U.S. patent application number 15/258724 was filed with the patent office on 2017-03-30 for thermoplastic forming of cold rolled alloys.
The applicant listed for this patent is Apple Inc.. Invention is credited to Hsiang Hung Chen, Naoto Matsuyuki, Kazuya Takagi, Theodore A. Waniuk, Yoshihiko Yokoyama.
Application Number | 20170087610 15/258724 |
Document ID | / |
Family ID | 58406105 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170087610 |
Kind Code |
A1 |
Yokoyama; Yoshihiko ; et
al. |
March 30, 2017 |
THERMOPLASTIC FORMING OF COLD ROLLED ALLOYS
Abstract
The disclosure is directed to methods of forming glassy alloys.
A glassy alloy is cold rolled at a temperature less than Tg of the
glassy alloy to form a flattened glassy alloy. Then, the cold
rolled glassy alloy is thermoplastically formed at a temperature
above Tg of the glassy alloy. In certain embodiments, the flattened
glassy alloy may have one or more shear bands and/or micro-cracks,
and the thermoplastic forming may heal the shear bands and/or
micro-cracks. The resulting glassy alloy may thereby have reduced
or eliminated shear bands and/or micro-cracks.
Inventors: |
Yokoyama; Yoshihiko; (Tokyo,
JP) ; Waniuk; Theodore A.; (Lake Forest, CA) ;
Chen; Hsiang Hung; (New Taipei, CN) ; Takagi;
Kazuya; (Tokyo, JP) ; Matsuyuki; Naoto;
(Kasugai-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Family ID: |
58406105 |
Appl. No.: |
15/258724 |
Filed: |
September 7, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62234743 |
Sep 30, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 5/04 20130101; C22C
45/003 20130101; B21B 3/003 20130101 |
International
Class: |
B21B 3/00 20060101
B21B003/00; C22C 5/04 20060101 C22C005/04; C22C 45/00 20060101
C22C045/00 |
Claims
1. A method of forming a glassy alloy comprising: cold rolling a
glassy alloy feedstock at a temperature less than the glass
transition temperature (Tg) of the glassy alloy feedstock to form a
flattened glassy alloy; and thermoplastically forming the flattened
glassy alloy at a temperature at or above Tg of the glassy alloy
feedstock to form the glassy alloy.
2. The method of claim 1, wherein the glassy alloy has a thickness
that does not vary by more than about 10% after cold rolling and
thermoplastic forming.
3. The method of claim 1, wherein the flattened glassy alloy has a
thickness that is within about 0.04 mm of the thickness of the
glassy alloy.
4. The method of claim 1, wherein the flattened glass alloy
comprises one or more shear bands.
5. The method of claim 4, wherein the thermoplastic forming heals
the one or more shear bands in the flattened glassy alloy to form a
substantially shear band-free glassy alloy.
6. The method of claim 5, wherein less than 2% of the total surface
area of the substantially shear band-free glassy alloy comprises
shear bands.
7. The method of claim 1, wherein the glassy alloy is selected from
a nickel (Ni) based glassy alloy, an iron (Fe) based glassy alloy,
a copper (Cu) based glassy alloy, a zinc (Zi) based glassy alloy, a
zirconium (Zr) based glassy alloy, a gold (Au)-based glassy alloy,
a platinum (Pt) based glassy alloy, and a palladium (Pd) based
glassy alloy.
8. The method of claim 1, wherein the flattened glassy alloy is
thermoplastically formed for 15 to 90 seconds.
9. The method of claim 1, wherein the glassy alloy is a Pt-based
glassy alloy.
10. The method of claim 9, wherein the flattened glassy alloy is
thermoplastically formed for 15 to 30 seconds.
11. A glassy alloy part comprised of a glassy alloy and formed from
a combination of cold rolling and thermoplastic forming, wherein
the glassy alloy part has a variation in thickness of less than
about 10% and is substantially free of shear bands.
12. The glassy alloy part of claim 11, wherein less than 2% of the
total surface area of the glassy alloy part comprises shear
bands.
13. The glassy alloy part of claim 11, wherein the glassy alloy is
selected from a nickel (Ni) based glassy alloy, an iron (Fe) based
glassy alloy, a copper (Cu) based glassy alloy, a zinc (Zi) based
glassy alloy, a zirconium (Zr) based glassy alloy, a gold
(Au)-based glassy alloy, a platinum (Pt) based glassy alloy, and a
palladium (Pd) based glassy alloy.
14. The glassy alloy part of claim 11, wherein the glassy alloy is
a Pt-based glassy alloy.
15. The glass alloy part of claim 11, wherein the glass alloy part
exhibits no structural relaxation embrittlement.
16. A method of determining the presence of a crystalline metal in
a glassy alloy comprising: cold rolling a glassy alloy feedstock at
a temperature less than Tg of the glassy alloy to form a flattened
glassy alloy; and determining the presence of cracks radiating from
a portion of the flattened glassy alloy, the portion of the
flattened glassy alloy corresponding to the presence of the
crystalline metal in the flattened glassy alloy.
17. The method of claim 16, wherein the glassy alloy is selected
from a nickel (Ni) based glassy alloy, an iron (Fe) based glassy
alloy, a copper (Cu) based glassy alloy, a zinc (Zi) based glassy
alloy, a zirconium (Zr) based glassy alloy, a gold (Au)-based
glassy alloy, a platinum (Pt) based glassy alloy, and a palladium
(Pd) based glassy alloy.
18. The method of claim 16, further comprising thermoplastically
forming the flattened glassy alloy at a temperature at or above Tg
of the glassy alloy feedstock to form the glassy alloy.
19. The method of claim 16, wherein the glassy alloy has a
thickness that does not vary by more than about 10% after cold
rolling and thermoplastic forming.
20. The method of claim 19, wherein the thermoplastic forming heals
cracks radiating from a portion of the flattened glassy alloy.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Patent Application No. 62/234,743, entitled
"THERMOPLASTIC FORMING OF COLD ROLLED ALLOYS," filed on Sep. 30,
2015, which is incorporated herein by reference in its
entirety.
FIELD
[0002] The disclosure relates generally to methods for forming of
glassy alloys. More particularly, the disclosure relates to methods
of cold rolling, then for thermoplastic forming, glassy alloys.
BACKGROUND
[0003] Glassy alloys (also referred to herein as amorphous alloys
or metallic glasses) are alloys that do not have a crystalline
structure. Instead, glassy alloys are amorphous. Glassy alloys have
a number of beneficial material properties that make them viable
for use in a number of engineering applications.
[0004] Various methods have been used to process glassy alloys in
an attempt to produce glassy alloy parts. However, viscosities of
glassy alloys are typically above 10.sup.5 Pas. As such, many
traditional methods of processing alloys lead to the formation of
shear bands and/or micro-cracks. For instance, methods of cold
rolling glassy alloys cause shear band formation (i.e.
inhomogeneous deformation) and/or formation of micro-cracks. High
viscosities (10.sup.5-10.sup.7 Pas) in the supercooled liquid
region also create difficulties for the precise formation of
amorphous metal parts from amorphous alloy feedstock using
thermoplastic forming techniques. Neither technique has been
considered viable for manufacturing or forming glassy alloys.
[0005] Precise glassy alloy parts cannot ordinarily be produced
using either method. As a result, glassy alloys can be difficult to
form into parts with predictable thicknesses and shapes for use in
commercial products. The present disclosure addresses these and
other limitations.
SUMMARY
[0006] In certain aspects, the disclosure is directed to methods of
forming a glassy alloys and glassy alloy parts by thermoplastically
forming a cold rolled glassy alloy feedstock.
[0007] In certain embodiments, a glassy alloy feedstock is cold
rolled at a temperature less than Tg (the glass transition
temperature) of the glassy alloy feedstock to form a flattened
glassy alloy. The flattened glassy alloy may then be
thermoplastically formed at a temperature at or above Tg of the
glassy alloy feedstock, e.g., to form a glassy alloy part.
[0008] In certain embodiments, the cold rolled, flattened glassy
alloy may have one or more shear bands. In certain embodiments, the
thermoplastic forming may be used to heal one or more shear bands
in the cold rolled, flattened glassy alloy to form a substantially
shear band-free glassy alloy.
[0009] In certain embodiments, the thermoplastic forming may be
used to form glassy alloy parts with desired properties, such as
desired three-dimensional shapes, desired thickness, desired
bending stress, etc.
[0010] In certain aspects, the glassy alloy part may be comprised
of a glassy alloy and formed from a combination of cold rolling and
thermoplastic forming, wherein the glassy alloy part has a
variation in thickness of less than about 10% and is substantially
free of shear bands.
[0011] In another aspect, the disclosure is directed to methods of
determining the presence of crystalline metal in a glassy alloy.
First, the glassy alloy feedstock is cold rolled at a temperature
less than Tg of the glassy alloy to form a flattened glassy alloy.
The presence of cracks radiating from a portion of the alloy
corresponds to the presence of a crystalline metal.
[0012] Additional embodiments and features are set forth in part in
the description that follows, and will become apparent to those
skilled in the art upon reading of the specification. A further
understanding of the nature and advantages of the present
disclosure can be realized by reference to the remaining portions
of the specification and the drawings, which forms a part of this
disclosure.
BRIEF DESCRIPTION OF THE FIGURES
[0013] Although the following figures and description illustrate
specific embodiments and examples, the skilled artisan will
appreciate that various changes and modifications may be made
without departing from the spirit and scope of the disclosure.
[0014] FIG. 1A depicts side view of as-cast rectangular shaped
glassy alloy having a thickness of about 2 mm.
[0015] FIG. 1B depicts side view of a few percent cold rolled
glassy alloy.
[0016] FIG. 1C depicts side view of 90% cold rolled glassy
alloy.
[0017] FIG. 2 depicts a temperature-viscosity diagram of an
exemplary bulk solidifying metallic glass alloy.
[0018] FIG. 3 depicts a schematic of a
time-temperature-transformation (TTT) diagram for an exemplary bulk
solidifying metallic glass alloy.
[0019] FIG. 4A depicts a graph of plate thickness vs. thickness of
thermoplastic forming for four glassy alloy samples.
[0020] FIG. 4B depicts a thermoplastic pressed plate having
variable thickness throughout.
[0021] FIG. 4C depicts cold rolled ribbon of glassy alloy having
reproducible thickness.
[0022] FIG. 5 shows the bending deflection curves of as-cast glassy
alloys compared to cold rolled/thermoplastic formed Pt850 alloys in
a 3-points bending test.
[0023] FIG. 6A shows the cross-section of a punched glassy alloy
prepared by cold-rolling and thermoplastic forming.
[0024] FIG. 6B depicts an exploded view and lack of undercut
resulting from punching the glassy alloy of FIG. 6A.
[0025] FIG. 6C depicts an exploded view and lack of burr resulting
from punching the glassy alloy of FIG. 6A.
DETAILED DESCRIPTION
[0026] Reference will now be made in detail to representative
embodiments described herein and illustrated in the accompanying
drawings. It should be understood that the following descriptions
are not intended to limit the embodiments to one preferred
embodiment. To the contrary, it is intended to cover alternatives,
modifications, and equivalents as can be included within the spirit
and scope of the described embodiments as defined by the appended
claims.
[0027] In various aspects of the disclosure, cold rolled and
thermoplastically formed glassy alloys and glassy alloy parts can
be formed with higher precision and desired properties. In some
embodiments, cold rolling of glassy alloy feedstock provides
heightened thickness control, while thermoplastic forming heals
shear bands and/or micro-cracks formed during cold rolling of the
glassy alloy feedstock. In some embodiments, the resulting glassy
alloys can have increased strength.
[0028] In certain aspects, the disclosure is directed to methods of
forming glassy alloys and glassy alloy parts by thermoplastically
forming a cold rolled glassy alloy feedstock. In certain
embodiments, a glassy alloy feedstock is cold rolled at a
temperature less than Tg (the glass transition temperature) of the
glassy alloy feedstock to form a flattened glassy alloy. The
flattened glassy alloy may then be thermoplastically formed at a
temperature at or above Tg of the glassy alloy feedstock, e.g., to
form a glassy alloy or glassy alloy part. In certain embodiments,
the cold rolled, flattened glassy alloy may have one or more shear
bands. In certain embodiments, the thermoplastic forming may be
used to heal one or more shear bands in the cold rolled, flattened
glassy alloy to form a substantially shear band-free glassy
alloy.
[0029] In certain aspects of the disclosure, the combination of
cold rolling and thermoplastic forming provides for control of part
thickness, reproducibility, absence of shear bands and/or
micro-cracks, and/or retention of metallic glass properties. For
instance, in certain embodiments, the methods of the disclosure may
be used to form glassy alloy and glassy alloy parts with desired
properties, such as desired three-dimensional shapes, desired
thickness, desired bending stress, etc. In various aspects, the
formed glassy alloy and glassy alloy parts may have, e.g., a
consistent thickness, reduced or eliminated shear bands and/or
micro-cracks. In certain embodiments, the present disclosure
provides for formation of glassy alloy parts without casting or
injection molding.
[0030] In certain aspects, methods of forming glassy alloys and
glassy alloy parts using a combination of cold rolling and
thermoplastic forming are provided. In accordance with the
disclosure, the combination of cold rolling and thermoplastic
forming processes can improve structural integrity of glassy alloys
and glassy alloy parts, as well as reduce or eliminate associated
cosmetic defects such as shear bands and/or micro-cracks. As
described herein, the glassy alloy and glassy alloy parts can be
substantially shear band-free. As used herein, substantially shear
band-free glassy alloy can have less than 2% of the total surface
area of the glassy alloy having shear bands. Alternatively,
substantially shear band-free glassy alloy can have less than 1% of
the total surface area of the glassy alloy having shear bands.
Alternatively, substantially shear band-free glassy alloy can have
less than 0.1% of the total surface area of the glassy alloy having
shear bands. Alternatively, substantially shear band-free glassy
alloy can have less than 0.01% of the total surface area of the
glassy alloy having shear bands. Alternatively, substantially shear
band-free glassy alloy can have no shear bands.
[0031] Any suitable cold rolling method and apparatus/mill known in
the art may be used in connection with the present disclosure. As
understood by those of skill in the art, in accordance with aspects
of the disclosure cold rolling is performed at temperatures below
Tg of the glass metal feedstock. In certain aspects, pressure is
controlled to obtain and maintain the desired thickness tolerance,
as discussed in further detail herein.
[0032] Cold rolling at a temperature below Tg allows glassy alloys
to be processed to have a predictable and precise thickness.
Without wishing to be limited to any particular theory or mode of
action, shear bands and micro-cracks can form when the glassy alloy
is cold rolled due to the stress imparted on the alloy. FIG. 1A
depicts side view of as-cast rectangular shaped glassy alloy having
a thickness of about 2 mm. FIG. 1B shows roughly parallel shear
bands 106 running throughout cold rolled glassy alloy 102. Initial
shear bands were introduced to the glassy alloy. The thickness of
the glassy alloy feedstock was reduced by tilting the shear bands
under cold rolling up to about 30% at the critical point to
introduce second shear bands. A large number of fine and coarse
density shear bands were observed. FIG. 1C depicts a side view of
90% cold rolled glassy alloy showing a micro-crack (open gap of
shear band) 104 formed at the rolled surface of 90% cold rolled
glassy alloy 102. The thickness of the cold rolled glassy alloy had
an accurate and reproducible thickness of about 200 .mu.m.
[0033] In accordance with certain aspects, any suitable
thermoforming technique known in the art may be used in connection
with the present disclosure. As understood by those of skill in the
art, in accordance with methods described herein, during
thermoplastic forming, the flattened, cold rolled glassy alloy is
thermoplastically formed at a temperature above the Tg of the
glassy alloy feedstock, during which there is a substantial drop in
viscosity. As will be recognized by those skilled in the art,
different glassy alloys can be thermoplastically formed for
different periods of time. In certain variations, the period of
time can be 15 seconds, 30 seconds, 45 seconds, 60 seconds, 75
seconds, or 90 seconds. The amount of time can depend on the glassy
alloy.
[0034] In certain embodiments, the combination of cold rolling and
thermoplastic forming provides thickness control. Cold rolling of
glassy alloys alone results in shear bands and/or micro-cracks.
Thermoplastic forming of glassy alloys alone does not result in
predictable or controllable thicknesses. In certain embodiments,
the combination of cold rolling and thermoplastic forming described
herein controls thickness variation (i.e., variation within a
single alloy piece/part and variation between production runs) to
within less than about 10%, less than about 8%, less than about 6%,
less than about 5%, etc. Predictable thickness is particularly
important in glassy alloys that have mechanical properties that
depend on thickness (e.g., leaf springs). The combination of cold
rolling and thermoplastic forming results in predictable and
reproducible formation of glassy alloy thicknesses, and further
materials that have the benefit of glassy alloys. Without wishing
to be limited to a theory or specific mode of action, cold rolling
provides thickness control, and thermoplastic forming provides
shape control, of the resulting metallic glass.
[0035] In certain embodiments, the glassy alloys and glassy alloy
parts of the disclosure can be formed with a predictable and
reproducible shape and thickness using the methods described
herein. In certain embodiments, cold rolling of a glassy alloy
feedstock can provide control of the thickness of a flattened, cold
rolled glassy alloy for use in thermoplastic forming to within a
desired tolerance of, e.g., within about 0.1 mm, about 0.08 mm,
about 0.06 mm, about 0.05 mm, about 0.04 mm, about 0.03 mm, etc.,
of the final thickness of the processed thermoplastic formed glassy
alloy. The thickness of a thermoplastically formed glassy alloy or
glassy alloy part using such a flattened, cold rolled glassy alloy
can thereby be formed with high precision. In addition, by first
cold rolling a glassy alloy and then thermoplastically forming the
cold rolled glassy alloy, the time and load for thermoplastic
forming can be reduced.
[0036] Surprisingly, glassy alloys that are cold rolled and then
thermoplastically formed as described herein do not become brittle,
and in some instances can become stronger while shear bands relax
and micro-cracks diminish. Again without wishing to be limited to a
particular mechanism or mode of action, glassy alloy atoms heated
above the Tg of the glassy alloy relax. In most glassy alloys, this
results in embrittlement and loss of properties such as strength.
If the glassy alloy is thermoplastically formed for a certain
period of time (e.g., 15 s to 90 s), the lack of embrittlement can
also be accompanied by increased strength.
[0037] The cold rolled and thermoplastically formed glassy alloys
can be processed subsequent to the thermoplastic forming step to
form parts. Such methods include punching portions from the glassy
alloy, water jet cutting, laser cutting, slitter cutting, or any
other method known in the art.
[0038] In some aspects, the method can be used to fabricate parts,
such as leaf springs, that require a predictable material
thickness. Glassy alloys are believed to deform easily. The
viscosity of supercooled liquid of glassy alloys (e.g. Zr-based
glassy alloys) is on the order of about 10.sup.6 to 10.sup.7 Pas,
and the time for thermoplastic processing of such glassy alloys can
be limited to below 1 minute. Without wishing to be held to a
specific mode or theory of action, using conventional pressing
methods to press a button glassy alloy into a 0.2 mm plate and 2 cm
square with normal press strain rate (10.sup.2) would require a
load of over 40 tons. A die used to compress such a material would
be rendered unusable because the die would elastically deform. The
deformed die subsequently would produce glassy alloy parts with
non-uniform thicknesses. Methods that combine cold rolling and
thermoplastic forming allow formation of glassy alloy structures
such as leaf springs that have a predictable material
thickness.
[0039] Other aspects of the disclosure relate to glassy alloy parts
comprised of a glassy alloy formed from a combination of cold
rolling and thermoplastic forming as described herein. In certain
aspects, the glassy alloy part may have a variation in thickness of
less than about 10%, less than about 8%, less than about 6%, less
than about 5%, etc.
[0040] In other aspects, the glassy metal part may be substantially
free of shear bands. Again, as used herein, substantially shear
band-free glassy alloy can have less than 2% of the total surface
area of the glassy alloy having shear bands. Alternatively,
substantially shear band-free glassy alloy can have less than 1% of
the total surface area of the glassy alloy having shear bands.
Alternatively, substantially shear band-free glassy alloy can have
less than 0.1% of the total surface area of the glassy alloy having
shear bands. Alternatively, substantially shear band-free glassy
alloy can have less than 0.01% of the total surface area of the
glassy alloy having shear bands. Alternatively, substantially shear
band-free glassy alloy can have no shear bands.
[0041] In a further aspect, the disclosure is further directed to
methods of controlling the quality of a glassy alloy. Crystals are
considered defects within a glassy alloy. In various embodiments,
the glassy alloy is cold rolled at a temperature less than Tg of
the alloy to form a flattened glassy alloy. The flattened glassy
alloy is examined for the presence of cracks radiating from a
particular point in the alloy. The presence of cracks radiating
from a point in the alloy determines the presence of a crystal in
the glassy alloy.
[0042] Any glassy alloy in the art may be used in the methods
described herein. As used herein, the terms glassy alloy, metallic
glass alloy, metallic glass-forming alloy, amorphous metal,
amorphous alloy, bulk solidifying amorphous alloy, BMG alloy, and
bulk metallic glass alloy are used interchangeably.
[0043] In various embodiments, the glassy alloy can be a nickel
(Ni) based alloy, iron (Fe) based alloy, copper (Cu) based alloy,
zinc (Zi) based alloy, zirconium (Zr) based alloy, gold (Au)-based
alloy, platinum (Pt) based alloy, palladium (Pd) based alloy, or
any other glassy alloy. Similarly, glassy alloy described herein as
a constituent of a composition or glassy alloy part can be of any
type. As recognized by those of skill in the art, glassy alloys may
be selected based on and may have a variety of potentially useful
properties. In particular, glassy alloys tend to be stronger than
crystalline alloys of similar chemical composition.
[0044] The glassy alloy can comprise multiple transition metal
elements, such as at least two, at least three, at least four, or
more, transitional metal elements. The alloy can also optionally
comprise one or more nonmetal elements, such as one, at least two,
at least three, at least four, or more, nonmetal elements. A
transition metal element can be any of scandium, titanium,
vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc,
yttrium, zirconium, niobium, molybdenum, technetium, ruthenium,
rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten,
rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium,
dubnium, seaborgium, bohrium, hassium, meitnerium, ununnilium,
unununium, and ununbium. In one embodiment, a BMG containing a
transition metal element can have at least one of Sc, Y, La, Al,
Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh,
Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg. Depending on the
application, any suitable transitional metal elements, or their
combinations, can be used.
[0045] Depending on the application, any suitable nonmetal
elements, or their combinations, can be used. A nonmetal element
can be any element that is found in Groups 13-17 in the Periodic
Table. For example, a nonmetal element can be any one of F, Cl, Br,
I, At, O, S, Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and
B. Occasionally, a nonmetal element can also refer to certain
metalloids (e.g., B, Si, Ge, As, Sb, Te, and Po) in Groups 13-17.
In one embodiment, the nonmetal elements can include B, Si, C, P,
or combinations thereof. Accordingly, for example, the alloy can
comprise a boride, a carbide, or both.
[0046] In some embodiments, the glassy alloy composition described
herein can be fully alloyed. The term fully alloyed used herein can
account for minor variations within the error tolerance. For
example, it can refer to at least 90% alloyed, such as at least 95%
alloyed, such as at least 99% alloyed, such as at least 99.5%
alloyed, such as at least 99.9% alloyed. The percentage herein can
refer to either volume percent or weight percentage, depending on
the context. These percentages can be balanced by impurities, which
can be in terms of composition or phases that are not a part of the
alloy. The alloys can be homogeneous or heterogeneous, e.g., in
composition, distribution of elements, amorphicity/crystallinity,
etc.
[0047] The glassy alloy can include any combination of the above
elements in its chemical formula or chemical composition. The
elements can be present at different weight or volume percentages.
Alternatively, in one embodiment, the above-described percentages
can be volume percentages, instead of weight percentages.
Accordingly, a glassy alloy can be zirconium-based, titanium-based,
platinum-based, palladium-based, gold-based, silver-based,
copper-based, iron-based, nickel-based, aluminum-based,
molybdenum-based, and the like. The glassy alloy can also be free
of any of the aforementioned elements to suit a particular purpose.
For example, in some embodiments, the glassy alloy, or the
composition including the glassy alloy, can be substantially free
of nickel, aluminum, titanium, beryllium, or combinations thereof.
In one embodiment, the alloy or the composite is completely free of
nickel, aluminum, titanium, beryllium, or combinations thereof.
[0048] The afore described glassy alloy systems can further include
additional elements, such as additional transition metal elements,
including Nb, Cr, V, and Co. The additional elements can be present
at less than or equal to about 30 wt %, such as less than or equal
to about 20 wt %, such as less than or equal to about 10 wt %, such
as less than or equal to about 5 wt %. In one embodiment, the
additional, optional element is at least one of cobalt, manganese,
zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium
and hafnium to form carbides and further improve wear and corrosion
resistance. Further optional elements may include phosphorous,
germanium and arsenic, totaling up to about 2%, and preferably less
than 1%, to reduce melting point. Otherwise incidental impurities
should be less than about 2% and preferably 0.5%.
[0049] In some embodiments, a composition having a glassy alloy can
include a small amount of impurities. The impurity elements can be
intentionally added to modify the properties of the composition,
such as improving the mechanical properties (e.g., hardness,
strength, fracture mechanism, etc.) and/or improving the corrosion
resistance. Alternatively, the impurities can be present as
inevitable, incidental impurities, such as those obtained as a
byproduct of processing and manufacturing. The impurities can be
less than or equal to about 10 wt %, such as about 5 wt %, such as
about 2 wt %, such as about 1 wt %, such as about 0.5 wt %, such as
about 0.1 wt %. In some embodiments, these percentages can be
volume percentages instead of weight percentages. In one
embodiment, the glassy alloy sample/composition consists
essentially of the glassy alloy (with only a small incidental
amount of impurities). In another embodiment, the composition
includes a glassy alloy (with no observable trace of
impurities).
[0050] FIG. 2 shows a viscosity-temperature graph of an exemplary
glassy alloy, from an exemplary series of Zr--Ti--Ni--Cu--Be alloys
manufactured by Liquidmetal Technology. It should be noted that
there is no clear liquid/solid transformation for a bulk
solidifying amorphous metal during the formation of an amorphous
solid. The molten alloy becomes more and more viscous with
increasing undercooling until it approaches solid form around the
glass transition temperature. Accordingly, the temperature of
solidification front for bulk solidifying metallic glass-forming
alloys can be around glass transition temperature, where the alloy
will practically act as a solid for the purposes of pulling out the
quenched amorphous sheet product.
[0051] FIG. 3 shows the time-temperature-transformation (TTT)
cooling curve of an exemplary glassy alloy, or TTT diagram.
Bulk-solidifying amorphous metals do not experience a liquid/solid
crystallization transformation upon cooling, as with conventional
metals. Instead, the highly fluid, non-crystalline form of the
metal found at high temperatures (near a "melting temperature" Tm)
becomes more viscous as the temperature is reduced (near to the
glass transition temperature Tg), eventually taking on the outward
physical properties of a conventional solid.
[0052] Even though there is no liquid/crystallization
transformation for a bulk solidifying amorphous metal, a melting
temperature Tm may be defined as the thermodynamic liquidus
temperature of the corresponding crystalline phase. FIG. 3 shows
processing methods of die casting from at or above Tm to below Tg
without example time-temperature trajectory (1) hitting the TTT
curve. Time-temperature trajectories (2), (3), and (4) depict
processes at or below Tg being heated to temperatures below Tm.
Under this regime, the viscosity of bulk-solidifying amorphous
alloys at or above the melting temperature Tm could lie in the
range of about 0.1 poise to about 10,000 poise, and even sometimes
under 0.01 poise. A lower viscosity at the "melting temperature"
would provide faster and complete filling of intricate portions of
the shell/mold with a bulk solidifying amorphous metal for forming
the metallic glass parts. Furthermore, the cooling rate of the
molten metal to form a metallic glass part has to such that the
time-temperature profile during cooling does not traverse through
the nose-shaped region bounding the crystallized region in the TTT
diagram of FIG. 3. In FIG. 3, Tnose (at the peak of crystallization
region) is the critical crystallization temperature Tx where
crystallization is most rapid and occurs in the shortest time
scale.
[0053] The supercooled liquid region, the temperature region
between Tg and Tx is a manifestation of the stability against
crystallization of bulk solidification alloys. In this temperature
region the bulk solidifying alloy can exist as a high viscous
liquid. The viscosity of the bulk solidifying alloy in the
supercooled liquid region can vary between 1012 Pa s at the glass
transition temperature down to 105 Pa s at the crystallization
temperature, the high temperature limit of the supercooled liquid
region. Liquids with such viscosities can undergo substantial
plastic strain under an applied pressure. The embodiments herein
make use of the large plastic formability in the supercooled liquid
region as a forming and separating method.
[0054] Technically, the nose-shaped curve shown in the TTT diagram
describes Tx as a function of temperature and time. Thus,
regardless of the trajectory that one takes while heating or
cooling a metal alloy, when one hits the TTT curve, one has reached
Tx. In FIG. 3, Tx is shown as a dashed line as Tx can vary from
close to Tm to close to Tg.
[0055] The schematic TTT diagram of FIG. 3 shows processing methods
of die casting from at or above Tm to below Tg without the
time-temperature trajectory (shown as (1) as an example trajectory)
hitting the TTT curve. During die casting, the forming takes place
substantially simultaneously with fast cooling to avoid the
trajectory hitting the TTT curve. The processing methods for
superplastic forming (SPF) from at or below Tg to below Tm without
the time-temperature trajectory (shown as (2), (3) and (4) as
example trajectories) hitting the TTT curve. In SPF, the amorphous
bulk metallic glass is reheated into the supercooled liquid region
where the available processing window could be much larger than die
casting, resulting in better controllability of the process. The
SPF process does not require fast cooling to avoid crystallization
during cooling. Also, as shown by example trajectories (2), (3) and
(4), the SPF can be carried out with the highest temperature during
SPF being above Tnose or below Tnose, up to about Tm. If one heats
up a piece of metallic glass-forming alloy but manages to avoid
hitting the TTT curve, you have heated "between Tg and Tm," but one
would have not reached Tx.
[0056] Typical differential scanning calorimeter (DSC) heating
curves of bulk-solidifying metallic glass-forming alloys taken at a
heating rate of 20 C/min describe, for the most part, a particular
trajectory across the TTT data where one would likely see a Tg at a
certain temperature, a Tx when the DSC heating ramp crosses the TTT
crystallization onset, and eventually melting peaks when the same
trajectory crosses the temperature range for melting. If one heats
a bulk-solidifying metallic glass-forming alloy at a rapid heating
rate as shown by the ramp up portion of trajectories (2), (3) and
(4) in FIG. 4A, then one could avoid the TTT curve entirely, and
the DSC data would show a glass transition but no Tx upon heating.
Another way to think about it is trajectories (2), (3) and (4) can
fall anywhere in temperature between the nose of the TTT curve (and
even above it) and the Tg line, as long as it does not hit the
crystallization curve. That just means that the horizontal plateau
in trajectories might get much shorter as one increases the
processing temperature.
[0057] The methods herein can be valuable in the fabrication of
electronic devices using a glassy alloy. An electronic device
herein can refer to any electronic device known in the art. For
example, it can be a telephone, such as a cell phone, and a
land-line phone, or any communication device, such as a smart
phone, including, for example an iPhone.RTM., and an electronic
email sending/receiving device. It can be a part of a display, such
as a digital display, a TV monitor, an electronic-book reader, a
portable web-browser (e.g., iPad.RTM.), watch and a computer
monitor. It can also be an entertainment device, including a
portable DVD player, conventional DVD player, Blue-Ray disk player,
video game console, music player, such as a portable music player
(e.g., iPod.RTM.), etc. It can also be a part of a device that
provides control, such as controlling the streaming of images,
videos, sounds (e.g., Apple TV.RTM.), or it can be a remote control
for an electronic device. It can be a part of a computer or its
accessories, such as the hard drive tower housing or casing, laptop
housing, laptop keyboard, laptop track pad, desktop keyboard,
mouse, and speaker. The article can also be applied to a device
such as a watch or a clock.
[0058] Any ranges cited herein are inclusive. The terms
"substantially" and "about" used throughout this Specification are
used to describe and account for small fluctuations. For example,
they can refer to less than or equal to. .+-.5%, such as less than
or equal to .+-.2%, such as less than or equal to .+-.1%, such as
less than or equal to .+-.0.5%, such as less than or equal to
.+-.0.2%, such as less than or equal to .+-.0.1%, such as less than
or equal to .+-.0.05%.
[0059] The foregoing description, for purposes of explanation, used
specific nomenclature to provide a thorough understanding of the
described embodiments. However, it will be apparent to one skilled
in the art that the specific details are not required in order to
practice the described embodiments. Thus, the foregoing
descriptions of the specific embodiments described herein are
presented for purposes of illustration and description. They are
not target to be exhaustive or to limit the embodiments to the
precise forms disclosed. It will be apparent to one of ordinary
skill in the art that many modifications and variations are
possible in view of the above teachings.
EXAMPLES
[0060] The following non-limiting examples are provided to
illustrate aspects of the disclosure.
Example 1
[0061] In an example to demonstrate the improved thickness control
of the methods of the disclosure, comparative glassy alloys were
prepared. First, it was demonstrated that thermoplastic forming
alone does not provide for a reproducible and predictable thickness
with high tolerance. FIG. 4A depicts the result of four separate
attempts at forming a glassy alloy by thermoplastic forming to
within a tolerance window of 0.20+/-0.02 mm. Three of the four
samples were outside the tolerance range. FIG. 4B shows the
thickness of a thermoplastic pressed plate. The thickness was
non-uniform over the plate, measured to 0.28+/-0.09 mm (a variation
of approximately 30%).
[0062] Using the methods of the present disclosure, it was shown
that cold rolling allows for close control of the thickness of the
glassy alloy feedstock to thermoplastic forming processing. FIG. 4C
depicts cold rolled ribbon of glassy alloy. The cold rolled ribbon
has a thickness of 0.22+/-0.02 mm over the surface. As such, glassy
alloy parts that can be manufactured using the methods described
herein can have predictable and reproducible thickness within 10%
of the thickness value, or within 0.04 mm deviation of the part in
FIG. 4B.
Example 2
[0063] In accordance with aspects of the present disclosure, glassy
alloys that are formed by cold rolling followed by thermoplastic
forming according to methods of the present disclosure provide
structural relaxation that reduces or eliminates shear banding and
micro-cracking without loss of glassy alloy strength.
[0064] Table 1 shows the yield strength of a 4 mm wide.times.2 mm
thick Pt850 alloy when prepared as-cast and by cold rolling
followed by thermoplastic forming according to the disclosure. The
combination of cold-rolling and thermoplastic forming produced
glassy alloys having higher hardness with greater bending
deflection than the same as-cast glassy alloy. The yield strength
of the cold-rolled/thermoplastic glassy alloy was above what would
be expected by an as-cast system.
TABLE-US-00001 TABLE 1 Thermoplastic Deformation of Platinum Alloy
at 270.degree. C. As-cast Thermoplastic Sample .sigma..sub.m (MPa)
.delta..sub.f (mm) .sigma..sub.m (MPa) .delta..sub.f (mm) time 1
2558 1.82 2377 1.63 90 2 2580 1.89 2482 1.74 60 3 2555 1.83 2459
1.60 60 4 2554 1.48 2578 1.96 30 5 2515 1.70 2496 1.96 30 Mean 2552
.+-. 23 1.74 .+-. 0.16 2478 .+-. 72 1.78 .+-. 0.17
[0065] FIG. 5 shows the bending deflection curves of as-cast glassy
alloys compared to cold rolled/thermoplastic formed (TP) Pt850
alloys in a 3-points bending test to determine structural
relaxation embrittlement. Of note, there is no significant
degradation of fracture strain in TP samples at a thermoforming
time of 30 s, thereby demonstrating no structural relaxation
embrittlement of Pt-850 glassy alloy.
[0066] An example of punched Pt-850 glassy alloy part produce by a
cold-rolling/thermoplastic forming method of the disclosure is
shown in FIGS. 6A-C. FIG. 6A illustrates a cross-section of punched
Pt-850 glassy alloy produced according to the methods of the
disclosure, showing a smooth, flat shear fracture near the top
surface, and a rough shear fracture near the bottom surface.
Exploded views show that there is nearly no undercut (FIG. 6B) or
burr (FIG. 6C) formed during punching.
[0067] As demonstrated, the structural properties of the glassy
alloys produced according to the methods of the disclosure provide
material that is excellent for shaping via machine processes such
as punching. For instance, given the reproducibility of thickness
and lack of structural relaxation embrittlement described herein,
the glassy alloy materials produced according to the methods of the
disclosure are particularly suited for shaping via machine
processes such as punching.
[0068] While this disclosure has been described with reference to
specific embodiments, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof, without departing from the spirit
and scope of the disclosure. In addition, modifications may be made
to adapt the teachings of the disclosure to particular situations
and materials, without departing from the essential scope thereof.
Thus, the disclosure is not limited to the particular examples that
are disclosed herein, but encompasses all embodiments falling
within the scope of the appended claims.
* * * * *