Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to metallurgical compositions
embodying metal carbides, in particular, hard metal carbides, and
is especially concerned with a composition that can be tailored
as to characteristics including that of being nonmagnetic or
magnetic while remaîning hard and wear resistant.
Many hard wear resistant metallurgical compositions embody-
ing hard metal carbides are known, and most thereof are quite
satisfactory for the intended use. An application for hard wear
resistant carbide materials in connection with which there has
not, heretofore, been satisfactory materials are those uses in
which the hard wear resistant material must be nonmagnetic.
For example, machines in which magnetic tapes are employed
often require wear resistant guides and the like for supporting
and guiding the tapes. Still other cases will suggest themselves
in which a hard wear resistant, or structurally strong, member
is required where magnetic interactions are undesirable and in
these cases, also, nonmagnetic carbide materials would be highly
useful.
While the metallurgical composition according to the present
invention can, as will be shown, be made nonmagnetic, magnetic
variations of the composition have also been found highly useful
in places where the composition must be hard and wear resistant
and/or noncorrosive and/or noncontaminating or where the
material must be extremely hard as in connection with a tool -
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composltlon O
With the foregoing in mind, a primary objective of the
present invention is the provision of a metallurgical composition
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embodying hard metal carbides which has the possibility of being
formulated so as to be nonmagnetic but which will retain the -
desirable attributes o~ hard carbide metallurgical compositions.
Another object is the provision of a metallurgical composi- -
tion of the nature referred to which can be so co~pounded prior
to the formation thereof as to be either nonmagnetic or magnetic
when completed. -
A still further object is the provision of a metallurgical
composition embodying hard metal carbides which is satisfactory
for use as a ~ool and which can be compounded to vary in magnetic
properties at room temperature to the state of being nonmagnetic,
BRIEF SUMMARY OF THE INVENTION:
The metallurgical composition according to the present -
invention is concerned primarily with tungsten, titanium, nickel, ~ -
carbon compositions and to which may be added a certain amount of
chromium and other carbides. The composition of the present
invention can be compounded in such a manner as to be either
nonmagnetic or magnetic while still having the desirable charac-
teristics of hard wear resistant cemented carbides.
Thus, in accordance with the present teachings, there is
provided a sintered cemented carbide product the compositions of
which comprises tungsten carbide, titanium carbide and a binder
alloy comprising tungsten-nickel in which the ratio o~ the
tungsten in the binder alloy to the binder is from 2 to 28 per
cent by weight. By one aspect the above product is non-ferro-
magnetic and has a ratio of tungsten in the binder alloy to the
binder alloy of 15 to 28 per cent by weight. By another aspect
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the above product has ferromagnetic properties and has a ratio
of tungsten in the binder alloy to the binder alloy of less than
14 per cent by weight.
The hard metal carbides, including tungsten carbide and
titanium carbide, are nonmagnetic so that a metallurgical composi-
tion embodying hard metal carbides can be made provided a suitable
metal binder system is employed which is also nonmagnetic.
A binder metal for a cemented carbide composition should be
tough and should also wet the carbide. A nickel binder system
is, thus, a preferred binder because nickel wets the carbide
compounds and is tough. Nickel, furthermore, although being
itself ferromagnetic, can be alloyed with tungsten, which is
also nonmagnetic, without undergoing a phase change upon heating
or upon cooling from the liquid phase over a relatively broad
alloying range and an alloy of this material can be selected
which is nonmagnetic. By nonmagnetic, a material is referred to
which has magnetic permeability near unity and which is lacking
in the ability to become magnetized or to exhibit induced `~ `
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magnetism, namely, a material with ~ Oersted coercive force. ~ :
When the more common binder metal, cobalt, is employed as
a binder, and the composition is adjusted to be, or to approach ~i
being, nonmagnetic, the binder phase of the composition becomes
extremely brittle clue to the formation of Co3W3C and the composi-
tion is, thus, defective for many uses. The present invention
overcomes this objection by including titanium in the composition
and employing nickel or nickel and chromium as the basic binder
metal.
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When titanium, tungsten carbide and nickel, with or without
some chromium, are admixed in powder form, compacted and hea~ed ~ :
so that a liquid phase is formed containing W, C and some or
all of the titanium in solution, then the carbon can associate
itself with the titanium to form titanium carbide or a solid
solution of TiC with WC, or both, because the free energy of
formation for forming TiC is more favorable than for forming WC.
Thus, tungsten is freed during sintering to alloy with a binder
metal or metals.
The mass balance is calculated so the stoichiometric excess
W during sintering can alloy with the nickel and result in a
magnetic or nonmagnetic binder alloyO The carbon balance with :
respect to the titanium must take into account the non-stoichio-
metric nature of TiC as less than one carbon atom per titanium
atom is sufficient to form titanium carbide. -
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Thus, by including titanium in the mixture, carbon is
removed from the melt because of the affini-ty of titanium for the
carbon, and an alloy of nickel and tungsten and/or titanium is
formed during sintering. It has been found that a fairly wide
range of compositions according to the present invention will
result in the production of a nonmagnetic alloy having the same
crystal structure as pure nickel, namely, face centered cubic.
While carbon deficient tungsten carbide can be employed
with a nickel binder to yield a nickel-tungsten alloy binder
after sintering, extremely close control of the respective levels
of nickel and carbon are required and an impractical control
situation arises.
It has been found that small, less than 0.5 weight per cent,
titanium metal additions as described herein very effectively
inhibit grain growth during sintering and result in a Eine
grained structure and consequently improved strength.
A particular advantage of the present invention is to be
found in the fact that, once the analysis of the WC component
is ascertained to reveal the amount of carbon in the WC component,
the amount of Ti to add to the composition can readily be
calculated. Formulation and control are thus greatly simplified~
The exact nature of the present invention will become
more apparent upon reference to the following specification
giving specific examples and to the accompanying drawings in which: -
Figure 1 is a graph giving weight per cent titanium tocharge.
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Figure 2 is a part of the nickel-tungsten phase diagram
showing, in particular, the magnetic transformation character-
istics of nickel-tungsten alloys.
DETAILED DESCRIPTION OF THE INVENTION:
The compositions according to the present invention can be
compounded by closely analyzing each constituent for the carbon,
oxygen, nitrogen and metallic impurities. The amount of Ti
required to release the quantity of tungsten from the tungsten
carbide to produce the nickel-tungsten alloy composition can
then be calculated or determined experimentally.
In making the calculations, the tungsten level desired in
the binder and the nickel content are established and the
equations giving the desired amount of titanium, or tungsten,
are solved.
In preparing the compositions, the powders charged in the
mixture before sintering have about the following percentages `
by weight: ~-
Nickel - 3.0 - 25.0
Titanium - .05 - 2.0
Tungsten Carbide- Balance
In addition chromi~m may also be included in the range of 0.0
to 2,0 per cent by weight.
Figure 1 shows how much titanium to charge with tungsten
carbide having the indicated total carbon content and negligible
oxygen, nitrogen and metallic impuritles. In the graph, the
weight % of Ni in the composition is always 10, The other 90%
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of the composition is made up of WC and Ti. Thus, for example,
at 1 wt. % Ti, there will be 89 wt. % WC. Each line of the
graph shows ~he amount of Ti to be supplied to obtain the
indicated weight % of W in the binder.
TABLE I
Weight % Titanium to charge to a 10 Wt. % Nickel balance
tungsten carbide composition (the WC having 6.10 Wt. % carbon `-
content and negligible impurities) to obtain the calculated 10,
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20, or 25 Wt. % W/(W ~ Ni) in the binder alloy as a function
of carburization of the titanium additionO
Est.
Calculated Wt. % Atom
Wt. % Wto % Ti to Ratio
Nickel W/(~ ~ Ni~ Char~e C/Ti
0.283 0.6
0.240 0O7
0.208 0.8
0O187 0.9
0.879 0.6
0.748 0O7
0.654 0.8
0.585 0O9
1.242 0.6
1.077 0,7
0.940 0.8
0.831 0.9
Chromium metal additions may be made to the composition,
as will be explained more fully hereinafter, and help to further `
inhibit grain growth and also to stabilize the nonmagnetic -
properties when the composition is to be nonmagnetic. Chromium
has produced good results and for a 10 weight % nickel composi-
tion, a 1 weight % chromium level produced satisfactory results.
The chromium metal addition is not essential to achieve
nonmagnetic properties. It can react with and take up some of
the carbon by forming carbides of chromium, and it can also
alloy with the hickel.
Titanium can be supplied in the form of powders of titanium
metal, any alloy of titanium with nickel, not necessarily TiNi
eutetic composition or as a hydride of titanium. The last
mentioned form is preferred because it is less reactive than
the pure metal and can be milled readily. Also, it is less
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expensive than an alloy of titanium with nickel while, urther-
more, the hydrogen that is evolved from titanium hydride during
the early stagas of sintering can be beneficial because it can
be effective for reducing surface oxides, particularly those
which form on nickel.
The nonmagnetic capability of the type of composition
disclosed herein is important but there are other applications
for the composition wherein chemical inertness and strength and
wear resistance are the principal characteristics desired.
Nonmagnetic grades of the composition, as mentioned, are
particularly useful for magnetic tape guides and the like. Both
magnetic and nonmagnetic gradés of the composition are useful
as cutting tools and the like and also as tools for use in glass
making and the like where cobalt contamination is detrimental,
The following chart gives a number of examples of composi-
tions, the first five thereof being nonmagnetic grades and the
last two being magnetic grades:
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The last two columns of the chart, the first of which
gives transverse rupture strength, alld the other of which gives
hardness on the Rockwell 'lA" scale, have two values for each
composition. The reason for this is that the upper number of
each pair is the value obtained when the composition is compacted
and vacuum sintered and the second value is for a vacuum sintered
speciment subjected to reheating in the presence of a high
pressure inert gas.
In making any of the compositions referred to above, con- -
ventional milling procedures may be followed. A tungsten
carbide lined mill with tungsten carbide milling media therein
is preferably employed to avoid contamination. This mixture is
milled for about ~ to 15 days and then processed in a conven-
tional manner to arrive at a sintered end product.
Sintering may be accomplished at from about 1350 to about
1550 degrees Centigrade for a period of about 0~25 to 2.0 hours
at 0.02 to 0.75 Torr.
It will be understood that during sintering tungsten
released from tungsten carbide by the capturing of the carbon
by titanium, can form what is referred to as Eta phase in com-
bination with nickel and carbon~ or if the composition contains
chromium, with chromium and carbon.
Such a phase might be represented as Ni3W3C. This material
will not, if present in small amounts, detract from the physical
or magnetic properties of the material and serves as a part of
the binder of the sintered composition.
Modifications may be made within the scope of the appended
claims.
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