U.S. patent number 3,660,082 [Application Number 04/787,435] was granted by the patent office on 1972-05-02 for corrosion and wear resistant nickel alloy.
This patent grant is currently assigned to The Furukawa Electric Company Limited. Invention is credited to Masaru Ikeda, Akira Negishi, Kiyoshi Takayanagi.
United States Patent |
3,660,082 |
Negishi , et al. |
May 2, 1972 |
CORROSION AND WEAR RESISTANT NICKEL ALLOY
Abstract
Corrosion and wear resistant nickel alloys are disclosed wherein
1-50 at. % of the Ni atoms is substituted by one or more of Fe, Mo,
Co and Cr and 0-10 at. % of Ti atoms is substituted by Zr. The Ni
atoms and Ti atoms are contained in an alloy consisting of 45-53
at. % of Ti and the remainder of Ni.
Inventors: |
Negishi; Akira (Tokyo,
JA), Takayanagi; Kiyoshi (Tokyo, JA),
Ikeda; Masaru (Tokyo, JA) |
Assignee: |
The Furukawa Electric Company
Limited (Tokyo, JA)
|
Family
ID: |
25141463 |
Appl.
No.: |
04/787,435 |
Filed: |
December 27, 1968 |
Current U.S.
Class: |
420/451; 420/459;
420/581; 420/588; 420/441; 420/580; 420/586 |
Current CPC
Class: |
C22C
19/007 (20130101); C22F 1/006 (20130101); C22C
14/00 (20130101) |
Current International
Class: |
C22F
1/00 (20060101); C22C 14/00 (20060101); C22C
19/00 (20060101); C22c 015/00 (); C22c
019/00 () |
Field of
Search: |
;75/134,135,170,171,175.5 ;148/32,32.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Nuclear Science Abstracts, Vol. 20 No. 2, 1966 page 300 .
Journal of Metals, Sept. 1950, pages 1173-1176, Duwez et al. .
Ocean Engng., Vol. 1 Pergamon Press 1968 pages 105-120 .
Wang, Proceedings of the First International Conf. on Fracture,
1965 Vol. 2 pp 899-908.
|
Primary Examiner: Lovell; Charles N.
Claims
What is claimed is:
1. A corrosion and wear resistant nickel alloy produced by
replacing 1-50 at. % of the nickel atoms of intermetallic compound
Ni-Ti alloy consisting essentially of 45-53 at. % titanium and the
remainder Ni by a metal selected from the group consisting of Mo
and Cr; and by replacing 0-10 at. % of the Ti atoms of said Ni-Ti
alloy by Zr, said alloy having excellent corrosion and wear
resistance and a high mechanical strength at high temperature and
room temperature and being hot- and cold-workable and free from
transformation caused by temperature or by working within the
practical temperature range.
2. The corrosion and wear resistant nickel alloy of claim 1,
consisting of 47-52 at. % of Ti and the remainder of Ni, 1-25 at. %
of Ni atoms being substituted by a metal selected from the group
consisting of Mo and Cr, said alloy being easy to hot- and
cold-work.
3. The corrosion and wear resistant nickel alloy of claim 1,
consisting of 48-52 at. % of Ti and the remainder of Ni, 1-20 at. %
of Ni atoms being substituted by a metal selected from the group
consisting of Mo and Cr, said alloy being easier to hot- and
cold-work than the nickel alloy of claim 2.
4. The corrosion and wear resistant nickel alloy of claim 1,
wherein 0.1-7 at. % of Ti atoms are substituted by Zr, said alloy
having a high mechanical strength.
5. The corrosion and wear resistant nickel alloy of claim 1,
consisting of 49.5-50.5 at. % of Ti and the remainder of Ni, 2-20
at. % of Ni atoms being substituted by a metal selected from the
group consisting of Mo and Cr, said alloy having excellent
corrosion resistance and being particularly easy to hot- and
cold-work.
6. The corrosion and wear resistant nickel alloy of claim 1,
consisting of 50.7-52 at. % of Ti and the remainder of Ni, 1-20 at.
% of Ni atoms being substituted by a metal selected from the group
consisting of Mo and Cr, and 0.1-5 at. % of Ti atoms are
substituted by Zr, said alloy having a high mechanical strength and
excellent corrosion resistance and being easy to hot- and
cold-work.
7. The corrosion and wear resistant nickel alloy of claim 1,
consisting of 48-49 at. % of Ti and the remainder of Ni, 1-20 at. %
of Ni atoms being substituted by a metal selected from the group
consisting of Mo and Cr, said alloy being capable of improving its
mechanical strength by means of quenching and tempering
processes.
8. The corrosion and wear resistant nickel alloy of claim 1,
consisting of 48-48.6 at. % of Ti and the remainder of Ni, 1-5 at.
% of Ni atoms being substituted by a metal selected from the group
consisting of Mo and Cr, said alloy being capable of further
improving its mechanical strength by means of quenching and
tempering processes.
9. The corrosion and wear resistant nickel alloy of claim 1,
wherein 1-50 at. % of the nickel atoms are replaced by Mo only and
5-95 at. % of said replacing Mo atoms are replaced by at least one
of Fe and Co, said alloy having excellent corrosion resistance and
cold workability.
10. The corrosion and wear resistant nickel alloy of claim 9,
wherein said replacing Mo atoms are replaced by Fe and Co such that
Mo, Fe and Co have an atomic ratio of 1:1:1.
11. The corrosion and wear resistant alloy of claim 1, wherein 1-50
at. % of the nickel atoms are replaced by Mo only and 5-95 at. % of
said replacing Mo atoms are replaced by Fe only, said alloy having
excellent corrosion resistance and cold workability.
12. The corrosion and wear resistant alloy of claim 11, wherein
said replacing Mo atoms are replaced by Fe such that Mo and Fe have
an atomic ratio of 2:3.
13. The corrosion and wear resistant nickel alloy of claim 1,
wherein 1-50 at. % of the nickel atoms are replaced by Mo only and
5-95 at. % of said replacing Mo atoms are replaced by Co, said
alloy having the most excellent corrosion resistance and cold
workability.
14. The corrosion and wear resistant nickel alloy of claim 13,
wherein the atomic ratio between Mo and Co is 2:3.
15. The corrosion and wear resistant nickel alloy of claim 1,
wherein 1-50 at. % of the nickel atoms are replaced by Mo and Cr
whose atomic ratio is 1:1.
16. The corrosion and wear resistant nickel alloy of claim 1,
wherein 1-50 at. % of the nickel atoms are replaced by Cr only,
said alloy having the most excellent wear resistance.
Description
This invention relates to an improvement of intermetallic compound
NiTi and nickel-titanium alloys of substantially the same
composition as that of NiTi and particularly to Ni-Ti alloys free
from transformation caused by a temperature change or by working
within the practical temperature range and having a high mechanical
strength at room temperature and high temperature, excellent
anti-corrosive and wear resisting properties and plasticity.
The intermetallic compound NiTi and Ni-Ti alloys having
substantially the same composition as that of NiTi are known to
have excellent mechanical strength and vibration damping property
owing to special transformation occurring at about room
temperature. It is known that NiTi and Ni-Ti alloys of
substantially the same construction as that of NiTi have
considerable plasticity unlike any other type of intermetallic
compound. In view of the above mentioned peculiar properties, NiTi
and Ni-Ti alloys having substantially the same composition as that
of NiTi are used for machines and apparatuses for space
development, temperature sensing devices, various kinds of
underwater weapons, tools, etc. However, NiTi and Ni-Ti alloys of
substantially the same composition as that of NiTi have the
disadvantages that they are not sufficiently resistant to some
kinds of acids and have not enough mechanical strength at high
temperature, that the dimensions of their product considerably vary
above and below the transformation temperature which is near room
temperature, and that they are transformed by working at a
temperature higher than said transformation temperature and if they
are heated to a temperature higher than a given temperature, said
transformation returns to the original condition so that they
return to the configuration prior to the working. As above
mentioned, NiTi and Ni-Ti alloys of substantially the same
composition as that of NiTi have a considerable plasticity unlike
any other type of intermetallic compound, but their rate of
reduction by rolling is limited to about 20 percent, beyond which
cracks will develop therein. NiTi and Ni-Ti alloys of substantially
the same composition as that of NiTi are highly active at high
temperature so that it is impossible to melt them in a crucible.
Thus, to manufacture product of these NiTi and Ni-Ti alloys of
uniform quality they must be subjected repeatedly to complicated
arc melting process in the same manner as for titanium alloys in
general. Moreover, such arc melting process cannot make use of
scraps of Ni or Ti or their alloys and therefore makes the
manufacturing cost high. Owing to the above described defects NiTi
and Ni-Ti alloys of substantially the same composition as that of
NiTi have not practically been used for apparatuses and parts to be
used in the chemical and mechanical industrial fields.
An object of the invention is to provide corrosion and wear
resistant, high strength nickel alloys for use for general
apparatus and parts for the chemical and machinery industries by
preventing transformation caused by a temperature change or by
working within the practical temperature range and by improving
mechanical strength at room temperature and high temperature and
corrosion and wear resistance.
Another object of the invention is to provide a melting and casting
method in which scraps of raw materials and alloys can be used and
an ingot substantially free from segregation can be produced at a
low cost simply by melting in crucible.
Still another object of the invention is to provide a method of
heat treating the alloy according to the invention for further
improvement of mechanical strength.
The inventors have investigated on changes of the properties of
NiTi and Ni-Ti alloys of substantially the same composition as that
of NiTi by substituting a part of the Ni and Ti atoms by various
kinds of elements and found out that substitution of 1-50 at. % of
Ni atom contained in an alloy consisting of 45-53 at. % of Ti and
the remainder of Ni by one or more of Fe, Mo, Co and Cr
(hereinafter called "M") has yielded the surprising result that
transformation caused by temperature change or by working within
the practical temperature range can be prevented and mechanical
strength at room temperature and high temperature and corrosion and
wear resistance can be improved. The inventors have also found out
that substitution of 1-50 at. % of the Ni atoms by M and
substitution of 0-10 at. % of Ti atoms by Zr yielded the result
that the above mentioned mechanical strength at room temperature
and high temperature and corrosion resistance can further be
improved.
Other objects, features and advantages of the invention will become
apparent from the following specification, in conjunction with the
accompanying drawings in which:
FIG. 1 is a ternary phase diagram; and
FIG. 2 shows curves illustrating the relation between tempering
temperature and hardness of the alloys according to the
invention.
The range of the compositions of the alloys according to the
invention will now be explained with reference to FIG. 1 showing a
ternary phase diagram where
Point A ((Ti+Zr) 45 at. %, M 0.55 at. % and the remainder Ni),
Point B ((Ti+Zr) 53 at. %, M 0.47 at. % and the remainder Ni),
Point C ((Ti+Zr) 53 at. %, M 23.5 at. % and the remainder Ni),
Point D ((Ti+Zr) 45 at. %, M 27.5 at. % and the remainder Ni)
are connected in the order of A, B, C, and D with straight lines to
form a quadrilateral within which lies the compositions of the
alloys according to the invention, and (Ti+Zr) designates a
composition in which 0-10 at. % of the Ti atoms is substituted by
Zr.
The reason why 1-50 at. % of Ni atoms contained in the alloys
according to the invention consisting of 45-53 at. % of Ti and the
remainder of Ni is substituted by M (the atomic ratio of Ni:M lies
within a range of 99:1-50:50) is that in the ternary phase diagram
shown in FIG. 1 a brittle and injurious intermetallic compound
Ni.sub.3 Ti precipitates as a second phase in the range below the
line AD (less than 45 at. % of (Ti+Zr)), while in the range above
the line BC (more than 53 at. % of (Ti+Zr)) a brittle and injurious
intermetallic compound NiTi.sub.2 precipitates as a second phase,
so that the plasticity inherent to NiTi and Ni-Ti alloys of
substantially the same composition as that of NiTi decreases and
hot and cold working becomes considerably difficult. In the range
below the line AB ((Ti+Zr) 45-53 at. %, the remainder (Ni+M) whose
atomic ratio is 99:1) the advantageous effect of substitution of a
part of Ni atoms by M decreases, while in the range above the line
CD ((Ti+Zr) 45-53 at. %, the remainder (Ni+M) whose atomic ration
is 50:50), the properties of NiTi deteriorate, thus considerably
decreasing the plasticity thereof and making the hot and cold
working difficult.
In the alloys according to the invention M for substituting a part
of the Ni atoms is Fe, Mo, Co and Cr. All these elements give the
above mentioned advantageous effects. Especially, Mo and Co give an
excellent corrosion resistance against H.sub.2 SO.sub.4. Co gives
the most excellent corrosion resistance against HDl, Cr gives the
most excellent wear resistance, followed by Mo, Co and Fe in the
order given. Fe is most effective in preventing transformation
caused by a temperature change or by working within the practical
temperature range, followed by Mo, Co and Cr in the order given.
For improvement of mechanical strength Mo is most effective. Thus,
through proper selection of Fe, Mo, Co, and Cr, it is possible to
obtain alloys having excellent properties, good for intended
purposes.
The reason why 0-10 at. % of Ti atoms of the alloys according to
the invention is substituted by Zr is that said substitution of the
Ti atoms by Zr renders it possible to further improve the
mechanical strength of the alloy according to the invention at room
temperature and high temperature and also the corrosion resistance
against HCl, although the substitution of 1-50 at. % of the Ni
atoms by M is capable of satisfactorily obtaining the object of the
invention without substituting a part of Ti atoms by Zr.
Substitution of a part of Ti atoms by Zr tends to decrease the
plasticity of the alloys according to the invention. If the rate of
substitution of Ti atoms by Zr is made larger than the atomic ratio
of 9:1, the plasticity of the alloys according to the invention
decreases, with the result that the hot and cold working cannot be
carried out.
As above mentioned, substitutions, according to the invention, of
1-50 at. % of the Ni atoms by M and of 0-10 at. % of the Ti atoms
by Zr in the alloy consisting of 45-53 at. % of Ti and the
remainder of Ni make it possible to prevent transformation caused
by temperature change or by working within the practical
temperature range, improve the mechanical strength at room
temperature and high temperature, and further improve the corrosion
and wear resistance of the alloys. In order to obtain alloys having
improved hot and cold workability, it is desirable to substitute by
M 1-25 at. % of the Ni atoms of alloys consisting of 47-52 at. % of
Ti and the remainder of Ni. It is more desirable to substitute by M
1-20 at. % of the Ni atoms of the alloys consisting of 48-52 at. %
of Ti and the remainder of Ni. In order to obtain alloys according
to the invention having excellent hot and cold workability and
mechanical strength, 0.1-7 at. % of the Ti atoms may be substituted
by Zr.
In order to obtain alloys according to the invention having
particularly excellent hot and cold workability 2-20 at. % of the
Ni atoms of alloys consisting of 49.5-50.5 at. % of Ti and the
remainder of Ni may be substituted by M. Moreover, in order to
obtain alloys according to the invention having excellent
mechanical strength and corrosion resistance, 1-20 at. % of the Ni
atoms of alloys consisting of 50.7-52.0 at. % of Ti and the
remainder of Ni may be substituted by M and 0.1-5 at. % of the Ti
atoms may be substituted by Zr. Furthermore, in order to obtain
alloys which will have improved mechanical strength when quenched
and tempered, 1-20 at. % of the Ni atoms of alloys consisting of
48-49 at. % of Ti and the remainder of Ni may be substituted by M.
Moreover, in order to obtain alloys which will have more improved
mechanical strength when quenched and tempered, 1-5 at. % of the Ni
atoms of alloys consisting of 48-48.6 at. % of Ti and the remainder
of Ni may be substituted by M.
As above mentioned, it is possible to obtain alloys having the
above mentioned properties by substituting by M a part of the Ni
atoms of NiTi and Ni-Ti alloys of substantially the same
composition as that of NiTi and further it is possible to obtain
alloys having an excellent corrosion resistance against
hydrochloric acid and sulfuric acid by using Mo or Co as M and
substituting a part of the Ti atoms by Zr. It is more desirable to
use a combination of Mo and Co as M. In order to obtain alloys
having particularly excellent wear resistance it is desirable to
use Cr or Mo as M. It is more desirable to use a combination of Mo
and Cr as M. In order to obtain alloys having an excellent cold
workability it is desirable to use Fe, Mo or Co as M. It is more
desirable to use a combination of Fe and Mo or of Mo and Co as M.
In order to obtain alloys having an excellent mechanical strength
at room temperature and high temperature, it is desirable to use Mo
or Cr as M and or substitute a part of the Ti atoms by Zr. It is
more desirable to use a combination of Mo and Cr as M and or
substitute a part of the Ti atoms by Zr. In order to obtain alloys
having excellent corrosion resistance and cold workability, it is
desirable to substitute a part of the Ni atoms by Fe, Mo and Co,
preferably at an atomic ratio of 1:1:1. In order to obtain alloys
having an excellent corrosion resistance and a more improved cold
workability, it is desirable to substitute a part of the Ni atoms
by Fe and Mo as M, preferably at an atomic ratio of 3:2. In order
to obtain alloys having the most excellent corrosion resistance and
cold workability, it is desirable to substitute a part of the Ni
atoms by Mo and Co as M, preferably at an atomic ratio of 2:3. In
order to obtain alloys having a particularly excellent wear
resistance, it is desirable to substitute a part of the Ni atoms by
Cr and Mo as M, preferably at an atomic ratio of 1:1. In order to
obtain alloys having the most excellent wear resistance, it is
desirable to substitute a part of the Ni atoms by Cr as M.
As above mentioned, the alloys according to the invention contain
Ni atoms part of which are substituted by M. If Fe and Cr which are
cheaper than Ni are used as M, the alloys according to the
invention are considerably less expensive.
The alloys according to the invention may contain as impurities
less than 0.1 percent by weight of Cu, less than 0.01 percent by
weight of P, less than 0.55 percent by weight of Mn, less than 0.6
percent by weight of C, less than 0.55 percent by weight of S, less
than 0.11 percent by weight of Si, less than 0.5 percent by weight
of Mg, less than 0.14 percent by weight of Al, less than 0.7
percent by weight of V, and less than 0.13 percent by weight of Tl
without giving much adverse effect on the properties of the alloys
according to the invention.
The alloys according to the invention may be melted by high
frequency heating process in a crucible made of graphite or carbon
under vacuum or in the atmosphere of inert gases such as argon,
helium, etc.
Heretofore, NiTi and Ni-Ti alloys of substantially the same
composition as that of NiTi have been melted by arc melting process
using consumable or non-consumable electrodes and subsequently
casted in a water cooled mold made of copper under vacuum or in the
inert gas atmosphere as in the case of general titanium alloys.
Such conventional method is complex in operation. According to this
method, the raw material is melted little by little locally be
electric arc and is not therefore thoroughly melted and blended, so
that such electric arc melting must be repeated several times to
obtain ingots of uniform composition. This makes melting and
casting costly. Moreover, if Mo having a high melting point is used
as M, it is impossible to melt it thoroughly and therefore Mo must
be used in the form of a mother alloy.
Under the above circumstances, the inventors have investigated on
various methods of melting and casting NiTi and Ni-Ti alloys of
substantially the same composition as that of NiTi and found out a
method which comprises substituting a part of the Ni atoms by M,
charging metal compositions into a graphite or carbon crucible in
close contact with one another, and melting said metal compositions
by a high frequency heating process at a temperature higher than
the melting point of alloys under the present invention but less
than 1,700.degree. C under vacuum or in the inert gas atmosphere,
thereby obtaining a uniform ingot without substantially any
reaction of the molten bath with the crucible.
A crucible made of oxides such as alumina, silica, magnesia, etc.,
other than graphite or carbon, causes the molten alloy to react
intensely with it. The melting requires a long time unless the
metal compositions are brought into close contact with one another
in the crucible, thus resulting in an increase of the carbon
content in the alloy. Moreover, if the temperature rises higher
than 1,700.degree. C, the molten alloy intensely reacts with the
crucible, with the resultant increase in carbon content in the
alloy.
The alloys according to the invention consisting of less than 50
at. % of (Ti+Zr) and the remainder of Ni, in which part of the Ni
atoms are substituted by M, have improved mechanical strength when
quenched and tempered.
That is, the alloys having the above mentioned compositions are
heated at a temperature of 700.degree.-1,000.degree. C and then
immediately quenched into water or oil and then tempered at a
temperature of 250.degree.-450.degree. C. In this way their
mechanical strength can be increased considerably.
Alloys quenched at a temperature less than 700.degree. C do not
show any sufficient hardening phenomenon, while alloys heated at a
temperature higher than 1,000.degree. C are excessively oxidized.
The tempering at a temperature less than 250.degree. C or higher
than 450.degree. C would not improve the mechanical strength. In
order to improve the mechanical strength by quenching and tempering
processes, it is desirable to substitute by M 1-20 at. % of the Ni
atoms of the alloys consisting of 48-49 at. % of Ti and the
remainder of Ni. It is most desirable to substitute by M 1-5 at. %
of the Ni atoms of the alloy consisting of 48-48.6 at. % of Ti and
the remainder of Ni.
The invention will now be described with reference to examples.
EXAMPLE 1
The alloys according to the invention having compositions shown in
the following Tables 1 and 2 were casted by heating and melting
them in graphite crucible at a temperature of about 1,410.degree. C
by a high frequency heating process under vacuum. These alloys were
formed into sheets, each having a thickness of 1.5 mm by hot
press-hammer-rolling processes at a temperature of
930.degree.-700.degree. C and the oxidized scales were removed by a
shot blast and then the thus treated sheets were pickled in an
aqueous solution of nitric acid-hydrofluoric acid. Then, the sheets
were immersed into various chemicals to determine the rate of
corrosion from the weight variation in a given time. The results
are shown in Tables 1 and 2. For comparison, NiTi and Ni-Ti alloys
of substantially the same composition as that of NiTi were casted
by arc melting process repeated five times in argon atmosphere by
the use of consumable electrodes, and the alloys thus obtained were
formed into sheets each having a thickness of 1.7 mm by hot
press-hammer-rolling processes at a temperature of 930.degree. to
700.degree.C and then the oxidized scales were removed by a shot
blast and the thus treated sheets were pickled in an aqueous
solution of nitric acid-hydrofluoric acid. The corrosion rate of
these sheets was determined and the results are also shown in
Tables 1 and 2.
Table 1 shows the corrosion rate of the sheets immersed in 5 wt%
and 10 wt% aqueous solutions of sulfuric acid at 100.degree. C for
24 hours and Table 2 shows the corrosion rate of the sheets
immersed in 3 wt% and 5 wt% aqueous solutions of hydrochloric acid
at 100.degree. C for 24 hours. ##SPC1## ##SPC2##
As seen from Table 1, against the aqueous solutions of sulfuric
acid, the alloys in which nickel atoms are partially substituted by
M and those in which nickel atoms are partially substituted by M
and further titanium atoms are partially substituted by zirconium,
have considerably improved corrosion resistance and of them, the
alloys, in which nickel atoms are partially substituted by Mo or
Co, are excellent in corrosion resistance, and particularly the
alloys, in which nickel atoms are partially substituted by both of
Mo and Co, have the highest corrosion resistance.
As regards the relation between the rate of substitution and its
effect on improvement of corrosion resistance, Mo is fairly
effective in improving the corrosion resistance even when used at a
substitution rate of as low as 0.3 at. % (atomic ratio of Ni and Mo
is 99.7:0.3) and the effect increases until the substitution rate
reaches about 8 at. %, but beyond such a rate, the effect becomes
constant. In the case of cobalt, the area developing the effect
lies in a higher side of the rate of substitution than that of
molybdenum.
Furthermore, as seen from Table 2, against the aqueous solutions of
hydro-chloric acid, the alloys in which Ni atoms are partially
substituted by M and those in which Ni atoms are partially
substituted by M and further titanium atoms are partially
substituted by zirconium, have considerably improved corrosion
resistance. Among M, cobalt or a combination of Co and Mo is the
most effective.
As regards the relation between the rate of substitution and its
effect on improvement of corrosion resistance, in the case of
cobalt, the effect appears when the rate of substitution is about
0.4 at. % (atomic ratio of Ni to Co being 99.6:0.4) and increases
until the rate reaches about 10 at. %, but beyond such a rate, the
effect remains constant. Furthermore, in case titanium atoms are
partially substituted by Zr the effect appears when the rate of
substitution is about 1.0 at. % (atomic ratio of Ti to Zr being
99:1) and increases until the rate reaches about 5 at. %; but,
beyond such a rate, the effect remains substantially constant.
EXAMPLE 2
Sheets, 1.5 mm thick, made of the alloys according to the invention
in the same manner as described in Example 1 and sheets of the same
thickness made of conventional alloys the compositions of both
alloys being shown in Table 3, were polished with an emery paper
and then buffed and thereafter subjected to abrasion test by
Ohgoshi's rapid abrasion tester which will be described below, to
determine the coefficient of wear and the thus obtained results are
shown in Table 3.
The above mentioned test was effected as follows:
The above described sheet was set in parallel with the axis of a
friction disc having a diameter of about 30 mm and a thickness of
about 3 mm and the friction disc was pressed against the surface of
the above described sheet under various pressures and rotated at
various speeds at fixed points on the sheet until it covers a given
running distance (circumference of the disc X number of rotations)
and the width of the scratch marks were measured and the
coefficient of wear (Ws) was calculated according to the following
formula
Ws = Bv.sub.0.sup.3 /8rP.sub.0 l.sub.0
Ws = Coefficient wear
B = 3.05
b.sub.0 = Width of scratch mark
r = Radius of the friction disc
P.sub.0 = Pressure of applying disc against the sample sheet
l.sub.0 = Running distance
In this example, r was 30 mm, P.sub.0, 6.5 Kg; and l.sub.0, 200 m.
##SPC3##
As seen from Table 3, the wear resistance is not considerably
influenced by the atomic ratio of (Ni+M) and (Ti+Cr) and as the
rate of substitution of M and Zr increases, the rate of increase in
wear along with increase in rotating speed of the disc is reduced.
Furthermore, the influence of each substituting element is most
remarkable in Cr and the effect decreases in the order of Mo, Co,
Fe and Zr and the best result is obtained in the use of a
combination of Cr and Mo. Irrespective of the kind of element used
for substitution, the wear resistance of alloys is scarcely
improved in the field of "oxidated wear" (wearing in which worn
metal surface is covered with metallic oxide and the coefficient of
wear is very low, irrespective of the rotating speed) where the
rotating speed of the disc is low, at whatever rate of the
substituting elements may be used. But, in the field of
"bright-surface wear" (wearing in which worn metal surface is
bright and the coefficient of wear sharply increases as rotating
speed increases) where the rotating speed is high, improvement of
wear resistance is seen when the rate of substitution is about 0.5
at. %. The coefficient of wear decreases according to increase in
the rate of substitution up to 30 at. %.
Further, in this test, as the rotating speed increases, the
temperature on the wearing surface rises and hence the above
described test result shows that the temperature at which the
oxidated wear changes to the bright-surface wear shifts to the
higher temperature side by partial substitution of Ni atom by M and
Ti atom by Zr.
EXAMPLE 3
Sheets, about 5 mm thick, made of the alloys according to the
invention in the same manner as that described in the Example 1 and
sheets of the same thickness made of conventional alloys, the
compositions of both alloys being as shown in Table 4 and
manufactured were finally tempered in argon atmosphere at
930.degree. C for 1 hour and then cooled to room temperature at a
cooling rate of about 50.degree. C in every hour. Measurement was
taken of the hardness at room temperature and a high temperature of
700.degree. C, the hardness at room temperature after the quenching
and tempering processes (tempering at 350.degree. C for 1 hour
after quenching in water from 930.degree. C), the temperature at
which the transformation occurs (hereinafter expressed as "Ms") and
the maximum temperature beyond which the transformation is no
longer caused by working (Md) (hereinafter expressed as "Md"). The
results are shown in Table 4.
Ms in Table 4 was determined by sound when the sample sheet was
struck by hammer, because conventional NiTi and Ni-Ti alloys of
substantially the same composition as that of NiTi vary
discontinuously and remarkably in the vibration damping property
above and below the transformation temperature and when the alloys
are struck at a temperature higher than the transformation
temperature, a metallic sound is given out, while is struck at a
temperature lower than said transformation temperature, the alloys
make a non-metallic dull sound.
Md in Table 4 was defined as follows:
If the alloy sheet once deformed at a temperature lower than Md
returns to its original shape when heated to a temperature higher
than a specific temperature. In consideration of such property, Md
is defined as the maximum bending temperature above which the bent
sheet cannot return to its original form when heated at 500.degree.
C. ##SPC4##
As seen from Table 4, the alloys according to the invention in
which Ni atoms are partially substituted by M and Ti atoms by
zirconium are extremely lower in Ms and Md than the conventional
alloys.
The effect of decreasing Ms and Md is most remarkable in Fe among M
and the effect reduces in the order of Mo, Co and Cr.
The hardness in the annealed state and the hardness at high
temperature of the alloys, wherein Ni atoms are partially
substituted by M and Ti atoms by zirconium, are improved highly and
as to the substituted element, Mo has the most remarkable effect
and Zr and Cr follow Mo, and Co have relatively low effect. The
highest effect can be attained by a combination of Mo, Cr and
Zr.
Substitution of Ni atoms by one or more of Fe, Co and Cr as M shows
a remarkable age-hardening effect by quenching and tempering
treatments when (Ti+Zr) atoms are less than 50 at. %. Such an
effect is most remarkable when the substitution is effected by
Fe.
FIG. 2 shows a relation between tempering temperature and the
hardness after tempering of the alloys, wherein Ni atoms are
partially substituted by Fe, at different rates of
substitution.
As seen from FIG. 2 the alloy having a higher rate of substitution
is larger in the hardness increase owing to the tempering, and the
peak of tempering hardness shifts somewhat to the higher
temperature side.
EXAMPLE 4
The alloys according to the invention manufactured by the method
similar to that described in Example 1 and the conventional alloys
were formed into sheets each having a thickness of 2 mm. The sheets
thus obtained were finally annealed at 93.degree. C in argon
atmosphere for one hour.
Then, these sheets were cooled at a cooling rate of about
50.degree. C/min to room temperature and then subjected to cold
rolling. The maximum rate of rolling beyond which further rolling
is impossible owing to crack formation was measured and the results
thus obtained are shown in Table 5. ##SPC5##
As can be seen from Table 5, the alloy according to the invention
in which a part of the Ni atom content are substituted by M can
have improved plasticity at about room temperature.
Heretofore, in order to improve the mechanical properties of NiTi
and Ni-Ti alloys substantially the same composition as that of
NiTi, addition of the third and the fourth elements thereto has
been tried. But, in both cases the plasticity of the alloy becomes
decreased, with the result that the hot and cold working processes
become difficult thus resulting in difficulty in the practical use
of the alloy. The invention provides a method of substitution by,
instead of addition of, the above mentioned elements and hence can
improve the mechanical properties of the alloy without decreasing
its plasticity.
With regard to the effect of the elements for substituting a part
of the Ni atoms of the alloy according to the invention, Co and Fe
are most effective while Mo is less effective and Cr is the least
effective. Use of more than one of such elements is also effective.
Particularly, the combinations of Co and Mo and the Fe and Mo are
considerably effective.
EXAMPLE 5
An alloy according to the invention, in which 5 at. % of Ni atoms
of NiTi were substituted by Mo and 5 at. % of the Ti atoms were
substituted by Zr, was melted in a crucible made of graphite by a
high frequency heating process under vacuum.
The molten alloy thus obtained was maintained at various
temperatures for 20 minutes and then cast into a water cooled mold
made of copper. The carbon contents of the ingots thus obtained
were investigated and the results obtained are shown in Table
6.
Ni, Ti, Fe, Mo and Zr were so charged into the crucible that these
elements become laminated therein so as to easily react each other.
---------------------------------------------------------------------------
Table 6
Melting Melting temperature C (%) temperature C (%) (.degree.C)
(.degree.C)
__________________________________________________________________________
1,280 0.04 1,500 0.08 1,320 0.05 1,550 0.10 1,360 0.05 1,600 0.13
1,410 0.06 1,650 0.19 1,450 0.08
__________________________________________________________________________
as seen from Table 6, the alloys according to the invention do not
react with the crucible when the temperature is less than
1,700.degree. C so that the molten alloy is not contaminated with
graphite. The alloys can therefore be used in practice.
The segregation of the alloy compositions of the ingots cast by the
above mentioned method was measured and the results are shown in
Table 7.
In this case, the temperature of the molten bath was 1,410.degree.
C. The results obtained by measuring the segregation of the alloys
melted by the conventional arc melting process are also shown in
Table 7 for the comparison. ##SPC6##
As seen from Table 7, the alloy according to the invention can be
melted and cast in the crucible made of graphite by means of the
high frequency heating under vacuum. This casting process, given
only once, provides an ingot having less segregation and carbon
contamination.
The description and examples given above are intended to illustrate
the best mode of performing the invention. It is apparent that many
modifications thereof may occur to those skilled in the art, which
will fall within the scope of the following claims.
* * * * *