Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
` 1078225
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The present invention relates to metallurgical
compositions embodying metal carbi`des, in particular, hard
metal carbide6, and is especially concerned with a composition
that can ~e tailored as to characteristics including that of
being nonmagnetic or magnetic while remaining hard and wear
resistant.
Many hard wear resistant metallurgical compositions
embodying 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 non-
magnetic 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 noncorrosi~e and/or noncontaminating or
where the material must be extremely hard as in connection with
a tool composition.
With the foregoing in mind, a primary objective of the
present invention is the provision of a metallurgical composition
embodying hard metal carbides which has the possibility of
being formulated so as to be nonmagnetic but which will retain
the desirable attributes of hard carbide metallurgical
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compositions.
Another ohject is the provision of a metallurgicalcomposition of the nature referred to which can ~e so compounded
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 tool 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 s~ill having the desirable
characteristics 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 of
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-
ferromagnetic 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 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
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composition embodying hard metal carbides can be made provided
a suitable metal binder sy-stem 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 magnetism, namely, a material with 0 Oersted
coexcive force.
When the more common binder metal, cobalt, is employed
as a binder, and the composition is adjusted to be, or to
approach being, nonmagnetic, the binder phase of the composition
becomes extremely br;ttle due to the formation of Co3W3C and
the composition 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.
When titanium, tungsten carbide and nickel, with or
without some chromium, are admixed in powder form, compacted
and heated 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
then for forming WC, Thus, tungsten is freed during sintering
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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 alloy. The carbon balance
with respect to the titanium must take into account the non-
stoichiometric nature of TiC as less than one carbon atom
per titanium atom is sufficient to form titanium carbide.
Thus, by including titanium in the mixture, carbon
is removed from the melt because of the affinity 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 composïtions 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 fine 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. Formu~ation and control are thus
greatly simplified.
The exact nature of the present invention will become
more apparent upon reference to the following specificatïon
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giving specific examples and to the accompanying drawings in
which:
Figure 1 is a graph giving weigfit per cent titanium
to charge.
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- Balan~e
In addition chromium 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 impurities. In the
graph, the weight % of Ni in the composition is always 10.
The other 90% of the composition is made up of WC and Ti.
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Thus, for example, at 1 wt~ ~ Ti, there will be 89 wt~ %
WC. Each line of the graph shows the amount of Ti to be
supplied to obtain the indicated weight % of W in the b;nder.
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 impuritiesl to obtain the calculated 10,
2a, or 25 Wt. ~ W/(W + ~î~ in the binder alloy as a function
of carburization of the tïtanium addition.
Est.
Calculated Wt. % Atom
Wt. ~ Wt. % Ti to Ratio
Nickel W/(W + Ni~ Char~e C/Ti
0.283 0.6
la 10 0.240 0.7
0.208 0.8
0.187 0.9
0.879 0.6
2a 0.748 0.7
la 20 0.654 0.8
0.585 0.9
1.242 0.6
1.077 0.7
la 25 0.940 0.8
0.831 0.9
Chrom;um 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 non-
magnetic properties when the composition is to be nonmagnetic.
Chromium has produced good results and for a 10 weight %
nickel composition, 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 nickel.
Titanium can be supplied in the form of powders of
titanium metal, any alloy of titanium with nickel, not
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,
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necessarily TiNi eutetic composition or as a hydride of
titanium~ The last ment;oned form is preferred because it is
less reactive then the pure metal and can be milled readily.
Also, it is less expensive than an alloy of titanium with
nickel while, furthermore, the hydrogen that is evolved from
titanium hydride during the early stages 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 grades 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 num~er of examples of
compositions, 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, and the otHer of which giYeS
hardness on the Rockwell "A" 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,
conventional m;lling 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 4 to 15 days and then processed in a
conventional 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 ~y the capturing of the carbon
by titanium, can form what is referred to as Eta phase in
combination 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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