U.S. patent application number 14/161434 was filed with the patent office on 2014-07-24 for melt overheating method for improved toughness and glass-forming ability of metallic glasses.
This patent application is currently assigned to GLASSIMETAL TECHNOLOGY, INC.. The applicant listed for this patent is GLASSIMETAL TECHNOLOGY, INC.. Invention is credited to Marios D. DEMETRIOU, Michael FLOYD, Glenn GARRETT, William L. JOHNSON, David S. LEE, Jong Hyun NA.
Application Number | 20140202596 14/161434 |
Document ID | / |
Family ID | 50114540 |
Filed Date | 2014-07-24 |
United States Patent
Application |
20140202596 |
Kind Code |
A1 |
NA; Jong Hyun ; et
al. |
July 24, 2014 |
MELT OVERHEATING METHOD FOR IMPROVED TOUGHNESS AND GLASS-FORMING
ABILITY OF METALLIC GLASSES
Abstract
A method of forming a bulk metallic glass is provided. The
method includes overheating the alloy melt to a temperature above a
threshold temperature, T.sub.tough, associated with the metallic
glass demonstrating substantial improvement in toughness compared
to the toughness demonstrated in the absence of overheating the
melt above T.sub.liquidus, and another threshold temperature,
T.sub.GFA, associated with the metallic glass demonstrating
substantial improvement in glass-forming ability compared to the
glass-forming ability demonstrated in the absence of overheating
the melt above T.sub.liquidus. After overheating the alloy melt to
above T.sub.tough and T.sub.GFA, the melt may be cooled and
equilibrated to an intermediate temperature below both T.sub.tough
and T.sub.GFA but above T.sub.liquidus, and subsequently quenched
at a high enough rate to form a bulk metallic glass.
Inventors: |
NA; Jong Hyun; (Pasadena,
CA) ; FLOYD; Michael; (Pasadena, CA) ; LEE;
David S.; (Wenham, MA) ; DEMETRIOU; Marios D.;
(West Hollywood, CA) ; JOHNSON; William L.; (San
Marino, CA) ; GARRETT; Glenn; (Pasadena, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GLASSIMETAL TECHNOLOGY, INC. |
PASADENA |
CA |
US |
|
|
Assignee: |
GLASSIMETAL TECHNOLOGY,
INC.
PASADENA
CA
|
Family ID: |
50114540 |
Appl. No.: |
14/161434 |
Filed: |
January 22, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61755177 |
Jan 22, 2013 |
|
|
|
Current U.S.
Class: |
148/538 ;
148/540; 148/549; 148/553; 148/555 |
Current CPC
Class: |
C22C 45/003 20130101;
C22C 45/02 20130101; B22D 46/00 20130101; C22C 45/001 20130101;
C22C 45/04 20130101; C22C 45/005 20130101; C22C 33/003 20130101;
B22D 27/04 20130101; C22C 45/00 20130101; C22C 45/08 20130101; C22C
45/10 20130101; C22C 1/002 20130101 |
Class at
Publication: |
148/538 ;
148/549; 148/540; 148/555; 148/553 |
International
Class: |
C22F 1/00 20060101
C22F001/00; C22C 45/00 20060101 C22C045/00; C22C 45/04 20060101
C22C045/04; C22C 45/08 20060101 C22C045/08; C22C 45/02 20060101
C22C045/02 |
Claims
1. A method of forming a bulk metallic glass, comprising: melting
an alloy by heating the alloy to a temperature above the liquidus
temperature, T.sub.liquidus; overheating the alloy melt to an
overheating temperature above a threshold temperature, T.sub.tough,
associated with the metallic glass demonstrating increased
toughness compared to the toughness demonstrated by heating the
melt just above T.sub.liquidus and quenching the melt to form a
bulk metallic glass.
2. The method of claim 1, wherein the temperature of the overheated
alloy melt is also above a threshold temperature, T.sub.GFA,
associated with the metallic glass demonstrating increased critical
rod diameter compared to the critical rod diameter demonstrated by
heating the melt just above T.sub.liquidus.
3. The method of claim 2, wherein T.sub.tough is greater than
T.sub.GFA.
4. The method of claim 1, wherein the toughness of the metallic
glass is at least 25% greater than the toughness of the metallic
glass formed in the absence of overheating above
T.sub.liquidus.
5. The method of claim 1, wherein the toughness of the metallic
glass is at least 50% greater than the toughness of the metallic
glass formed in the absence of overheating above
T.sub.liquidus.
6. The method of claim 2, wherein the critical rod diameter is at
least 25% greater than the critical rod diameter attained in the
absence of overheating above T.sub.liquidus.
7. The method of claim 2, wherein the critical rod diameter is at
least 50% greater than the critical rod diameter attained in the
absence of overheating above T.sub.liquidus.
8. The method of claim 1, further comprising cooling the alloy melt
to an intermediate temperature below T.sub.tough and T.sub.GFA but
above T.sub.liquidus, equilibrating the alloy melt at the
intermediate temperature, and quenching the alloy melt to form the
metallic glass.
9. The method of claim 1, wherein the alloy is selected from a
Zr-based alloy, Ti-based alloy, Al-based alloy, Mg-based alloy,
Ce-based alloy, La-based alloy, Y-based alloy, Fe-based alloy,
Ni-based alloy, Co-based alloy, Cu-based alloy, Au-based alloy,
Pd-based alloy, and Pt-based alloy.
10. The method of claim 1, wherein the alloy is represented by the
formula X.sub.100-a-bY.sub.aZ.sub.b where: X is Ni, Fe, Co, Pd, Pt,
Au, Cu or combinations thereof; Y is Cr, Mo, Mn, Nb, Ta, Ni, Cu,
Co, Fe, Pd, Pt, Ag or combinations thereof; Z is P, B, Si, Ge, C or
combinations thereof; a is between 2 and 45 at %; and b is between
15 and 25 at %.
11. The method of claim 1, wherein the alloy is represented by the
formula X.sub.100-a-bY.sub.aZ.sub.b, wherein: X is Ni, Fe, Co or
combinations thereof, Y is Cr, Mo, Mn, Nb, Ta or combinations
thereof, Z is P, B, Si, Ge or combinations thereof, a is between 5
and 15 at %, and b is between 15 and 25 at %.
12. The method of claim 1, wherein the alloy melt is heated by a
process selected from inductive heating, resistively heating (in a
furnace), a plasma arc heating, and joule heating.
13. The method of claim 1, wherein the melt is held in a crucible
comprising a material selected from fused or crystalline silica, a
ceramic, alumina, zirconia, graphite, and a water-cooled hearth
made of copper or silver.
14. A method of forming a shaped metallic glass article,
comprising: melting a metallic glass forming alloy by heating the
alloy to a temperature above the liquidus temperature of the alloy,
T.sub.liquidus. overheating the alloy melt to an overheating
temperature above both a threshold temperature, T.sub.tough,
associated with the metallic glass demonstrating increased
toughness compared to the toughness demonstrated by heating the
melt just above T.sub.liquidus, and a threshold temperature,
T.sub.GFA, associated with the alloy demonstrating an increase in
critical rod diameter compared to the critical rod diameter
demonstrated by heating the melt just above T.sub.liquidus; and
quenching the alloy melt to form the alloy melt into a shaped
metallic glass article.
15. The method of claim 14, further comprising cooling and
equilibrating the alloy melt to an intermediate temperature below
T.sub.tough and T.sub.GFA but above T.sub.liquidus; and quenching
the alloy melt to form a shaped metallic glass article.
16. The method of claim 14, wherein the toughness of the metallic
glass is at least 25% greater than the toughness of the metallic
glass formed in the absence of overheating above
T.sub.liquidus.
17. The method of claim 14, wherein the toughness of the metallic
glass is at least 50% greater than the toughness of the metallic
glass formed in the absence of overheating above
T.sub.liquidus.
18. The method of claim 14, wherein the critical rod diameter is at
least 25% greater than the critical rod diameter attained in the
absence of overheating above T.sub.liquidus.
19. The method of claim 14, wherein the critical rod diameter is at
least 50% greater than the critical rod diameter attained in the
absence of overheating above T.sub.liquidus.
20. The method of claim 14, wherein the alloy comprises a material
selected from a group consisting of a Zr-based alloy, Ti-based
alloy, Al-based alloy, Mg-based alloy, Ce-based alloy, La-based
alloy, Y-based alloy, Fe-based alloy, Ni-based alloy, Co-based
alloy, Cu-based alloy, Au-based alloy, Pd-based alloy, and Pt-based
alloy.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Patent Application No. 61/755,177, entitled "Melt
Overheating Method For Improved Toughness and Glass-Forming Ability
of Metallic Glasses" filed on Jan. 22, 2013, which is incorporated
herein by reference in its entirety.
FIELD
[0002] The present disclosure is directed to a method of
overheating the melt of an alloy capable of forming metallic glass
prior to quenching the melt in order to improve the glass-forming
ability of the alloy and/or the toughness of the metallic
glass.
BACKGROUND
[0003] Overheating the melt of alloys capable of forming metallic
glass to temperatures sufficiently higher than the melting
temperature is shown to influence certain kinetic properties of the
liquid. Specifically, Lin et al. (U.S. Pat. No. 5,797,443)
demonstrated that by overheating the melt of a bulk-solidifying
Zr-based amorphous metal above a threshold temperature, which is
sufficiently higher than the melting temperature, the degree to
which the alloy can be undercooled to below the melting temperature
by quenching increases. Lin et al. conjectured that by overheating
the melt, certain oxide inclusions were dissolved into the melt and
therefore could not serve as sites for heterogeneous nucleation of
crystalline phases. The implication of a larger degree of
undercooling is that the glass-forming ability of the alloy is
enhanced. As such, the critical cooling rate (i.e. lowest cooling
rate required to bypass crystallization of the alloy and form the
amorphous phase) is decreased, while the critical casting thickness
(i.e. largest lateral dimension of parts that can be formed with an
amorphous phase) is increased. Lin et al. did not directly
demonstrate that the critical casting thickness of the alloy
increases with melt overheating, but concluded so by interpreting
the undercooling results in the context of crystallization
kinetics.
[0004] Lin et al. also discloses that after processing the melt at
a temperature higher than T.sub.GFA, it is possible to cool and
isothermally hold to an intermediate temperature between T.sub.GFA
and T.sub.liquidus prior to quenching without substantially losing
the gains in glass-forming ability attained by initially
overheating to above T.sub.GFA. In other words, once the melt is
heated to a temperature higher than T.sub.GFA, its capacity undergo
deeper undercooling is maintained even if it is subsequently
annealed at temperatures between T.sub.GFA and T.sub.liquidus prior
to undercooling.
[0005] However, Lin et al. did not demonstrate, suggest, or imply
that overheating the melt above some threshold temperature would
have any influence on the mechanical properties of the amorphous
metal, such as the fracture toughness.
BRIEF SUMMARY
[0006] The present disclosure provides methods of forming bulk
metallic glasses or shaped metallic glass articles having higher
toughness by overheating the alloy melt.
[0007] The disclosure is directed to a method of processing alloys
into metallic glasses or metallic glass articles. The method
includes melting an alloy by heating to a temperature above the
liquidus temperature of the alloy, T.sub.liquidus. The method also
includes overheating the alloy melt to a temperature above a
threshold temperature, T.sub.tough, associated with the metallic
glass (i.e. the alloy in an amorphous phase) demonstrating
increased toughness compared to the toughness demonstrated by
heating the alloy melt just above T.sub.liquidus. The method
further includes quenching the alloy melt at a high enough rate to
form metallic glasses or shaped metallic glass articles.
[0008] In another embodiment, the temperature of the overheated
alloy melt is also above another threshold temperature, T.sub.GFA,
associated with the alloy demonstrating increased glass-forming
ability compared to the glass-forming ability demonstrated by
heating the alloy melt just above T.sub.liquidus.
[0009] In yet another embodiment, T.sub.tough is greater than
T.sub.GFA.
[0010] In yet another embodiment, both T.sub.tough and T.sub.GFA
are greater than T.sub.liquidus.
[0011] In yet another embodiment, the method also includes cooling
the alloy melt following overheating to above T.sub.tough and
T.sub.GFA to an intermediate temperature below T.sub.tough and
T.sub.GFA but above T.sub.liquidus and equilibrating the alloy melt
at the intermediate temperature, and subsequently quenching the
alloy melt at a high enough rate to form a metallic glass
article.
[0012] In yet another embodiment, a method of forming a shaped
metallic glass article is provided. The method includes melting a
metallic glass forming alloy by heating the alloy to a temperature
above the liquidus temperature of the alloy, T.sub.liquidus. The
method also includes overheating the alloy melt to a temperature
above both a threshold temperature, T.sub.tough, associated with
the metallic glass demonstrating substantial improvement in
toughness compared to the toughness demonstrated by heating the
melt just above T.sub.liquidus, and another threshold temperature,
T.sub.GFA, associated with the alloy demonstrating substantial
improvement in glass-forming ability compared to the glass-forming
ability demonstrated by heating the melt just above T.sub.liquidus.
The method further includes simultaneously or subsequently
quenching the alloy melt at a high enough rate to form a shaped
metallic glass article.
[0013] In yet another embodiment, following overheating to above
T.sub.tough and T.sub.GFA, the method of forming a shaped metallic
glass article includes cooling and equilibrating the alloy melt to
an intermediate temperature below T.sub.tough and T.sub.GFA but
above T.sub.liquidus. The method further includes simultaneously or
subsequently quenching the alloy melt at a high enough rate to form
a shaped metallic glass article.
[0014] In yet another embodiment, the metallic glass article having
a lateral dimension of at least 0.5 mm made according to the
present method is capable of undergoing macroscopic plastic
deformation without fracturing catastrophically under a bending
load.
[0015] In yet another embodiment, the alloy or metallic glass is
Zr-based, Ti-based, Al-based, Mg-based, Ce-based, La-based,
Y-based, Fe-based, Ni-based, Co-based, Cu-based, Au-based,
Pd-based, or Pt-based.
[0016] In yet another embodiment, the alloy or metallic glass is
represented by the following formula:
X.sub.100-a-bY.sub.aZ.sub.b Eq. (1)
[0017] wherein:
[0018] X is Ni, Fe, Co, Pd, Pt, Au, Cu or combinations thereof;
[0019] Y is Cr, Mo, Mn, Nb, Ta, Ni, Cu, Co, Fe, Pd, Pt, Ag or
combinations thereof;
[0020] Z is P, B, Si, Ge, C or combinations thereof;
[0021] a is between 2 and 45 at %; and
[0022] b is between 15 and 25 at %.
[0023] In yet another embodiment, the alloy or metallic glass is
represented by the following formula:
X.sub.100-a-bY.sub.aZ.sub.b, Eq. (2)
where:
[0024] X is Ni, Fe, Co or combinations thereof
[0025] Y is Cr, Mo, Mn, Nb, Ta or combinations thereof
[0026] Z is P, B, Si, Ge or combinations thereof
[0027] a is between 5 and 15 at %
[0028] b is between 15 and 25 at %.
[0029] In yet another embodiment, the alloy melt is heated by a
process that may include inductive heating, resistively heating (in
a furnace), a plasma arc heating, or joule heating, where the melt
is held in a crucible made of fused or crystalline silica, a
ceramic such as alumina or zirconia, graphite, or a water-cooled
hearth made of copper or silver.
[0030] In yet another embodiment, the alloy melt is quenched by a
process that may include quenching the crucible containing the melt
in a bath of room temperature water, iced water, or oil. The
crucible is made of any of the aforementioned materials.
Alternatively, the method includes quenching the melt by driving
the melt under pressure or pouring the melt into a metal mold. In
some embodiments, the mold is made of copper, brass, or steel.
[0031] 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 examination of the specification or may be
learned by the practice of the disclosed subject matter. A further
understanding of the nature and advantages of the present
disclosure may 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 DRAWINGS
[0032] The description will be more fully understood with reference
to the following figures and data graphs, which are presented as
various embodiments of the disclosure and should not be construed
as a complete recitation of the scope of the disclosure,
wherein:
[0033] FIG. 1 provides a schematic process profile to achieve
improved glass-forming ability and toughness in alloys and metallic
glasses in accordance with embodiments of the present
disclosure.
[0034] FIG. 2 provides a plot showing the effect of melt
overheating on the critical rod diameter and notch toughness of
alloy and metallic glass
Ni.sub.69Cr.sub.8.5Nb.sub.3P.sub.16.5B.sub.3 in accordance with
embodiments of the present disclosure.
[0035] FIG. 3 provides a plot showing the effect of melt
overheating on the critical rod diameter and notch toughness of
alloy and metallic glass
Ni.sub.72.5Cr.sub.5Nb.sub.3P.sub.16.5B.sub.3 in accordance with
embodiments of the present disclosure.
[0036] FIG. 4 provides a plot showing the effect of melt
overheating on the critical rod diameter and notch toughness of
alloy and metallic glass
Ni.sub.68.6Cr.sub.8.7Nb.sub.3P.sub.16B.sub.3.2Si.sub.0.5 in
accordance with embodiments of the present disclosure.
[0037] FIG. 5 provides a plot showing the effect of melt
overheating on the critical rod diameter and notch toughness of
alloy and metallic glass
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3 in accordance
with embodiments of the present disclosure.
[0038] FIG. 6 provides a plot showing the effect of melt
overheating on the critical rod diameter and notch toughness of
alloy and metallic glass
Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5 in
accordance with embodiments of the present disclosure.
[0039] FIG. 7 provides a plot showing the effect of cooling to an
intermediate temperature after overheating the melt and prior to
quenching on the critical rod diameter and notch toughness of alloy
and metallic glass
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3 in accordance
with embodiments of the present disclosure.
[0040] FIG. 8 provides a plot showing the effect of time spent at
an intermediate temperature after overheating the melt and prior to
quenching on the critical rod diameter and notch toughness of alloy
and metallic glass
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3 in accordance
with embodiments of the present disclosure.
DETAILED DESCRIPTION
[0041] The present disclosure may be understood by reference to the
following detailed description, taken in conjunction with the
drawings as described below. It is noted that, for purposes of
illustrative clarity, certain elements in various drawings may not
be drawn to scale.
Description of the Processing Methods
[0042] The present disclosure provides methods of forming bulk
metallic glasses or shaped metallic glass articles of improved
toughness and glass forming ability by overheating the alloy melt
to a temperature higher than T.sub.tough and T.sub.GFA, which are
both above T.sub.liquidus, prior to quenching. The present
disclosure also provides an alternative method, whereas after
overheating the alloy melt to above T.sub.tough and T.sub.GFA, the
melt is cooled and equilibrated to an intermediate temperature
below both T.sub.tough and T.sub.GFA but above T.sub.liquidus, and
subsequently quenched at a high enough rate to form a bulk metallic
glass.
[0043] In the context of the present disclosure, glass-forming
ability is understood as measured by the "critical rod diameter" as
defined herein. Where the disclosure refers to improved or
increased glass-forming ability, it will be understood to be as
measured by the "critical rod diameter." In the context of the
present disclosure, toughness is measured by "notch toughness" as
defined herein. Where the disclosure refers to improved or
increased toughness, it will be understood to be as measured by the
"notch toughness."
[0044] In support of the former method, the present disclosure
demonstrates that once the melt is heated to a temperature higher
than T.sub.GFA, the glass forming ability of the alloy is
considerably higher as compared to heating the melt just above
T.sub.liquidus. The disclosure further demonstrates that once the
melt is heated to a temperature higher than T.sub.tough, the
toughness of the metallic glass is considerably higher as compared
to heating the melt just above T.sub.liquidus.
[0045] In some embodiments, "heating the melt just above
T.sub.liquidus" or "in the absence of overheating" is intended to
imply that the melt is overheated by less than 50.degree. C. above
the alloy liquidus temperature. In other embodiments, "just above
T.sub.liquidus" or "in the absence of overheating" is intended to
imply that the melt is overheated by less than 5% of the alloy
liquidus temperature (where T.sub.liquidus is expressed in units of
Kelvin).
[0046] In support of the latter method, the present disclosure
demonstrates that once the melt is heated to a temperature higher
than T.sub.GFA and then annealed below T.sub.GFA prior to quenching
to form a glass, its higher glass-forming ability is actually
retained. More surprisingly, the present disclosure reveals that
once the melt is heated to a temperature higher than T.sub.tough
and then annealed at an intermediate temperature below T.sub.tough
prior to quenching to form a glass, its higher toughness is also
retained.
[0047] The behavior of amorphous metals that are processed in the
high-temperature melt state is complex. Quite unexpectedly, an
independent threshold temperature above the liquidus temperature
T.sub.liquidus is identified to be associated with enhanced
toughness, and is referred to as a first threshold temperature
L.sub.tough hereafter. Specifically, the metallic glasses processed
by overheating the alloy melt above this threshold temperature,
T.sub.tough, have an improved toughness at room temperature over
the metallic glasses processed by heating the alloy melt above
T.sub.liquidus but below T.sub.tough.
[0048] Specifically, T.sub.tough is defined as the melt overheating
temperature associated with a substantial improvement in toughness,
as measured by notch toughness, of the metallic glass at room
temperature as compared to the toughness demonstrated in the
absence of overheating above T.sub.liquidus, More specifically,
T.sub.tough may be identified as the temperature following the
steepest increase in toughness with increasing melt overheating
temperature (i.e. the temperature following the largest slope of
the toughness function against temperature above
T.sub.liquidus).
[0049] Another threshold temperature, T.sub.GFA, is defined as the
melt overheating temperature associated with substantial
improvement in glass-forming ability, as measured by critical rod
diameter, as compared to the glass-forming ability demonstrated in
the absence of overheating above T.sub.liquidus. More specifically,
T.sub.GFA may be identified as the temperature following the
steepest increase in glass forming ability with increasing melt
overheating temperature (i.e. the temperature following the largest
slope of the glass forming ability function against temperature
above T.sub.liquidus).
[0050] In some embodiments, "significant improvement" in toughness
and glass-forming ability may be interpreted as an improvement of
at least 10% compared to the respective values obtained in the
absence of overheating above T.sub.liquidus. In some embodiments,
"substantial improvement" in toughness and glass-forming ability
may be interpreted as an improvement of at least 25% compared to
the respective values obtained in the absence of overheating above
T.sub.liquidus. In some embodiments, "substantial improvement" is
interpreted as an improvement of at least 50% compared to the
respective values obtained in the absence of overheating above
T.sub.liquidus. In some embodiments, "substantial improvement" is
interpreted as an improvement of at least 75% compared to the
respective values obtained in the absence of overheating above
T.sub.liquidus.
[0051] In some embodiments, "substantial improvement" in toughness
and glass-forming ability may be interpreted as an improvement of
at least 50% compared to the respective values obtained in the
absence of overheating above T.sub.liquidus attained by overheating
the melt by at least 100.degree. C. above T.sub.liquidus. In some
embodiments, "substantial improvement" is interpreted as an
improvement of at least 50% compared to the respective values
obtained in the absence of overheating above T.sub.liquidus
attained by overheating the melt by at least 50.degree. C. above
T.sub.liquidus. In some embodiments, "substantial improvement" is
interpreted as an improvement of at least 50% compared to the
respective values obtained in the absence of overheating above
T.sub.liquidus attained by overheating the melt by at least
25.degree. C. above T.sub.liquidus.
[0052] FIG. 1 provides a schematic process profile to achieve
improved glass-forming ability and toughness in alloys and metallic
glasses in accordance with embodiments of the present disclosure.
As shown in FIG. 1, one processing path 102 includes passing
through the identified threshold temperatures associated with
improved toughness, T.sub.tough, and with improved glass-forming
ability, T.sub.GFA, followed by quenching from an overheating
temperature above T.sub.tough, like for example from the designated
temperature T.sub.H.
[0053] Both T.sub.tough and T.sub.GFA may be higher than the
solidus and liquidus temperatures T.sub.solidus and T.sub.liquidus,
respectively. In some embodiments, T.sub.tough may be higher than
T.sub.GFA, as shown in FIG. 1. Although this temperature order is
not limiting, most metallic glass systems may have T.sub.tough
higher than T.sub.GFA. In other embodiments, T.sub.tough may be
lower than T.sub.GFA.
[0054] Regardless of the order of T.sub.tough versus T.sub.GFA, it
is observed that T.sub.tough is independent of and different from
T.sub.GFA. Accordingly, attempts to achieve high glass-forming
ability by overheating the melt above a certain T.sub.GFA would not
necessarily lead to a tougher metallic glass.
[0055] As shown in FIG. 1, in order to achieve high glass-forming
ability, the melt can be heated to a temperature higher than
T.sub.GFA prior to quenching. Furthermore, the melt can be heated
to a temperature higher than both T.sub.GFA and T.sub.tough prior
to quenching in order to achieve both a high glass-forming ability
and a high toughness.
[0056] An alloy would not only have improved glass-forming ability,
i.e. being capable of forming a metallic glass in larger lateral
dimensions, but would also form a metallic glass article or
hardware having an improved toughness according to the present
overheating method. One of the benefits of the improved toughness
is to enable the metallic glass article or hardware formed from the
alloy to evade catastrophic fracture upon loading initiating from
structural flaws, particularly in bending loading. Specifically, an
amorphous metal article having a lateral dimension of at least 0.5
mm made according to the present method would be able to undergo
macroscopic plastic bending when overloaded, evading catastrophic
fracture. This improved toughness, together with the improved
glass-forming ability, can result in an improved overall
engineering applicability and performance.
[0057] The present disclosure also provides a method for the melt
to retain "memory" of its high temperature state at intermediate
temperatures. Specifically, after heating the melt to a temperature
higher than both T.sub.GFA and T.sub.tough, the melt may be cooled
to an intermediate temperature below T.sub.GFA and T.sub.tough but
above T.sub.liquidus prior to quenching, and may be held
isothermally at the intermediate temperature without substantially
losing the gains in both the glass-forming ability and toughness
attained by initially overheating to above T.sub.GFA and
T.sub.tough. FIG. 1 illustrates an alternative path 104 involving
the isothermal step at an intermediate temperature which is lower
than both T.sub.GFA and T.sub.tough but higher than T.sub.liquidus,
like for example at the designated temperature T.sub.L
[0058] One of the benefits of the alternative path is to limit the
degradation of a metal mold tool by avoiding injecting the melt
into the mold tool from very high temperatures. For processes that
utilize pressure to drive the processed melt into a metal mold in
order to shape the melt and simultaneously quench the melt to form
an amorphous metal article or hardware, such as die casting, the
ability of the melt to retain "memory" of its high temperature
state is very important. This is because the tool life of the mold
depends strongly on the temperature of the alloy melt. To achieve
the high toughness and high glass-forming ability, the alloy is
overheated to be above T.sub.GFA and T.sub.tough which may be much
higher than T.sub.liquidus. With such high temperatures, the tool
life of mold may be dramatically shortened using the present method
at a temperature above T.sub.GFA and T.sub.tough, like for example
at T.sub.H, as shown in processing path 102. However, injecting the
melt into the mold at a lower intermediate temperature below
T.sub.GFA and T.sub.rough but above T.sub.liquidus, like for
example at T.sub.L, according to the alternative processing path
104, would diminish any adverse effects on the tool life. Other
potential benefits include lower power requirements for heating the
melt, less thermal shrinkage of the part, and potentially better
melt flow control with higher viscosity at lower temperature.
[0059] The present method is applicable to any processing that
produces an amorphous metal article or part by melting and
quenching a metallic alloy.
[0060] The method is also applicable, without limitation, to any
heating process that involve melting the alloy. Heating processes
may include, without limitation, inductive heating, resistive
heating (e.g. in a furnace), plasma arc heating, or joule heating,
where the alloy melt is held in a crucible. The crucible material
may include, without limitation, fused or crystalline silica, a
ceramic such as alumina or zirconia, graphite, or a water-cooled
hearth made of copper or silver.
[0061] The method is also applicable, without limitation, to any
quenching processes that involve quenching the crucible containing
the melt in a bath of room temperature water, iced water, or oil,
or quenching the melt by driving it under pressure or pouring it
into a metal mold made of copper, brass, or steel. The crucible may
be made of any of the aforementioned materials.
[0062] The disclosed methods are applicable to all metal alloys
capable of forming a metallic glass by quenching the alloy melt
form high temperature. A "critical cooling rate", which is defined
as the cooling rate required to avoid crystallization and form the
amorphous phase of the alloy (i.e. the metallic glass) determines
the critical rod diameter. The lower the critical cooling rate of
an alloy, the larger its critical rod diameter. The critical
cooling rate R.sub.c in K/s and critical rod diameter d.sub.c in mm
are related via the following approximate empirical formula:
R.sub.c=1000/d.sub.c.sup.2 Eq. (2)
[0063] According to Eq. (2), the critical cooling rate for an alloy
having a critical rod diameter of about 1 mm, as in the case of the
alloys according to embodiments of the present disclosure, is only
about 10.sup.3 K/s.
[0064] Generally, three categories are known in the art for
identifying the ability of a metal alloy to form glass (i.e. to
bypass the stable crystal phase and form an amorphous phase). Metal
alloys having critical cooling rates in excess of 10.sup.12 K/s are
typically referred to as non-glass formers, as it is physically
impossible to achieve such cooling rates over a meaningful
thickness. Metal alloys having critical cooling rates in the range
of 10.sup.5 to 10.sup.12 K/s are typically referred to as marginal
glass formers, as they are able to form glass over thicknesses
ranging from 1 to 100 micrometers according to Eq. (2). Metal
alloys having critical cooling rates on the order of 10.sup.3 or
less, and as low as 1 or 0.1 K/s, are typically referred to as bulk
glass formers, as they are able to form glass over thicknesses
ranging from 1 millimeter to several centimeters. The glass-forming
ability of a metallic alloy is, to a very large extent, dependent
on the combination and composition of the alloy. It is important to
state that the combinational and compositional ranges for alloys
capable of forming marginal glass formers are considerably broader
than those for forming bulk glass formers.
[0065] The present method is applicable to any metallic
glass-forming alloy, including but not limited to, Zr-based,
Ti-based, Al-based, Mg-based, Ce-based, La-based, Ca-based,
Y-based, Fe-based, Ni-based, Co-based, Cu-based, Au-based,
Pd-based, and Pt-based.
[0066] Without limitation, Zr-based glass-forming alloys may
include elements selected from the group consisting of Ti, Ni, Cu,
Be, Hf, Nb, V, Al, Sn, Ag, Pd, Fe, Co, and Cr.
[0067] Without limitation, Fe-based glass-forming alloys may
include elements selected from the group consisting of Co, Ni, Mo,
Cr, P, C, B, Si, Al, Zr, W, Mn, Y, and Er.
[0068] Without limitation, Ni-based glass-forming alloys may
include elements selected from the group consisting of Co, Fe, Cu,
Mo, Cr, P, B, Si, Sn, Nb, Ta, V, and Mn.
[0069] Without limitation, Cu-based glass-forming alloys may
include elements selected from the group consisting of Zr, Ti, Ni,
Au, Ag, Hf, Nb, V, Si, Sn, and P.
[0070] Without limitation, Au-based glass-forming alloys may
include elements selected from the group consisting of Cu, Si, Ag,
Pd, Pt, Ge, Y, and Al.
[0071] Without limitation, Pd-based glass-forming alloys may
include elements selected from the group consisting of Pt, Ni, Cu,
P, Si, Ge, Ag, Au, Fe, and Co.
[0072] Without limitation, Pt-based glass-forming alloys may
include elements selected from the group consisting of Pd, Ni, Cu,
P, Si, Ge, Ag, Au, Fe, and Co.
[0073] In some embodiments, for certain alloys whose melt can be
fluxed to increase glass-forming ability, fluxing can also help
achieve both high toughness and high glass-forming ability without
the need for melt overheating. A fluxing method is disclosed in a
recent patent application U.S. Patent No. 61/913,732, filed on Dec.
9, 2013, entitled "Melt fluxing method for improved toughness and
glass-forming ability of metallic glasses and glass forming
alloys", which is incorporated herein by reference in its entirety.
Fluxing the alloy melt may help avoid overheating to very high
temperatures in order to achieve high toughness and high
glass-forming ability.
EXAMPLES
[0074] The following non-limiting examples are illustrative of
aspects of the present disclosure.
Example 1
Melt Overheating to a Temperature Above T.sub.tough and
T.sub.GFA
[0075] To demonstrate the effects of the method of melt overheating
at T.sub.H on glass-forming ability (GFA) and toughness, Ni-based
glass-forming alloys from the Ni--Cr--Nb--P--B family, disclosed in
a recent application (U.S. Patent Application No. 61/720,015,
entitled "Bulk Nickel-Based Chromium and Phosphorous Bearing
Metallic Glasses with High Toughness", filed on Oct. 30, 2012,
which is incorporated herein by reference), and the Fe-based glass
forming alloy
Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5 are
used here as example systems.
[0076] The glass-forming ability of each alloy was assessed by
determining the "critical" rod diameter", defined as the maximum
rod diameter at which the amorphous phase can be formed when
processed by the method of water quenching the molten alloy in
quartz tubes having 0.5 mm wall thickness.
[0077] FIG. 2 provides a plot showing the effect of melt
overheating on the glass-forming ability and toughness of alloy and
metallic glass Ni.sub.69Cr.sub.8.5Nb.sub.3P.sub.16.5B.sub.3 in
accordance with embodiments of the present disclosure. As presented
in FIG. 2, the glass-forming ability is shown to improve if the
melt is heated to above its T.sub.GFA of 1100.degree. C. or higher.
For example, when the melt is heated to 1050.degree. C., which is
below T.sub.GFA, and subsequently quenched, the alloy is found to
have a critical rod diameter of about 3 mm. In contrast, when the
melt is heated to 1250.degree. C., which is substantially higher
than T.sub.GFA, and subsequently quenched, the alloy yields a
substantially improved glass-forming ability, i.e. a critical rod
diameter of 10 mm.
[0078] However, the alloy with improved glass-forming ability still
lacks good toughness when heated to 1250.degree. C., showing a
room-temperature notch toughness of just 30 MPa m.sup.1/2.
Surprisingly, when heating the alloy to 1350.degree. C., which is
above its T.sub.tough of 1300.degree. C., and subsequently
quenching, the alloy forms a metallic glass that has a
substantially improved toughness of about 80 MPa m.sup.1/2.
[0079] The same effect is shown for four more alloys. For each
alloy, one can define values for T.sub.GFA and T.sub.tough. FIG. 3
provides a plot showing the effect of melt overheating on the
glass-forming ability and toughness of alloy and metallic glass
Ni.sub.72.5Cr.sub.5Nb.sub.3P.sub.16.5B.sub.3 in accordance with
embodiments of the present disclosure. As shown in FIG. 3, alloy
Ni.sub.72.5Cr.sub.5Nb.sub.3P.sub.16.5B.sub.3 has a T.sub.GFA of
1100.degree. C. and T.sub.tough of 1150.degree. C.
[0080] FIG. 4 provides a plot showing the effect of melt
overheating on the glass-forming ability and toughness of alloy and
metallic glass
Ni.sub.68.6Cr.sub.8.7Nb.sub.3P.sub.16B.sub.3.2Si.sub.0.5 in
accordance with embodiments of the present disclosure. As shown in
FIG. 4, the
Ni.sub.68.6Cr.sub.8.7Nb.sub.3P.sub.16B.sub.3.2Si.sub.0.5 alloy has
a T.sub.GFA of 1150.degree. C. and T.sub.tough of 1250.degree.
C.
[0081] FIG. 5 provides a plot showing the effect of melt
overheating on the glass-forming ability and toughness of alloy and
metallic glass Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3
in accordance with embodiments of the present disclosure. As shown
in FIG. 5, the Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.3.46B.sub.3
alloy has a T.sub.GFA of 1125.degree. C. and T.sub.tough of
1250.degree. C.
[0082] FIG. 6 provides a plot showing the effect of melt
overheating on the glass-forming ability and toughness of alloy and
metallic glass
Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5 in
accordance with embodiments of the present disclosure. As shown in
FIG. 6, the
Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5
alloy has a T.sub.GFA of 1350.degree. C. and T.sub.tough of
1450.degree. C.
[0083] The alloy and metallic glass compositions along with the
associated T.sub.liquidus, T.sub.GFA, and T.sub.tough values in
degrees Celcius (.degree. C.) are presented in Table 1. As shown,
for this alloy family T.sub.tough is higher than T.sub.GFA in all
four compositions in Table 1, and both T.sub.tough and T.sub.GFA
are substantially higher than T.sub.liquidus. The degree of
overheating to achieve the high glass-forming ability and
toughness, respectively defined as
.DELTA.T.sub.GFA=T.sub.GFA-T.sub.liquidus and
.DELTA.T.sub.tough=T.sub.tough-T.sub.liquidus, are also presented
for each composition in Table 1.
TABLE-US-00001 TABLE 1 Values for T.sub.liquidus, T.sub.GFA,
T.sub.tough, .DELTA.T.sub.GFA and .DELTA.T.sub.tough for sample
alloys and metallic glasses (in degrees Celcius) Alloy composition
T.sub.liquidus T.sub.GFA T.sub.tough .DELTA.T.sub.GFA
.DELTA.T.sub.tough Ni.sub.69Cr.sub.8.5Nb.sub.3P.sub.16.5B.sub.3
874.degree. C. 1100.degree. C. 1300.degree. C. 226.degree. C.
426.degree. C. Ni.sub.72.5Cr.sub.5Nb.sub.3P.sub.16.5B.sub.3
882.degree. C. 1100.degree. C. 1150.degree. C. 218.degree. C.
268.degree. C.
Ni.sub.68.6Cr.sub.8.7Nb.sub.3P.sub.16B.sub.3.2Si.sub.0.5
884.degree. C. 1150.degree. C. 1250.degree. C. 266.degree. C.
366.degree. C. Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3
881.degree. C. 1125.degree. C. 1250.degree. C. 244.degree. C.
369.degree. C.
Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5
1030.degree. C. 1350.degree. C. 1400.degree. C. 320.degree. C.
370.degree. C.
[0084] Table 2 presents values for T.sub.liquidus, T.sub.GFA,
T.sub.tough, ratios of .DELTA.T.sub.GFA/T.sub.liquidus and
.DELTA.T.sub.tough/T.sub.liquidus for sample alloys and metallic
glasses (in degrees Kelvin).
TABLE-US-00002 TABLE 2 Values for T.sub.liquidus, T.sub.GFA,
T.sub.tough, ratios of .DELTA.T.sub.GFA/T.sub.liquidus and
.DELTA.T.sub.tough/T.sub.liquidus for sample alloys and metallic
glasses (in degrees Kelvin) Alloy composition T.sub.liquidus
T.sub.GFA T.sub.tough .DELTA.T.sub.GFA/T.sub.liquidus
.DELTA.T.sub.tough/T.sub.liquidus
Ni.sub.69Cr.sub.8.5Nb.sub.3P.sub.16.5B.sub.3 1147 K 1373 K 1573 K
0.197 0.371 Ni.sub.72.5Cr.sub.5Nb.sub.3P.sub.16.5B.sub.3 1155 K
1373 K 1423 K 0.189 0.232
Ni.sub.68.6Cr.sub.8.7Nb.sub.3P.sub.16B.sub.3.2Si.sub.0.5 1157 K
1423 K 1523 K 0.230 0.316
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3 1154 K 1398 K
1523 K 0.211 0.320
Fe.sub.67Mo.sub.6Ni.sub.3.5Cr.sub.3.5P.sub.12C.sub.5.5B.sub.2.5
1303 K 1623 K 1673 K 0.246 0.284
Example 2
Melt Overheating to a Temperature Above T.sub.tough and T.sub.GFA
and Subsequently Cooling to an Intermediate Temperature Below
T.sub.tough and T.sub.GFA but Above T.sub.Liquidus
[0085] The effects of overheating the melt to a temperature above
T.sub.tough and T.sub.GFA and subsequently cooling to an
intermediate temperature below T.sub.tough and T.sub.GFA but above
T.sub.liquidus on glass-forming ability and toughness is
investigated for alloy
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3. The alloy is
melted and the melt is overheated to a temperature at least as high
as T.sub.tough and T.sub.GFA, followed by cooling to an
intermediate temperature below T.sub.tough and T.sub.GFA but above
T.sub.liquidus for a fixed period of time, and then quenched to
form a metallic glass.
[0086] FIG. 7 provides a plot showing the effect of cooling to an
intermediate temperature after overheating the melt and prior to
quenching on the glass-forming ability and toughness of alloy and
metallic glass Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3
in accordance with embodiments of the present disclosure. The
critical rod diameters and notch toughness of the metallic glasses
are plotted in FIG. 7.
[0087] As shown in FIG. 7, when the melt is heated to 1250.degree.
C., which is higher than its T.sub.GFA of 1125.degree. C. and equal
to T.sub.tough of 1250.degree. C., and then subsequently quenched,
the critical rod diameter is about 11 mm and the toughness about 85
MPa m.sup.1/2.
[0088] Also, when the melt is heated to 1250.degree. C.,
subsequently annealed at an intermediate temperature of
1100.degree. C., which is slightly below its T.sub.GFA of
1125.degree. C. and well below its T.sub.tough of 1250.degree. C.,
and then quenched, the critical rod diameter drops slightly to
about 9 mm and the toughness drops slightly to about 70 MPa
m.sup.1/2.
[0089] Furthermore, when the melt is heated to 1250.degree. C.,
subsequently annealed at a lower intermediate temperature of
950.degree. C., which is substantially below both its T.sub.GFA and
T.sub.tough, and then quenched, the critical rod diameter remains
high at about 9 mm but the toughness drops sharply to about 30 MPa
m.sup.1/2.
[0090] When the melt is annealed at lower intermediate temperatures
below 950.degree. C. (e.g. 900.degree. C.) and above T.sub.liquidus
after first being heated to 1250.degree. C., both the toughness and
the critical rod diameter appear to also drop sharply to about 30
MPa m.sup.1/2 and 7 mm, respectively.
[0091] Hence, these results suggest that although the threshold
temperatures T.sub.GFA and T.sub.tough are quite high, one does not
have to quench from such high temperature and encounter the
associated adverse effects (e.g. low tool life in the case of die
casting) in order to improve or enhance glass-forming ability and
toughness. Rather, one can cool the melt to an intermediate
temperature (e.g. by transferring it to another cooler reservoir),
such as 1100.degree. C. for
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.64P.sub.16.5B.sub.3 rather than
1250.degree. C., and then quench from that intermediate
temperature, thus avoiding the adverse high-temperature effects
while retaining significant glass-forming ability and
toughness.
[0092] The effect of time on holding the melt isothermally at an
intermediate temperature below T.sub.GFA and T.sub.tough but above
T.sub.liquidus following overheating above T.sub.GFA and
T.sub.tough is also investigated for alloy
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3. The alloy is
melted and the melt is overheated to a temperature of at least as
high as T.sub.tough and T.sub.GFA, followed by cooling to an
intermediate temperature below T.sub.GFA and T.sub.tough but above
T.sub.liquidus where it is held for various periods of time, and
then quenched to form the metallic glass.
[0093] FIG. 8 provides a plot showing the effect of time spent at
an intermediate temperature after overheating the melt and prior to
quenching on the glass-forming ability and toughness of alloy and
metallic glass Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3
in accordance with embodiments of the present disclosure.
[0094] As shown in FIG. 8, the melt is first heated to 1250.degree.
C. and held there for about 180 seconds, then cooled and allowed
just enough time to equilibrate to an intermediate temperature of
1150.degree. C. The alloy melt is quenched immediately after
equilibration at 1150.degree. C., and the critical rod diameter of
the Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3 alloy is
found to be about 9 mm and the toughness of the
Ni.sub.71.4Cr.sub.5.64Nb.sub.3.46P.sub.16.5B.sub.3 metallic glass
about 85 MPa m.sup.1/2.
[0095] When the alloy melt is held for about 450 seconds and also
for about 900 seconds at 1150.degree. C. in addition to the time
required to equilibrate to that temperature and then subsequently
quenched, the critical rod diameter and toughness remain
essentially unchanged.
[0096] This result reveals that no transient processes take place
during isothermal holding at the intermediate temperature. This
result suggests that after the melt is heated to above T.sub.GFA
and T.sub.tough, the melt can be cooled to an intermediate
temperature below T.sub.GFA and T.sub.tough but above
T.sub.liquidus and held there for a long period of time without
affecting the enhanced glass-forming ability and toughness.
Description of Methods of Investigating the Melt Overheating Effect
on Toughness and GFA
[0097] A particular method for producing the example alloys of the
present disclosure involves inductive melting of the appropriate
amounts of elemental constituents in a fused silica crucible under
inert atmosphere to form alloy ingots. Alternatively, the crucible
may also be crystalline silica, a ceramic such as alumina or
zirconia, graphite, or a water-cooled hearth made of copper or
silver. Particular purity levels of the constituent elements were
as follows: Ni 99.995%, Cr 99.996% (crystalline), Nb 99.95%, B
99.5%, Si 99.9999, and P 99.9999%, Fe 99.95%, Mo 99.95%, and C
99.9995%.
[0098] A particular method for producing metallic glass rods from
the alloys of the present disclosure involves re-melting the alloy
ingots in quartz tubes having 0.5 mm thick walls in a furnace under
high purity argon. After processing at specific temperatures, the
melt is rapidly quenching in a room-temperature water bath.
[0099] In various experiments, the melt is heated to an overheating
temperature above the liquidus temperature, followed by quenching
to form metallic glass rods. The critical rod diameter of the
alloys associated with the specific overheating temperature was
determined. Another 3-mm diameter rod was produced for each
overheating temperature following the same procedure, and the
toughness of the 3-mm diameter metallic glass rod was measured.
These data are presented in FIGS. 2-6.
[0100] In various experiments, the melt is first heated to an
overheating temperature, followed by cooling to an intermediate
temperature, and after equilibrating at the intermediate
temperature then quenched. The critical rod diameter of the alloys
associated with the specific overheating and intermediate
temperature was determined. Another 3-mm diameter rod was produced
for each overheating and intermediate temperature following the
same procedure, and the toughness of the 3-mm diameter metallic
glass rod was measured. These data are presented in FIG. 7.
[0101] In various experiments, the melt is first heated to an
overheating temperature, followed by cooling to an intermediate
temperature, and after equilibrating at the intermediate
temperature it was held there for a specific period of time, and
then quenched. The critical rod diameter of the alloys associated
with the specific overheating and intermediate temperatures and
specific period of time was determined. Another 3-mm diameter rod
was produced for each overheating and intermediate temperature and
specific period of time following the same procedure, and the
toughness of the 3-mm diameter metallic glass rod was measured.
These data are presented in FIG. 8.
Test Methodology for Assessing Glass Forming Ability
[0102] The glass-forming ability of each alloy was assessed by
determining the maximum rod diameter, i.e. "critical rod diameter",
in which the amorphous phase of the alloy (i.e. the metallic glass
phase) could be formed when processed by the method of quenching
the alloy melt contained in a quartz tube with 0.5 mm thick walls
in a bath of room temperature water, as described above. X-ray
diffraction with Cu-K.alpha. radiation was performed to verify the
amorphous structure of the alloys.
Test Methodology for Measuring Notch Toughness
[0103] Measurement of notch toughness of the example alloys was
performed on 3-mm diameter amorphous rods at room temperature. The
rods were notched using a wire saw with a root radius of between
0.10 and 0.13 .mu.m to a depth of approximately half the rod
diameter. The notched specimens were placed on a 3-point bending
fixture with span distance of 12.7 mm and carefully aligned with
the notched side facing downward. The critical fracture load was
measured by applying a monotonically increasing load at constant
cross-head speed of 0.001 mm/s using a screw-driven testing frame.
At least three tests were performed, and the variance between tests
is included in the notch toughness plots. The stress intensity
factor for the geometrical configuration employed here was
evaluated using the analysis by Murakimi (Y. Murakami, Stress
Intensity Factors Handbook, Vol. 2, Oxford: Pergamon Press, p. 666
(1987)).
[0104] Having described several embodiments, it will be recognized
by those skilled in the art that various modifications, alternative
constructions, and equivalents may be used without departing from
the spirit of the invention. Additionally, a number of well-known
processes and elements have not been described in order to avoid
unnecessarily obscuring the present invention. Accordingly, the
above description should not be taken as limiting the scope of the
invention.
[0105] Those skilled in the art will appreciate that the presently
disclosed embodiments teach by way of example and not by
limitation. Therefore, the matter contained in the above
description or shown in the accompanying drawings should be
interpreted as illustrative and not in a limiting sense. The
following claims are intended to cover all generic and specific
features described herein, as well as all statements of the scope
of the present method and system, which, as a matter of language,
might be said to fall therebetween.
* * * * *