.sub.p volume fraction of 0.002333
calculated from weight nanoparticles fraction .sigma..sub.ym Yield
stress of the 84.3 MPa experimentally matrix determined
TABLE-US-00008 TABLE 8 Calculated contributions of the different
mechanisms for the reinforcement of the AZ31 by 1 wt %
INT-WS.sub.2. Percentage of Value strengthening Symbol Description
[MPa] contribution .DELTA..sigma..sub.Hall-Petch enhancement of
composite 6.4698 14.4% strength due to grain refining
.DELTA..sigma..sub.CTE enhancement of composite 31.2113 69.7%
strength due to dislocation density increase
.DELTA..sigma..sub.Orowan enhancement of composite 7.0407 15.7%
strength due to Orowan strengthening .DELTA..sigma..sub.load
enhancement of composite 0.09834 0.2% strength due to load
bearing
[0210] In one embodiment, this invention provides a method for
producing a metal-alloy composite comprising: [0211] metal alloy;
and [0212] layered inorganic nanostructures; wherein said method
comprises: [0213] heating a metal alloy to form a metal solution;
[0214] adding a layered inorganic nanostructure into the metal
solution; [0215] cooling down the metal solution containing the
metal alloy and the layered inorganic nanostructures to form a
composite material; and [0216] optionally performing a solid
solution treatment to the composite material.
[0217] FIG. 8 illustrates embodiments of this method. FIG. 8 is a
flow chart of a method 800 for making a metal alloy composite
material, the method comprises gravity casting. Additional
operations may be provided before, during, and after the steps
shown in the figure for this method, and some of the operations
shown for the method can be eliminated or replaced for additional
embodiments of the method. The material of the metal alloy
composite and the method for making the same are described in the
following with reference to FIG. 9.
[0218] The method 800 includes the following steps: a metal alloy
matrix is placed in a container (step 801); the metal alloy matrix
is heated up to a first temperature and a protective gas is
introduced into the container (step 804); the metal alloy matrix is
heated up to a second temperature (step 806); the metal alloy
matrix is heated up to a third temperature and introducing the
protective gas into the container is stopped (step 808); a
reinforcement is added into the container and is stirred with the
metal alloy matrix to form a mixing slurry (step 810); the mixing
slurry is cooled down to form a composite material (step 812); and
a solid solution treatment to the composite material is performed
(step 814). The detail information related to each of these steps
will be described later.
[0219] Gravity casting is commonly used as a general casting
process in manufacturing and is applicable to methods of this
invention as disclosed herein. However, in methods of this
invention, other casting methods can be used as known in the art.
For example, die casting, vacuum casting etc. can be used.
[0220] In some embodiments, the three-step heating process is
advantageous as the holding time in each temperature assists in the
process. According to this aspect and in one embodiment, heating to
only one temperature instead of a three-step heating to three
different temperature ranges is not preferred because of the lack
of holding time.
[0221] In other embodiments however, continuous heating may be used
instead of a three-step heating process. However, such heating
process consumes more energy and may cost more due to the expensive
protection gas used. Other modifications of the heating process are
possible in embodiments of this invention, including but not
limited to less or more heating steps, modified heating rates,
other selected temperatures at each step, and various holding times
at each temperature. Any other modifications of the heating process
are possible with embodiments of this invention as known in the
art.
[0222] In some embodiments, the protective gases used are as
follows: the first protective gas is Ar (cheaper, exhibiting
general protection only at lower temp. say less than 400.degree.
C.). The second protective gas is a mixture of SF.sub.6+CO.sub.2
(more expensive, exhibiting much effective protection for Mg at any
temperature). However, other gases, mixtures thereof and
combinations thereof can be used in methods of this invention as
protective gases.
[0223] In one embodiment, the protective gas is removed prior to,
during or immediately after introduction of the reinforcement
material. In other embodiments, the protective gas is kept during
or following the introduction of the reinforcement material.
However, reinforcement materials might be blown away by the
protective gas and/or may react with the SF.sub.6/CO.sub.2 gas
mixture in one embodiment.
[0224] An embodiment of a furnace as used in the method 800 for
making the metal alloy composite is shown in FIG. 9, wherein the
container mainly includes a resistance-type furnace 4, an external
first gas tank 5, an external second gas tank 8, and a mold 9 under
the resistance type furnace 4. Other elements such as a stirring
unit 6 and a heating unit 41 will be described herein below.
[0225] The method 800 starts from step 801 by placing a metal alloy
matrix 1 in a container 3. The container 3 is made of high
temperature material, for example, 310S stainless steel or high
temperature ceramics, or any suitable material. In the embodiment,
the container 3 is a 310S stainless steel crucible. The metal alloy
matrix 1 can be any pure metal, metal alloy, or metal/nonmetal
composite material. The metal alloy matrix 1 may include a metal
(i.e. Mg, Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn, Ag, and Au) and/or a
nonmetal (i.e. C, Si) or other suitable materials/compounds. In
some embodiments, the metal alloy matrix 1, or called Mg-based
alloy, is a metal alloy mainly composed of Mg, such as Mg alloy or
Mg--Al alloy (i.e. AZ series like AZ31, AZ61, and AZ80). In other
embodiments, the metal alloy matrix 1, or called Al-based alloy, is
a metal alloy mainly composed of Al, such as Al alloy or Al--Mg
alloy. In an embodiment, the metal alloy matrix 1 is a Mg-based
metal alloy including AZ31 and AZ61 Mg alloy. Therefore, the metal
alloy composite material formed by the method of the present
invention from the Mg-based alloy is Mg-based composite material.
In other embodiments, the metal alloy composite material formed by
the method of the present invention from the Al-based alloy is
Al-based composite material. Reference is now made to Table 9 and
Table 10 below. Table 9 shows the compositions of the AZ31 Mg alloy
and Table 2 shows the compositions of the AZ61 Mg alloy.
TABLE-US-00009 TABLE 9 the compositions of the AZ31 Mg alloy.
Element Al Mn Zn Fe Si Cu Ni Mg Weight 3.08 0.393 0.908 0.001 0.022
0.0017 0.0006 balanced Percentage (%)
TABLE-US-00010 TABLE 10 the compositions of the AZ61 Mg alloy.
Element Al Mn Zn Fe Si Cu Ni Mg Weight 6.5 0.15 0.85 0.07 0.3 0.07
0.009 balanced Percentage (%)
[0226] As shown in Table 9 and in Table 10, Mg is the major element
in AZ31 Mg alloy and in AZ61 Mg alloy and other elements such as
Al, Mn, Zn, Fe, Si, Cu, Ni, are doped into the AZ31 Mg alloy and
into the AZ61 Mg alloy. The content of Mg is balanced according to
other doping elements.
[0227] The method 800 proceeds to step 804 by heating the metal
alloy matrix up to a first temperature and introducing a protective
gas. In this step, the container 3 is first placed in the
resistance-type furnace 4 and the container 3 and the metal alloy
matrix 1 in the container 3 are heated by a heating unit 41. At
this time, the metal alloy matrix 1 melts with increasing
temperature. The first temperature is between 350.degree. C. and
500.degree. C. In the embodiment shown, the first temperature is
400.degree. C. Furthermore, in the progress of heating the metal
alloy matrix to the first temperature, the first protective gas is
introduced through the first gas vessel (or gas tube) 51 from the
external first gas tank 5 when the temperature is raised to a
degree between 250.degree. C. and 300.degree. C. to prevent the
metal alloy matrix 1 from contacting with air and prevention of the
oxidation reaction there between from occurring. The first
protective gas may include Ar, Ne, N.sub.2, fluoride, CO.sub.2, a
combination thereof, or other suitable gases. In an embodiment, the
first protective gas is Ar. Furthermore, the temperature at which
the first protective gas is introduced can be adjusted according to
the material of the metal alloy matrix 1. In another embodiment,
the protective gas is introduced at a temperature between room
temperature and the first temperature.
[0228] When the temperature is raised to the first temperature, the
second protective gas is introduced through the second gas vessel
(or gas tube) 81 from the external second gas tank 8 to prevent the
metal alloy matrix 1 from contacting air and preventing the
combustion reaction there between from occurring. Meanwhile, the
introduction of the first protective gas is stopped. The second
protective gas may include Ar, Ne, N.sub.2, fluoride, CO.sub.2, a
combination thereof, or other suitable gases. In the embodiment,
the second protective gas is a gas mixture of CO.sub.2 and
SF.sub.6. Moreover, the next step is performed after the
temperature is held for 1 min to 2 hours when the first temperature
is reached. In a specific embodiment, the holding time under the
first temperature is between 10 mins and 15 mins.
[0229] The aforementioned first protective gas and the second
protective gas can be chosen according to real requirements and the
material of the metal alloy matrix 1. In an embodiment, since the
metal alloy matrix 1 is Mg alloy or Mg--Al alloy, the protective
gas can be a gas mixture of CO.sub.2 and fluoride. Although Mg
alloy under CO.sub.2 atmosphere and at various temperatures has a
very low oxidation rate, Mg alloy or Mg--Al alloy may still have
combustion reaction with increasing temperature. Moreover, when
CO.sub.2 includes a mixture of air and moisture, the protective
ability of CO.sub.2 decreases. Therefore, the protective gas in
such embodiment, besides CO.sub.2, further includes fluoride.
[0230] In various fluoride gases, the SF.sub.6 is increasingly used
in melting Mg alloy to prevent the combustion of Mg alloy liquid.
In room temperature, SF.sub.6 is highly stable. At high
temperature, after SF.sub.6 undergoes a chemical reaction with Mg
alloy or Mg--Al alloy, a protective layer is formed on the surface
of the Mg alloy or Mg--Al alloy. Therefore, SF.sub.6 has an ability
of preventing the combustion reaction of Mg alloy liquid from
occurring. So, introducing protective gas can prevent the metal
alloy matrix 1 from contacting air and the combustion from
occurring during heating the metal alloy matrix 1. Moreover,
introducing the first or the second protective gas can provide a
stirring function by means of gas vibration.
[0231] The method 800 proceeds to step 806 by heating the metal
alloy matrix up to a second temperature. In this step, the
temperature raised from the first temperature to the second
temperature allows the metal alloy matrix 1 melting into a metal
solution more homogeneously. The second temperature is between
450.degree. C. and 700.degree. C. In the embodiment, the second
temperature is 600.degree. C. As mentioned before, the next step is
performed after the temperature is held for 1 min to 2 hours when
the second temperature is reached. In a specific embodiment, the
holding time under the second temperature is between 10 mins and 15
mins.
[0232] The method 800 proceeds to step 808 by heating the metal
alloy matrix up to a third temperature and stopping introducing the
protective gas. In this step, temperature is increased from the
second temperature to the third temperature in order to form a
metal solution 2 with higher homogeneity. The third temperature is
between 600.degree. C. and 800.degree. C. In an embodiment, the
third temperature is 730.degree. C. As mentioned before, the
temperature is held at the third temperature for 1 min to 2 hour
before proceeding to the next step. In the specific embodiment, the
temperature is held at the third temperature for 10 min to 15 min.
Then, introducing the first protective gas and the second
protective gas into the container is stopped, for the subsequent
step of adding the reinforcement into the container. That is to
say, in the embodiment, after holding temperature at the third
temperature (730.degree. C.) for 10 min to 15 min and stopping
introducing the first protective gas and the second protective gas,
the next step of adding the reinforcement into the metal solution 2
is then performed, which will be discussed later. In another
embodiment, the first protective atmosphere and/or the second
protective atmosphere is still introduced into the container after
increasing temperature to the third temperature.
[0233] The method 800 proceeds to step 810 by adding the
reinforcement (not shown) into the container 3 and stirring them to
form a mixing slurry (not shown). After holding the temperature for
10 mins to 15 mins and stopping introducing the second protective
gas when the third temperature (730.degree. C.) is reached, the
sealing cap 31 of the container 3 is opened for adding the
reinforcement. The reinforcement can be chosen and adjusted
properly according to real requirements and the material of the
metal alloy matrix 1. In an embodiment, the reinforcement is
sulfur-containing compound such as WS.sub.2, MoS.sub.2, or a
combination thereof. Furthermore, the shape of the reinforcement
may include but not limited to tubular, sheet, bulk, ball, or a
combination thereof. The adding content of the reinforcement is
between 0.001 wt % and 15 wt %. In the embodiment, the
reinforcement used was nano-tubular WS.sub.2, and the adding
content thereof was between 0.1 wt % and 0.2 wt %. These materials
have been used in embodiments of the processes of this invention.
The WS.sub.2 were synthesized according to previously described
procedures. However, the present disclosure is not limited the
aforementioned descriptions, for example, the material, shape, and
the adding content of the reinforcement added into the metal alloy
matrix 1 can be adjusted according to real requirements. It should
be noted that, in this embodiment, the WS.sub.2 reinforcement will
form a strengthen phase, i.e. 2H-phase (2H WS.sub.2 nanotubes)
having different phase structure from the metal alloy matrix in the
following heat treatment which will be discussed herein below. In
another embodiment, the WS.sub.2 reinforcement will form a
strengthen phase, i.e. 1T-phase, after the heat treatment.
Furthermore, the timing at which the reinforcement is added is
after the metal alloy matrix 1 melts into the metal solution 2, the
temperature is held at 730.degree. C. for 10 mins to 15 mins, and
the second protective gas is stopped being introduced. Therefore,
the reinforcement can distribute more homogeneously in the metal
solution 2 so that the mechanical properties of the metal alloy
composite material are better.
[0234] After adding the reinforcement into the metal solution 2, a
stirring unit 6 is used to stir the metal solution 2 to
homogeneously mix the metal solution and the reinforcement to form
homogeneous mixed slurry. The stirring unit 6 may include a motor
61 and stirring blades 62. To be more precise, in the embodiment,
the motor 61 is disposed over the sealing cap 31 of the container
3. There are two variable-speed motors 61 over the sealing cap 31.
The motor 61 may include but not limited to continuous
variable-speed motor. The stirring blades 62 can be disposed with a
tilted angle of 45.degree. towards different directions, and each
stirring rod has two sets of stirring blades 62 disposed in the
metal solution 2. When the stirring blade 62 stirs the metal
solution 2, it also stirs the reinforcement having higher density
and deposited at the bottom of the container 3. Therefore, the
reinforcement and the metal solution 2 can be homogeneously mixed
into the mixing slurry through the stirring unit 6. In general, the
motor 61 stirs at a stirring rate between about 300 RPM and about
470 RPM and for about 1 min to about 5 mins. In the embodiment, the
motor stirs at a stirring rate of about 300 RPM and for about 1
min. Furthermore, in another embodiment, the first protective gas
and/or the second protective gas is/are still introduced when
stirring the metal solution 2 and the reinforcement. Other stirring
systems and devices may be used in embodiments of this invention as
known in the art.
[0235] The method 800 proceeds to step 812 by pouring the mixing
slurry into the mold 9 and leave it to be cooled to form a
composite material (not shown). Since the mold 9 is isolated from
and under the container 3, the mold 9 can be pre-heated by the
heating unit 42 before pouring the mixing slurry into the mold 9
for decreasing the temperature difference between the mold 9 and
the mixing slurry to avoid drawbacks such as inhomogeneity caused
by the rapid cooling rate. Furthermore, the first protective gas
and/or the second protective gas may be introduced through the
first gas vessel 52 and/or the second gas vessel 82 before pouring
the mixing slurry into the mold 9 to prevent the contact and
reaction between air and the mixing slurry. After the stirring is
finished, the plug is pull up to open the nozzle 7 at the bottom of
the container 3, and the first protective gas and/or the second
protective gas are/is introduced through the first gas vessel 52
and the second gas vessel 82 to isolate the mixing slurry from air.
At the same time, the mixing slurry flows down into the mold 9
along the nozzle 7, cools and forms the composite material, or so
called ingot.
[0236] The method 800 proceeds to step 814 by performing a T4 solid
solution treatment to the composite material. The T4 represents
that solid solution treatment and the natural aging process were
performed to a stable state. The solid solution treatment is aimed
to make the sample more homogeneous and reduce stress. Ingot cooled
down from high temperature in casting process and solid solution
process generates residual stress. The residual stress is
eliminated by heating the ingot to a temperature at which the yield
stress is lower than the residual stress. The composite material in
the present disclosure has more defects in the bottom and the top
shrink head, and the grain structure in the middle portion is
better. Therefore, the specimens used for the following property
tests such as stretching test, metallographic analysis, hardness
test, and X-ray analysis, are taken from the middle portion of the
ingot.
[0237] In the embodiment, a heat treatment furnace (not shown) is
used to perform a solid solution (heat) treatment to the composite
material. The heat treatment is usually performed by raising
temperature with a fixed heating gradient to a pre-determined
temperature, and followed by keeping the temperature for a while,
then raising the temperature and holding the temperature for a
longer time again. The heating condition is according to the design
of the furnace. For example, the heating gradient can be 5.degree.
C./min, from the initial temperature to a temperature between
260.degree. C. and 270.degree. C. and the temperature is held for
an hour to release the residual stress in the composite material.
Then, the temperature is slowly increased at a heating gradient of
1.degree. C./min and takes 2 hours and 20 minutes to reach a
temperature of 400.degree. C. to 450.degree. C. and lasting for 10
hours. Then, the composite material is quenched by e.g. water. In
some embodiments, the temperature of the solid solution treatment
ranges from about 400.degree. C. to about 600.degree. C. In some
embodiments, the composite material is quenched by oil. In some
embodiments of the present invention, a solid solution treatment is
performed to the composite material for good ductility.
[0238] In some embodiments, the oil used for quenching is selected
from the following:
[0239] 1. Straight oils are non-emulsifiable products used in
machining operations in an undiluted form. They are composed of
base mineral or petroleum oils, and often contain polar lubricants
like fats, vegetable oils, and esters, as well as extreme pressure
additives such as chlorine, sulfur, and phosphorus. Straight oils
provide the best lubrication and the poorest cooling
characteristics among the quenching fluids. They are also generally
the most economical.
[0240] 2. Water soluble and emulsion fluids are highly diluted
oils, also known as high-water content fluids (HWCF). Soluble oil
fluids form an emulsion when mixed with water. The concentrate
consists of a base mineral oil and emulsifiers to help produce a
stable emulsion. These fluids are used in a diluted form with
concentrations ranging from 3% to 10%, and provide good lubrication
and heat transfer performance. They are used widely in industry and
are the least expensive among all quenching fluids. Water-soluble
fluids are used as water-oil emulsions or oil-water emulsions.
Water-in-oil emulsions have a continuous phase of oil, and superior
lubricating and friction reduction qualities (i.e. metal forming
and drawing). Oil-water emulsions consist of droplets of oil in a
continuous water phase and have better cooling characteristics
(i.e. metal cutting fluids and grinding coolants).
[0241] 3. Synthetic or semi-synthetic fluids or greases are based
on synthetic compounds like silicone, polyglycol, esters, diesters,
chlorofluorocarbons (CFCs), and mixtures of synthetic fluids and
water. Synthetic fluids tend to have the highest fire resistance
and cost. They contain no petroleum or mineral oil base, but are
instead formulated from organic and inorganic alkaline compounds
with additives for corrosion inhibition. Synthetic fluids are
generally used in a diluted form with concentrations ranging from
3% to 10%. They often provide the best cooling performance among
all heat treatment fluids. Some synthetics, such as phosphate
esters, react or dissolve paint, pipe thread compounds, and
electrical insulation. Semi-synthetic fluids are essentially a
combination of synthetic and soluble petroleum or mineral oil
fluids. The characteristics, cost, and heat transfer performance of
semi-synthetic fluids fall between those of synthetic and soluble
oil fluids.
[0242] 4. Micro-dispersion oils contain a dispersion of solid
lubricant particles such as PTFE (Teflon.RTM.), graphite, and
molybdenum disulfide or boron nitride in a mineral, petroleum, or
synthetic oil base. Teflon.RTM. is a registered trademark of
DuPont.
[0243] In some embodiments, the oil used for quenching is held at
room temperature. Other oil temperatures are suitable for the
quenching process as known in the art. In some embodiments,
alternative quenching conditions are used. For example and in one
embodiment, quenching can be conducted in still air, using air
blast, in water at 60-90 degree C. (e.g. for Mg alloy QE22A), or in
30% glycol at room temperature.
Uses of Composites of the Invention
[0244] In one embodiment, metal alloy composites of this invention
are used in the "4C" industry (Computer, Communications, Consumer
Electronics and Car) and for the aerospace industry. In one
embodiment, metal alloy composites of this invention are used in
medical devices (such as consumable (biodegradable) medical
implants), are used for construction, for military devices and
systems, for sports and recreation devices and apparatuses etc. In
one embodiment, composite materials of this invention are used for
ship (marine) construction, for bicycle manufacturing, wheelchair
construction, food packaging, etc.
Definitions
[0245] The term "nanomaterial" refers to matter or material having
at least one dimension in the nanometric range. Within the context
of the present invention, a nanomaterial is meant to have at least
one dimension being of up to 500 nm. Namely, when the nanomaterial
is of particulate form, the average diameter of the particles is up
to 500 nm; in other cases, when the nanomaterial is, for example, a
nanotube, the diameter of the nanotubes is up to 500 nm. In one
embodiment, inorganic layered structures of this invention are
inorganic layered nanostructures. Inorganic layered nano structured
materials are nano materials. In one embodiment, the layered nano
structures of this invention are nanomaterials.
[0246] The term layered nanostructure is meant to encompass a
structure comprising at least one layer, having at least one
dimension in the nanometric range (typically having a thickness of
between 0.1 and 250 nm or between 0.1 and 100 nm or between 0.1 and
10 nm). Such nanostructure may be, by some embodiments, selected
from a sheet, a distorted sheet, a nano-platelet, a spherical or
quasi-spherical nanoparticle, or a tubular nanostructure (e.g.
nanotube, nanoscroll). Nanoplatelets are made of 1-50 layers of an
inorganic layered nanostructure (e.g. MoS.sub.2 nanoplatelet) which
resemble a deck of cards. The nano-platelets can be up to a few
microns wide and have thickness of up to 100 nm. In one embodiment,
the nano-platelet comprises a flat or slightly curved or moderately
curved structure comprising a stack of layers.
[0247] In some embodiments wherein the nanomaterial, or the layered
nano structure, is in the form of a substantially two-dimensional
sheet, the layers may be stacked along a direction perpendicular to
surface of the structure. While the atoms within each layer are
held by strong chemical bonds, weak van der Waals and/or charge
transfer interactions hold the first and second layers together.
The term distorted sheet refers, within the context of the present
disclosure, to a sheet having at least one portion which is curved
(i.e. concaved or convexed) or folded.
[0248] In some embodiments where the layered nanostructure is a
tubular nanostructure, the nano structure may be a nanotube and/or
a nanoscroll.
[0249] The term nanotube denotes an elongated tubular structure
composed of discrete closed layer(s), i.e. each layer is
substantially devoid of dangling, edge bonding sites. Such
nanotubes may be selected in a non-limited fashion from
single-walled nanotubes, multi-walled nanotubes, double-walled
nanotubes, few-walled nanotubes, etc.
[0250] In one embodiment, single-walled nanotube means a nanotube
comprising a single layer of e.g. WS.sub.2.
[0251] The term nanoscroll refers to a single, continuous sheet,
which is rolled onto itself to form a tubular structure. The sheet
may be rolled once, twice or a plurality of times about a
longitudinal axis of the nanoscroll, thereby forming a single,
double or multi-walled nanoscroll, respectively. Therefore, a
nanoscroll of the invention may be formed out of a continuous sheet
having, for example, a single-walled or a multi-walled layered
structure.
[0252] In some embodiments, the diameter of the tubular
nanostructures of the invention is between about 20 and about 500
nm. In some embodiments, the diameter of the tubular nanostructure
is between 0.1 nm and 500 nm, between 1 nm and 500 nm, 1 nm and 100
nm, 10 nm and 500 nm, 10 nm and 100 nm, 20 and 450 nm, between 20
and 400 nm, between 20 and 350 nm, between 20 and 300 nm, between
20 and 250 nm, between 20 and 200 nm, between 20 and 150 nm, or
even between 20 and 100 nm. In some embodiments, the diameter of
the tubular nano structure is between about 25 and about 500 nm,
between about 50 and about 500 nm, between about 100 and about 500
nm, between about 150 and about 500 nm, between about 200 and about
500 nm, between about 250 and about 500 nm, or even between about
300 and about 500 nm. In additional embodiment, the diameter of the
tubular nanostructure is between about 25 and about 400 nm, between
about 50 and about 350 nm, or between about 100 and about 250
nm.
[0253] In one embodiment, the diameter ranges mentioned herein
above are also applicable to spherical or quasi-spherical layered
inorganic nanoparticles.
[0254] In one embodiment, composites of this invention and methods
of producing thereof are not restricted to metal-alloy composites
comprising the inorganic layered nanostructures. Composites of this
invention may also comprise pure metals reinforced by the inorganic
layered nano structures, wherein the metal-composites are formed
similarly to the metal-alloy composites as described herein above.
According to this aspect and in one embodiment, the composites
comprise one metal and at least one inorganic layered
nanostructure. The amount of the inorganic layered nano structure
in the metal composite is much smaller than the amount of the metal
according to such embodiments. According to this aspect and in one
embodiment, the composites consist of one metal and at least one
inorganic layered nanostructure. The amount of the inorganic
layered nanostructure in the metal composite is much smaller than
the amount of the metal according to such embodiments.
[0255] In the metal-composites described herein above, some metal
impurities may be unintentionally present. Such impurities do not
affect the properties of the metal-composites in one
embodiment.
[0256] Moreover, non-metallic solid materials may be reinforced by
inorganic layered nano structures of this invention. Such
reinforced materials may include glasses and alumina-based
materials.
[0257] The term quenching refers to rapid cooling of the material
as known in the art. In one embodiment, the material that was kept
at an elevated temperature is rapidly cooled by e.g.
inserting/placing or dropping the material in/into a liquid
possessing a lower temperature. The temperature of the liquid is
usually much lower than the temperature of the material thus
effectively and rapidly cooling the material.
[0258] Gravity casting (GC) comprises casting using gravity to fill
(e.g. slurry into) the mold.
[0259] The term reinforcement refers to the inorganic layered
nanostructured material. The term reinforcement is interchangeable
with the term inorganic layered nanostructured material. This term
is used in order to emphasize the reinforcement effect of the
inorganic layered nanostructured material on the metal or on the
metal-alloy to which it is added in processes of this
invention.
[0260] MWCNT refers to multiwall carbon nanotubes.
[0261] The foregoing outlines features of several embodiments so
that those skilled in the art may better understand the aspects of
the present disclosure. Those skilled in the art should appreciate
that they may readily use the present disclosure as a basis for
designing or modifying other processes and structures for carrying
out the same purposes and/or achieving the same advantages of the
embodiments introduced herein. Those skilled in the art should also
realize that such equivalent constructions do not depart from the
spirit and scope of the present disclosure, and that they may make
various changes, substitutions, and alterations herein without
departing from the spirit and scope of the present disclosure.
[0262] In one embodiment, the term "a" or "one" or "an" refers to
at least one. In one embodiment the phrase "two or more" may be of
any denomination, which will suit a particular purpose. In one
embodiment, "about" or "approximately" may comprise a deviance from
the indicated term of +1%, or in some embodiments, -1%, or in some
embodiments, .+-.2.5%, or in some embodiments, .+-.5%, or in some
embodiments, .+-.7.5%, or in some embodiments, .+-.10%, or in some
embodiments, .+-.15%, or in some embodiments, .+-.20%, or in some
embodiments, .+-.25%.
EXAMPLES
Example 1
Materials
[0263] The Mg-alloy used for this example was AZ31 with .about.3.0
at % aluminum--available commercially (Taiwan Mach Technology
(LINYI) Co.). The chemical composition of the alloy cited by the
manufacturer is presented in Table 11.
TABLE-US-00011 TABLE 11 Chemical composition (in wt %) of the AZ31
alloy (Mg is about 94.5 wt %). Elements Al Zn Mn Si Fe Cu Ni Mg wt
% 3.08 0.908 0.393 0.022 0.001 0.002 0.01 Balance
[0264] The WS.sub.2 nanotubes were produced by the reaction of
slightly reduced WO.sub.3 nanoparticles with H.sub.2S at
temperatures between 850-900.degree. C. using a fluidized bed
reactor, (i.e. a vertical reactor where the reacting powder is
fluidized (levitated) by a streaming upwards of gas, such as
nitrogen, in addition to the reactive gasses, i.e. H.sub.2S and
H.sub.2).
Example 2
Preparation of Mg MMC Comprising Inorganic Nanotube
[0265] The AZ31 and the WS.sub.2 nanotubes were placed inside a
graphite crucible and heated to 400.degree. C. in a
resistance-heating furnace for 15 minutes; then a stirring vane was
applied; meanwhile, CO.sub.2 and SF.sub.6 gasses were bubbled into
the crucible to help mixing the melt. The CO.sub.2 and the SF.sub.6
gasses were also helpful in preventing oxidation of the melt by
residual water and air. After that, the melt was heated up to
600.degree. C. for 15 minutes. The crucible was further heated
gradually up to 700-720.degree. C., with the molten alloy being
stirred with a vane operated at 350 rev/min for 3 minutes. Finally,
the composite melt was poured into a metallic mold. The Mg MMCs
containing nanotubes with weight fraction of 0.1-1 wt % (see Table
12) were now ready for further mechanical testing. Each composition
was repeated at least three times. Initially, blade stifling ("a"
in Table 12) was used for mixing the nanotubes in the metal melt.
However, due to the small size of the crucible, the blade propeller
led to vortices and non-uniform mixing of the nanotubes in the Mg
MMC. Therefore in the later preparations, the blade stirrer was
replaced by a rod stirrer ("b" in Table 12).
TABLE-US-00012 TABLE 12 Specimens used for this study and their
notation (*x indicates the No. of the specimen with the same
material constituent). wt % of Blade (a) or rod (b) Notation Matrix
INT-WS.sub.2 stirring AZ31-x* AZ31 0 x = 1&2 (a); 3&4 (b)
AZ31INT0.1-x AZ31 0.1 x = 1-3 (a) AZ31INT0.5-x AZ31 0.5 x = 1-3 (b)
AZ31INT1-x AZ31 1 x = 1-3 (b)
[0266] To accommodate for the relatively small amounts of available
WS.sub.2 nanotubes (in total less than 20 g), the melt-stirring
reactor was modified in the present example. A schematic rendering
of the reactor with the gas supply lines is shown in FIG. 2A. FIG.
2B shows a schematic view of the stainless steel crucible used for
melting of the AZ31 alloy. To minimize the amount of the nanotubes
used and allow larger number of samples to be prepared and tested,
the container of the melt was modified so that ingot sizes of app.
100 g could be fabricated. A picture of a few ingots obtained after
the melt stirring at different temperatures is shown in FIG. 2C.
Noticeably, the ingots which were prepared at temperatures of
700.degree. C. and above looked more uniform compared to those
prepared at lower temperatures. One major challenge for this study
was the need to protect the reactive mixture, and especially the
nanotubes, against high-temperature oxidation.
Example 3
Analysis of Mg MMC Comprising Inorganic Nanotube
[0267] A vertical theta-theta diffractometer (TTRAX III, Rigaku,
Japan) equipped with a rotating Cu anode operating at 50 kV and 240
mA was used for XRD studies. The following electron microscopes
were used in this work: SEM model LEO model Supra, 7426. The SEM
was equipped with EDS system model Oxford INCA. TEM (Philips CM120
TEM) operating at 120 kV was equipped with an EDS detector
(EDAX-Phoenix Microanalyzer). For electron microscopy and analysis,
the collected powder was sonicated in ethanol and placed on a
carbon-coated Cu grid (for TEM).
[0268] For the mechanical testing, an MTS Model 458 axial/torsional
testing systems was used according to standard ASTM B 557M-02a
(Standard Test Methods of Tension Testing Wrought and Cast
Aluminum- and Magnesium-Alloy Products).
[0269] For analysis, samples (5.times.5.times.3 mm.sup.3) were cut
from the top, middle and bottom of the ingot. Minute oxidation of
the top and bottom surfaces was unavoidable, but was limited to the
top surface layer of the specimen (few microns), only. X-ray
diffraction (XRD) patterns of the prepared MMC (AZ31INT0.5) are
shown in FIG. 3. A small reflection peak from the (002) plane of
the INT at 13.91.degree. (interlayer spacing of 6.36 .ANG.) is
shifted with respect to bulk 2H-WS.sub.2. This downshift represents
a 2-3% expansion in the interlayer spacing and is attributed to
relaxation of the strain in the nanotubes. This lattice expansion
was attributed to strain relaxation of the WS.sub.2 layers in the
nanotubes. Furthermore, the slightly larger swelling of the
interlayer spacing in the present case could be attributed to Mg
intercalation between the WS.sub.2 layers. It is nevertheless not
clear if the Mg intercalation occurred within the nanotubes or into
portion thereof, which exfoliated during the processing. More
careful inspection of some of the XRD patterns reveals two extra
peaks at 30.degree. and 35.degree. in the MMC (darker curve). The
peak at 30.degree. can be possibly assigned to the compound
Al.sub.2CO, which is formed by the high temperature reaction
between aluminum and the CO.sub.2.
[0270] Scanning electron microscopy (SEM) combined with energy
dispersive X-ray spectroscopy (EDS) was carried out for the
different MMC samples. The carbon content of the analyzed samples
was larger than 10 at % in most cases. This contamination could be
attributed to the CO.sub.2 gas used for the high-temperature
processing of the MMC in the melt-stirring process. A
high-temperature reaction between the magnesium, residual oxygen
and the CO.sub.2 gas could lead to the formation of MgCO.sub.3
phase. This deposit could explain the presence of both carbon and
oxygen in appreciable amounts in the alloy (mainly on the surface).
Oxygen was also present in significant amounts (5-10 at %) and
could reflect the great sensitivity of the samples to surface
oxidation (MgO). Table 13 shows a typical EDS analysis of a
specimen with 0.5 wt % WS.sub.2. The analysis was made over a large
surface area of 1.times.2 mm.sup.2 thus representing a considerable
surface averaging.
TABLE-US-00013 TABLE 13 Results of the EDS analysis of sample
AZ31INT0.5-2 and AZ31INT0.5-3 (excluding carbon and oxygen). "2"
refers to sample 2 (having the same constituents of AZ61, 0.5 wt %
INT); "3" refers to sample 3 (having the same constituents of AZ61,
0.5 wt % INT). AZ31INT0.5-2 AZ31INT0.5-3 Element wt % at % wt % at
% Mg K 96.15 96.82 94.93 97.33 Al K 3.35 3.04 1.63 1.51 W M 0.58
0.08 0.60 0.08 Zn K 0.20 0.07 0.59 0.22 Si K 0.25 0.22 S K 0.35
0.27 0.02 0.02 Fe K 0.02 0.01 Total 100.00 100.00 100.00 100.00
[0271] The EDS analysis showed small non-uniformities in the
tungsten content. However, overall the tungsten content was in most
cases not far from the value of 0.5 wt % of the added amounts of
the nanotubes. However, the sulfur to tungsten atomic ratio was in
most cases smaller than the expected one--1:2. The reduced sulfur
content in the MMC reflected possibly partial oxidation of the
nanotubes during the high-temperature melt-stirring process. It
reflected possibly also the limited inaccuracy of the method at
such small sulfur concentrations.
Example 4
Mechanical Properties of Mg MMC Comprising Inorganic Nanotubes
[0272] Numerous tensile tests were carried out for the AZ31INT
samples. FIG. 4 shows a typical result of such tests for the AZ31
alloy filled with 1 wt % INT-WS.sub.2. Two obvious conclusions can
be drawn from this figure: 1. there exists some scattering in the
data, which therefore necessitated to average over many repetitive
measurements. 2. The addition of the nanotubes had relatively minor
effect on the stiffness and yield strength of the samples, but had
a remarkable advantageous effect on the tensile strength and the
strain (elongation) and consequently on the fracture toughness of
the MMCs (see Table 14). Notwithstanding the scattering in the
data, a reproducible and significant improvement in the fracture
toughness of the Mg-MMCs with addition of minute amounts of
WS.sub.2 nanotubes was confirmed. FIG. 5 presents a summary of the
mechanical properties of the pure alloy and the WS.sub.2
nanotubes-based MMCs after averaging. Indeed, the addition of small
amounts of INT-WS.sub.2, with no additional mechanical processing,
leads to significant improvements in the mechanical behavior of the
Mg-alloy (AZ31). In particular, both the strength and strain of the
MMC was ameliorated, which produced a remarkable improvement in its
fracture toughness.
TABLE-US-00014 TABLE 14 Fracture toughness of the pure AZ31
Mg-alloy and the INT-WS.sub.2 (1 wt %)-Mg-alloy composites.
Toughness [MPa] % change AZ31-4 13.1 -- AZ31INT1-1 38.1 190
AZ31INT1-2 15.3 17 AZ31INT1-3 48.8 272 AZ31INT1-avg. 34.1 160
Example 5
Metallographic Analysis of Mg MMC Comprising Inorganic
Nanotubes
[0273] In order to elucidate the reinforcement effect of the
nanotubes, metallographic analysis was carried-out for the MMCs.
FIG. 6 shows a typical optical micrograph of the surface of three
AZ31INT1 samples and pure AZ31 alloy. Visibly the
nanotubes-containing MMC possess smaller grains. The results of the
grain-size analyses are shown in the block diagrams in FIG. 7A. It
is clear from this figure that the addition of small amounts of
INT-WS.sub.2 to the Mg-MMCs leads to substantial reduction in their
average grain-sizes. Also noticeable is the fact that the average
grain size of the different AZ31INT1 samples (AZ31INT1, 1-3) is
similar (app. 70 microns). This observation suggests that the
nanotubes are uniformly distributed in the Mg-MMC matrix. Finally,
metallographic analysis of quite a few MMCs surfaces, with
different nanotubes content, is displayed in the block diagram in
FIG. 7B. Accordingly, as the nanotubes concentration goes-up the
grain size is reduced. This analysis strongly suggests a
relationship between the grain-size and the mechanical properties
of the MMCs. Seemingly therefore; the nanotubes play the role of
nucleation centers which lead to the diminution of the grain size
of the MMC during solidification. It is not clear at present time,
if the nanotubes are distributed evenly through the bulk of the
grain or they segregate to the grain boundaries between the
different grains. Remarkably also, the error bars, which are
representative of the statistical analysis of the grain size
diminish with the addition of increasing amounts of nanotubes to
the Mg alloy. This fact suggests that the nanotubes induce much
more uniform nucleation of the grains in the Mg-alloy, as compared
to the pure one.
Example 6
Formation of Mg MMC Comprising Layered Inorganic Material by Alloy
Heating Followed by Addition of Layered Inorganic Structures
[0274] In the following description, the AZ31 Mg-based composite
material under the T4 solid solution heat treatment is represented
as "AZ31-T4," while the AZ61 Mg-based composite material under the
T4 solid solution treatment is represented as "AZ61-T4."
[0275] Reference is now made to FIGS. 10A through 10C and FIGS. 11A
through 11C, which respectively illustrates X-ray diffraction
patterns of AZ31-T4 and AZ61-T4 and added with none or with 0.2 wt
% WS.sub.2. Wherein the middle portion and the bottom portion of
the specimen added with 0.2 wt % WS.sub.2 are taken for
measurement. Wherein, FIG. 10B and FIG. 10C are a partial enlarged
image of FIG. 10A (between angle 36.degree. and 38.degree. and
between angles 57.degree. and 58), while FIG. 11B and FIG. 11C are
a partial enlarged image of FIG. 11A (between angle 36.degree. and
38.degree. and between angle 63.degree. and 64.degree.). As
observed from FIG. 10A, the middle portion of the AZ31-T4 added
with 0.2 wt % WS.sub.2 (labeled as "1002") and the bottom portion
of the AZ31-T4 added with 0.2 wt % WS.sub.2 (labeled as "1003")
provide a very weak signal of the WS.sub.2 strengthen phase but a
better signal at (101) between 36.degree. and 37.degree.,
relatively stronger than other peaks and higher than (1001) of
AZ31-T4, which indicates that the crystallinity at (101) is better.
Similar phenomena occurs at (1111) of AZ61-T4 in FIG. 11A, the
middle portion of the AZ61-T4 added with 0.2 wt % WS.sub.2 (labeled
as "1112"), and the bottom portion of the AZ61-T4 added with 0.2 wt
% WS.sub.2 (labeled as "1113"). Reference is now made to FIG. 10B
and FIG. 11B again, which is an enlarged image of the peak (101) at
an angle between 36.degree. and 38.degree. for comparison. It can
be observed that the 2-theta value of peak (1001) of AZ31-T4 and
peak (1111) of AZ61-T4 after added 0.2 wt % WS.sub.2 increases
significantly, as shown in "1002", "1003", "1112", and "1113",
which makes the 2-theta value of the peak shift to the right with a
shifting degree of 0.08. Furthermore, as shown in FIG. 10C and in
FIG. 11C, the peak in the high angle region (between 57.degree. and
58.degree. in FIG. 10C and between 63.degree. and 64.degree. in
FIG. 11C) also shifts to the right with a shifting degree of 0.12,
which proves that the solid solution does occur. When solid
solution occurs, the Mg atoms in the lattice are replaced by S
atoms or W atoms. This causes lattice shrinkage, decreasing the
inter-atom distance (i.e. decreasing the distance between crystal
planes) that causes inter-reaction between interior dislocations
and crew dislocations to enhance the hardness. It should be noticed
that, after solid solution treatment, there is still an amount of
WS.sub.2 strengthen phase, such as the aforementioned 2H-phase
WS.sub.2 strengthen phase, remaining in the metal alloy matrix. By
adjusting the temperature and duration of the solid solution
treatment, the ratio of the WS.sub.2 strengthen phase not dissolved
into the matrix to obtain the ideal mechanical properties and
ductility.
[0276] Please refer to FIGS. 12A through 12F and FIGS. 13A through
13F, which respectively illustrate the metallographic photos of
AZ31 and AZ61 Mg-based composite material added with different
weight percentage of the reinforcement before and after the solid
solution treatment. It should be noticed that WS.sub.2
reinforcement will form the aforementioned WS.sub.2 strengthen
phase in the composite material. Wherein, FIG. 12A, FIG. 12B, and
FIG. 12C respectively represents AZ31 Mg-based composite material
without solid solution treatment and added with none, 0.1 wt %, and
0.2 wt % WS.sub.2. While FIG. 12D, FIG. 12E, and FIG. 12F
respectively represents AZ31 Mg-based composite material with solid
solution treatment and added with none, 0.1 wt %, and 0.2 wt %
WS.sub.2. Similarly, FIG. 13A, FIG. 13B, and FIG. 13C respectively
represents AZ61 Mg-based composite material without solid solution
treatment and added with none, 0.1 wt %, and 0.2 wt % WS.sub.2.
While FIG. 13D, FIG. 13E, and FIG. 13F respectively represents AZ61
Mg-based composite material with solid solution treatment and added
with none, 0.1 wt %, and 0.2 wt % WS.sub.2.
[0277] In FIGS. 12A through 12C, there is a .beta. phase
(Mg.sub.17Al.sub.12) of AZ series alloys located at the grain
boundary, which will decrease the ductility of the Mg-based
composite material. The metallographic photos of Mg-based composite
material after solid solution treatment, as shown in FIGS. 12D
through 12F, obviously show the shape and size of the grains, and
most of the .beta. phase that is dissolved into the grains instead
of existing at grain boundary. Similar phenomena occur in AZ61
Mg-based composite material (as shown in FIGS. 13A through 13F),
despite that the Al content in AZ61 is higher so that the amount of
the .beta. phase is higher than that of AZ31.
[0278] The average grain sizes of various Mg-based composite
material ingots (AZ31-T4 and AZ61-T4) with different additive
amount of the reinforcement are discussed in the following. It
should be noticed that WS.sub.2 reinforcement will form the
aforementioned strengthening phase of WS.sub.2 in the composite
materials. The grain sizes are calculated by linear intercept
method and are summarized in Table 15 as shown below.
TABLE-US-00015 TABLE 15 average grain sizes of various Mg-based
composite materials with different additive amount of WS.sub.2.
WS.sub.2 0 wt % 0.1 wt % 0.2 wt % AZ31-T4 80.0 .mu.m 55.0 .mu.m
40.0 .mu.m AZ61-T4 51.7 .mu.m 37.5 .mu.m 31.8 .mu.m
[0279] As evident from Table 15, the average grain size of the AZ31
undergoing the T4 treatment is 80.0 .mu.m. When the AZ31-T4 Mg
alloy is added with 0.1 wt % WS.sub.2, the average grain size
decreases into 50 .mu.m (37.5% decrease). When further increasing
the adding content of WS.sub.2 of the AZ31-T4 Mg alloy up to 0.2 wt
%, the average grain size further decreases into 40 .mu.m (50%
decrease). On the other hand, the average grain size of the AZ61
undergoing the T4 treatment is 51.7 .mu.m. When the AZ61-T4 Mg
alloy is added with 0.1 wt % WS.sub.2, the average grain size
decreases into 37.5 .mu.m (27.5% decrease). When further increasing
the adding content of WS.sub.2 of the AZ61-T4 Mg alloy up to 0.2 wt
%, the average grain size further decreases into 31.8 .mu.m (38.5%
decrease). Wherein, since the AZ61 includes higher content of Al,
which will restrain the grain growth, the average grain size of the
AZ61-T4 is smaller than the AZ-31-T4. Furthermore, adding the
reinforcement into the metal alloy matrix, which will forms the
aforementioned strengthen phase in the composite material), makes
the metal alloy matrix have more nucleation points during the
casting process, which will restrain grain growth and forms more
smaller grains in a specific volume.
[0280] The invention further perform Vickers-hardness test to
Mg-base composite material ingots. The Vickers-hardness (HV) of
AZ31-T4 and AZ61-T4 composite materials with different additive
amount of WS.sub.2 are summarized in Table 16 as shown below.
TABLE-US-00016 TABLE 16 Vickers-hardness of various Mg-based
composite materials with different additive amount of WS.sub.2.
WS.sub.2 0 wt % 0.1 wt % 0.2 wt % AZ31-T4 51.0 HV 54.3 HV 55.9 HV
AZ61-T4 55.4 HV 58.3 HV 58.6 HV
[0281] As shown in Table. 16, the hardness of the AZ31-T4 Mg-based
composite material without reinforcement is 51.0 HV, while the
hardness of the AZ31-T4 Mg-based composite material added with 0.1
wt % WS.sub.2 is 54.3 HV (6.5% increase). When further increasing
the adding content of WS.sub.2 of the AZ31-T4 Mg-based composite
material up to 0.2 wt %, the hardness further increases to 55.9 HV
(9.6% increase). On the other hand, the hardness of the AZ61-T4
Mg-based composite material without reinforcement is 55.4 HV, while
the hardness of the AZ61-T4 Mg-based composite material added with
0.1 wt % WS.sub.2 is 58.3 HV (5.2% increase). When further
increasing the adding content of WS.sub.2 of the AZ61-T4 Mg-based
composite material up to 0.2 wt %, the hardness further increases
to 58.6 I-TV (5.8% increase). Since the content of Al in the
AZ61-T4 is higher than that of the AZ31-T4, the precipitated
brittle .beta. phase in the AZ61-T4 is also higher than that of the
AZ31-T4. Thus, the hardness of the AZ61-T4 without reinforcement
added is higher than that of the AZ31-T4 without reinforcement
added. Moreover, as known from the aforementioned Table 15, adding
of the reinforcement such as WS.sub.2 will decrease the grain size
and causes grain strengthen effect. Therefore, the hardness of the
Mg-based composite material added with 0.2 wt % WS.sub.2 is higher
than that of the Mg-based composite material added with 0.1 wt %
WS.sub.2.
[0282] Besides the aforementioned Vickers-hardness test, the
invention further uses a tension test for discussing the influence
of additive amount of the reinforcement on mechanical properties of
AZ31-T4 and AZ61-T4 Mg-based composite material. After the
aforementioned gravity mold casting process and T4 solid solution
process, both AZ31-T4 and AZ61-T4 Mg-based composite materials are
made into specimens according to ASTM E8-69. Each of the specimens
has a gage width (GW) equals to 6 mm, a gage length (GL) equals to
13 mm and a holding length (HL) equals to 12 mm, and the total
length of the specimen equals to 45 mm. Then, a tension test is
performed on the specimen with a tension speed equals to 1 mm/min
by a MTS testing machine. Each group of the Mg-based composite
materials is measured 5 times and the average value is calculated.
Thus, mechanical properties of different AZ31-T4 and AZ61-T4
composite materials with different additive amount of WS.sub.2 are
compared and summarized in Table 17 as shown below.
TABLE-US-00017 TABLE 17 mechanism properties of Mg-based composite
materials with different additive amount of WS.sub.2. Mg-based
Ultimate Tensile composite WS.sub.2 Yield Strength Strength
Elongation material (wt %) (MPa) (MPa) (%) AZ31-T4 0 74.8 134.8
13.90 0.1 85.7 171.7 23.42 0.2 87.2 208.2 25.74 AZ61-T4 0 76.8
130.4 10.0 0.1 79.8 157.3 19.08 0.2 85.4 188.7 19.62
[0283] As shown in Table 17, the yield strength, the ultimate
tensile strength, and the elongation of either the AZ31-T4 or the
AZ61-T4 can be increased simultaneously and significantly by adding
small amount of WS.sub.2. The yield strength, the ultimate tensile
strength, and the elongation of the AZ31-T4 added with 0.2 wt % of
WS.sub.2 are 87.2 MPa, 208.2 MPa, and 25.74% respectively. While
the yield strength, the ultimate tensile strength, and the
elongation of the AZ61-T4 added with 0.2 wt % of WS.sub.2 are 85.4
MPa, 188.7 MPa, and 19.62% respectively. The yield strength, the
ultimate tensile strength, and the elongation of the AZ31-T4
increase 40.1%, 15.9%, and 110.0% respectively. While, the yield
strength, the ultimate tensile strength, and the elongation of the
AZ61-T4 increase 30.1%, 6.0%, and 144.9% respectively. In the
aspect of mechanical strengths, since the content of Al in AZ61 is
higher than that in AZ31, there is more .beta. phase at grain
boundary in AZ61, which decreases the number of initial points of
uneven cracks during the stretching test. Therefore, the mechanical
strength of AZ31-T4 is higher than that of the AZ61-T4. On the
other hand, the reasons of increasing the mechanical strength of
the Mg-based composite material after adding the reinforcement are
increasing dislocation density, grain refinement, and the loading
shift of stress.
[0284] In the aspect of the ductility, both AZ31-T4 and AZ61-T4
show an increasing trend after adding the reinforcement. It is
because that, after adding the reinforcement into the metal alloy
matrix, grain size decreases, WS.sub.2 strengthen phase distributes
more homogeneously, and additional nonbasal slip systems are
provided, increases ductility. Furthermore, since the AZ31-T4 has
less brittle phase, it has higher ductility than that of the
AZ61-T4.
[0285] The AZ31 and AZ61 Mg-based composite material made through
the gravity casting method of the present disclosure and go through
T4 solid solution treatment have excellent mechanical properties.
After adding the WS.sub.2 reinforcement into the AZ31-T4 and the
AZ61-T4, the formed WS.sub.2 strengthen phase makes the hardness,
tensile strength, and the elongation improved significantly. The
ultimate tensile strength, the yield strength, the elongation, and
the hardness of the AZ31-T4 Mg-based composite material added with
0.2 wt % WS.sub.2 are 208.2 MPa, 87.2 MPa, 25.7%, 55.9 HV
respectively, which are 54.5%, 16.6%, 85.2%, 9.6%, and 50.0%
improved respectively compared with the AZ31-T4 without addition of
WS.sub.2. On the other hand, the ultimate tensile strength, the
yield strength, the elongation, and the hardness of the AZ61-T4
Mg-based composite material added with 0.2 wt % WS.sub.2 are 188.7
MPa, 85.4 MPa, 19.6%, 58.6 HV respectively, which are 44.7%, 11.2%,
95.4%, 5.8%, and 38.5% improved respectively compared with the
AZ61-T4 without addition of WS.sub.2.
[0286] While certain features of the invention have been
illustrated and described herein, many modifications,
substitutions, changes, and equivalents will now occur to those of
ordinary skill in the art. It is, therefore, to be understood that
the appended claims are intended to cover all such modifications
and changes as fall within the true spirit of the invention.
* * * * *