Note: Descriptions are shown in the official language in which they were submitted.
1~4~3815
AMORPHOUS ALLOYS WITH HIGH CRYSTALLIZATION
TEMPERATURES AND HIGH HARDNESS VALUES
Background of the Invention
A. Field of the Invention
.
The invention relates to amorphous metal alloy composi-
tions, and, in particular, to compositions including substantial
amounts of one or more of the elements of Mo, W, Ta and Nb, which
evidence both high crystallization temperatures and high hardness
values.
B. Description of the Prior Art
Investigations have demonstrated that it is possible
to obtain solid amorphous metals for certain alloy compositions,
and as used herein, the term "amorphous" contemplates "solid
amorphous". An amorphous substance generally characterizes a
noncrystalline or glass substance; that is, a substance substan-
tially lacking any long range order. In distinguishing an amor-
phous substance from a crystalline substance, X-ray diffraction
measurements are generally suitably employed. Additionally, trans-
mission electron micrography and electron diffraction can be used
to distinguish between the amorphous and the crystallizine state.
An amorphous metal produces an X-ray diffraction profile
in which intensity varies slowly with diffraction angle. Such a
profile is qualitatively similar to the diffraction profile of
a liquid or ordinary window glass. On the other hand, a crystal-
line metal produces a diffraction profile in which intensity varies
rapidly with diffraction angle.
These amorphous metals exist in a metastable state.
Upon heating to a sufficiently high temperature, they crystallize
with evolution of a heat of crystallization, and the diffraction
profile changes from one having glassy or amorphous characteristics
to one having crystalline characteristics.
It is possible to produce a metal which is a two phase
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1~48~315
mixture of the amorphous and the crystalline state; the relative
proportions can vary from totally crystalline to totally amorphous.
An amorphous metal, as employed herein, refers to a metal which is
primarily amorphous; that is, at least 50~ amorphous, but which
may have a small fraction of the material present as included
crystallites.
For a suitable composition, proper processing will produce
a metal in the amorphous state. One typical procedure is to cause
the molten alloy to be spread thinly in contact with a solid metal
substrate, such as copper or aluminum, so that the molten metal
rapidly loses its heat to the substrate.
When the alloy is spread to a thickness of about 0.002
inch, cooling rates of the order of 106C/sec may be achieved.
See, for example, R. C. Ruhl, Vol. 1, Mat. Sci. & Eng., pp. 313-
319 (1967), which discusses the dependence of cooling rates upon
the conditions of processing the molten metal. For an alloy of
proper composition and for a sufficiently high cooling rate, such
a process produces an amorphous metal. Any process which provides
a suitably high cooling rate can be used. Illustrative examples
of procedures which can be used to make the amorphous metals in-
clude rotating double rolls, as described by H. S. Chen and C. E.
Miller, Vol. 41, Rev. Sci. Instrum., pp. 1237-1238 (1970), and
rotating cylinder techniques, as described by R. Pond, Jr. and R.
Maddin, Vol. 245, Trans. Met. Soc., AIME, pp. 2475-2476 (1969).
Amorphous alloys containing substantial amounts of one
or re of the elements of Fe, Ni, Co, V and Cr have been de-
scribed by H~ S. Chen and D. E. Polk in United States Patent No.
3,856,513, issued December 24, 1974. Such alloys are quite useful
for a variety of applications. Such alloys, however, are charac-
30 terized by a crystallization temperature of about 425C to 550C
and a hardness of about 600 to 750 DPH (diamond _yramid hardness).
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1~41~815
Summary of the Invention
In accordance with the invention, amorphous alloys are
described having high thermal stability, with crystallization
temperatures ranging from about 650C to 975C and high hardness,
with values ranging from about 800 to 1400 DPH. Two general
compositions have these properties and may be classified as
follows. The first class of compositions is referred to as metal-
metalloid, and has the general formula RrMSXt, where R is at least
one of the elements of molybdenum, tungsten, tantalum, and niobium,
M is at least one of the elements of nickel, chromium, iron,
vanadium, aluminum and cobalt, and X is at least one of the elements
of phosphorus, boron, carbon and silicon, and where "r" ranges from
about 40 to 60 atom percent, "s" ranges from about 20 to 40 atom
percent and "t" ranges from about 15 to 25 atom percent. Preferred
compositions include compositions where "r" ranges from about 45
to 55 atom percent, "s" ranges from about 25 to 35 atom percent
and "t" ranges from about 18 to 22 atom percent. The crystalliza-
tion temperature of the metal-metalloid compositions ranges from
about 800C to 975C and the hardness ranges from about 1000 to
20 1400 DPH.
The second classification is referred to as metal-metal,
and includes refractory metal-base glasses of the general formula
RrNiSTt, where R is at least one of the elements of tantalum, -
niobium and tungsten and T is at least one of the elements of
titanium and zirconium, and where "r" ranges from about 35 to 65
atom percent, "s" ranges from about 25 to 65 atom percent and
"t" ranges from 0 to about 15 atom percent. Preferred compositions,
where "t" is 0, include the composition region encompassed from
Ta35NiSW65-s to Ta45Nisw55-s~ where "s" ranges from about 35 to
30 45 atom percent, and the composition TarNis, where "r" ranges
from about 35 to 50 atom percent and "s" ranges from about 50 to
65 atom percent. The crystallization temperature of the metal-metal
~6)48815
compositions ranges from about 650C to 800C, and the hardness
ranges from about 800 to 1125 DPH.
Such metal glasses, whether metal-metalloid or metal-
metal, are particularly useful for heat resistant applications at
high temperatures (about 500 to 600C). Possible applications
include use of these materials as electrodes in certain high
temperature electrolytic cells, and as reinforcement fibers in
composite structural materials.
Brief Description of the Drawing
FIG. 1 is a ternary phase diagram in atom percent of
the metal-metalloid system R-M-X, where R is one or more of the
elements of Mo, w, Ta and Nb, M is one or more of the elements of
Ni, Cr, Fe, V, Al and Co and X is one or more of the elements of
P, B, C and Si; and
FIG. 2 is a ternary phase diagram in atom percent of
the metal-metal system Ta-W-Ni.
Detailed Description of the Invention
A. Metal-Metalloid Compositions
Most liquid-quenched glass compositions in various
metal-metalloid systems have evidenced crystallization temperatures
of about 425C to 550C. In accordance with the present invention,
compositions represented by the general formula RrMSxt have crys-
tallization temperatures ranging from about 800C to 975C. In
the formula, R is at least one of the refractory metals of Mo,
W, Ta and Nb, M is at least one of the metals of Ni, Cr, Fe, V,
Al and Co and X is at least one of the metalloids of P, B, C
and Si. The purity of all elements described is that found in
normal commercial practice.
For Mo-base compositions, amorphous alloys are formed in
systems containing at least about 25 atom percent of Ni, Cr, Fe,
V or Al Typical compositions in atom percent are Mo52CrlOFelONig-
P12B8 and M40Cr25Fel5B8C7Sis- Such amorphous alloys, or glasses,
- 1~)48815 :
possess high thermal stability as revealed by DTA (_ifferential
thermal analysis) investigation. The temperatures for crystalli-
zation peaks, Tc, can be accurately determined from DTA by slowly
heating the glass sample and noting whether excess heat is evolved
at a particular temperature (crystallization temperature) or
whether excess heat is absorbed over a particular temperature range
(glass transition temperature). In general, the less well-defined
glass transition temperature Tg is considered to be within about
50 below the lowest, or first, crystallization peak, TC1~ and,
as is conventional, encompasses the temperature region over which
the viscosity ranges from about 1013 to 1014 poise.
The various Mo-base glasses with about 25 to 32 atom
percent Ni, Cr, Fe, Al (either single or combined), plus about 12
atom percent P and about 8 atom percent B, crystallize in the range
of about 800C to 900C. Substitution of P by C or Si by 6 to
8 atom percent increases Tc by about 40C to 50C. Further thermal
stability is achieved by partial substitution of W for Mo. Alloys
containing about 8 to 20 atom percent W have crystallization tempera-
tures in the range of about 900C to 950C.
High Tg glass-forming compositions exist also in W-base
alloys. Typically, these alloys contain about 15 to 25 atom per-
cent Mo, about 25 atom percent Ni, Fe, and Cr, and about 20 atom
percent P, B, C and Si. These alloy glasses are remarkably stable
and crystallize at temperatures in excess of 950C. For example,
one glass composition, W40Mol5CrlsFesNi5P6B6C5Si3, evidences two
crystallization peaks, 960C and 980C, in a DTA trace. However,
as W content is increased to beyond 40 atom percent, it becomes
increasingly difficult to form a glass.
The glasses are formed by cooling a melt at a rate of
about 105 to 106C/min. A variety of techniques are available,
as is well-known in the art, for fabricating splat-quenched foils
and rapid-quenched continuous ribbon, wire, etc.
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Glasses evidencing high Tg properties as described
above also evidence high ductility and high corrosion resistance
compared to crystalline or partially crystalline samples. In
addition, these amorphous alloys have rather high hardness values.
Typically, the hardness for Mo- and W-base glasses ranges from about
1000 to 1400 DPH (diamond _yramid hardness). This is to be com-
pared with amorphous alloys of metal-metalloid compositions
comprising substantial amounts of Fe or Fe-Ni, but lacking any
substantial amount of refractory metal. For these latter alloys,
10 the hardness usually is about 600 to 750 DPH.
Shown in FIG. 1 is a ternary phase diagram of the system
R-M-X, where R is Mo, W, Ta and/or Nb, M is Ni, Cr, Fe, V, Al and/or
Co, and X is P, B, C and/or Si. The polygonal region designated
a-b-c-d-e-f-a encloses the glass-forming region that also includes
composition having high Tg and high hardness. Outside this composi-
tion region, either a substantial degree of amorphousness is not
attained or the beneficial properties are unacceptably reduced.
The compositional boundaries of the polygonal region
are described as follows: "r" ranges from about 40 to 60 atom
percent, "s" ranges from about 20 to 40 atom percent, and "t"
ranges from about 15 to 25 atom percent. The highest values of
Tg and hardness are formed in compositions represented by the
"line" g-h, that is, in which "r" ranges from about 45 to 55 atom
percent, "s" ranges from about 25 to 35 atom percent, and "t"
ranges from about 18 to 22 atom percent (more specifically, "t"
is about 20 atom percent). Accordingly, this latter composition
range is preferred. Maximum benefit is derived for compositions
where R is Mo and/or W and M is Ni, Fe and/or Cr.
B. Metal-Metal Compositions
Also in accordance with the present invention, alloys
providing consistent glass-forming behavior plus high thermal
stability include the binary systems Ta-Ni, Nb-Ni and ternary
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104~815
modifications with W, Ti and/or Zr. Here, the compositions of
interest may be described by the general formula RrNiSTt, where
R is Ta, Nb and/or W and T is Ti and/or Zr. Such compositions
have crystallization temperatures ranging from about 650C to
800C.
Ta-Ni binary glasses crystallize in the range 760c to
780C, which is about 100C higher than those for Nb-Ni glasses.
The partial substitution of W for Ta raises Tc only slightly
(about 15C to 20C) and does not change appreciably with
increasing W content. On the other hand, partial addition of
Ti or Zr tends to lower Tc.
For the binary compositions of TarNis and NbrNiS, glasses
are formed where "r" ranges from about 35 to 65 atom percent and
"s" is the balance, that is, 35 to 65 atom percent (t=O). Optimum
properties are obtained in the system TarNis, where "r" ranges
from about 35 to 50 atom percent and "s" ranges from about 50 to
65 atom percent.
For the ternary composition region from Ta35NiSW65-S
to Ta4sNisW55_s, a glass-forming region that is consistent with
20 high Tg and high hardness is shown in FIG. 2, which is a ternary
phase diagram of the system Ta-W-Ni. The polygonal region desig-
nated a-b-c-d-a encompasses the optimum glass-forming region.
Outside this composition region, either a substantial degree of
amorphousness is now attained or the beneficial properties are
unacceptably reduced. In FIG. 2, "s" ranges from about 35 to
45 atom percent.
Since the addition of Ti or Zr tends to lower Tc, then
such addition should not exceed about 15 atom percent, and
preferably 10 percent, to retain the advantages of high Tg and
30 high hardness.
In general, the hardness of the foregoing systems ranges
from about 800 to 1125 DPH.
1~488~5
EXAMPLES
A. Metal-Metalloid Compositions
A pneumatic arc-splat unit for melting and liquid
quenching high temperature reactive alloys was used. The unit,
which was a conventional arc-melting button furnace modified to
provide "hammer and anvil" splat quenching of alloys under inert
atmosphere, included a stainless steel chamber connected with a
4 inch diffusion pumping system. The quenching was accomplished
by providing a flat-surfaced water-cooled copper hearth on the
floor of the chamber and a pneumatically driven copper-block hammer
poised above the molten alloy. As is conventional, arc-melting
was accomplished by negatively biasing a copper shaft provided
with a tungsten tip inserted through the top of the chamber and
by positively biasing the bottom of the chamber. Alloys containing
P were prepared by sintering powder ingredients followed by arc-
melting to homogenization. All other alloys were prepared directly
by repeated arc-melting of constituent elements. A single alloy
button (about 200 mg) was remelted and then "impact-quenched" into
a foil about 0.004 inch thick by the hammer situated just above
the molten pool. The cooling rate attained by this technique
was about 105 to 106C/sec. The foils were checked for amorphous-
ness by X-ray diffraction and DTA.
The impact-quenched foil directly beneath the hammer
may have suffered plastic deformation after solidification.
However, portions of the foil formed from the melt spread away
from the hammer were undeformed and hence suitable for hardness
and other related tests. Hardness was measured by the diamond
pyramid technique, using a Vickers-type indenter consisting of
a diamond in the form of a square-based pyramid with an included
angle to 136 between opposite faces.
The crystallization temperatures and hardness values
are shown in Table I for a variety of metal-metalloid compositions.
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16~488~5
TABLE I
CRYSTALLIZATION TEMPERATURES (TC1) AND HARDNESS (DPH) MEASUREMENTS
FOR METAL-METALLOID COMPOSITIONS
Composition Hardness,
Example atom % _cl~__C DPH
1 M48Cr32Pl2B8 878 ----
2 Mo48Fe32Pl2B8 828 ----
3 Mo 48Ni 32 P12B8 805 ----
4 Mo5oFeloAl2oploB7si3 837 1026
10 5 MO52Crl4Fel4Pl2B8 863 1260
6 MO52crloFeloNi8Pl2 8 831 1234
7 Mo40Cr25Fel5B8C7Si5 913 ____
8 M40Wlocr30Pl5B5 881 ----
9 Mo35W20crl8Fe7p6B6c5si3 950 --
Mo40W15Crl8Fe7P6B6C5Si3 894 ____
11 M35W15Cr25Fe5P6B6C5Si3 920 ----
12 Mo40W8Cr24Fe8P6B6C5Si3 902 1392
13 Mo30Nb2ocr3op8B7si5 9 3 1187
14 w30Mo25Crl8Fe7p6B6c5si3 5 1350
2015 W35MO20Crl5Fe5Ni5P6B6C5Si3 946 1378
16 W40MO15Crl5Fe5Ni5P6B6C5Si3 960 1396
B Metal-Metal Compositions
.
Various metal-metal compositions were prepared and
measured as described above. The results of the crystallization
temperature and hardness are shown in Table II.
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TABLE II
CRYSTALLIZATION TEMPERATURES (TC1) AND HARDNESS (DPH) MEASUREMENTS
FOR METAL-METAL SYSTEMS
Composition, Hardness,
Example atom % _cl~ C DPH
17 55 45 780 1111
18 Ta50Ni50 767941, 1115
19 Ta45Ni45Wlo 818, 969
Ta45Ni40Wl5 796 ____
lo 21 Ta45Ni35W2o 800 ____
22 Ta35Ni45W2o 791 ____
23 Ta35Ni35w3o 800 ____
24 Ta55Ni35Zrlo 683 ____
Ta55Ni35TilO
26 Ta50Ni4oTilo 717 ____
27 Nb65Ni35 662 960
28 Nb6oNi4o 680 923
29 Nb50Ni50 653 863
Nb60Ni28Til2 662 - --
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