US3174851A - Nickel-base alloys - Google Patents

Description

United States Patent 3,174,851 NICKEL-BASE ALLOYS William J. Buehler, Hyattsville, and Raymond C. Wiley,

Rockville, Md., assignors to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Dec. 1, 1961, Ser. No. 157,049

3 Claims. (Cl. 75-170) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a series of novel structural alloys of the intermetallic compound type which are characterized by unusual mechanical and physical properties.

Most intermetallic compounds, other than TiNi, are very brittle, lack any form of ductility at room temperature and in spite of many other outstandingly good properties displayed by these compounds, such as strength maintenance at high temperatures, their brittleness at room temperature has made these compounds virtually useless in structural applications except as minor strengthening constituents in a more ductile matrix metal or alloy.

Novel intermetallic compound base materials of the TiNi type have now been discovered which not only possess the desirable properties characteristic of intermetallic compounds in general but also possess hitherto unknown and unusual properties.

Accordingly, it is an object of the present invention to provide a new series of structural alloys of the intermetallic compound type characterized by high strength at room temperature and at elevated temperatures, good oxidation resistance up to a moderate fraction of the melting temperature, good corrosion resistance, moderate density, reasonable ductility and impact resistance at all temperatures, and good weldability and being further characterized by non'magnetic stability at useful temperatures and unusual mechanical vibration damping properties which are sensitive to both composition and temperature changes.

It is a further object to provide intermetallic compoundbase alloys capable of being readily melted, cast into a chemically homogeneous solid mass and worked hot (above recrystallizationtemperature), cold (below recrystallization temperature) or by hot and cold means to a final usable shape.

It is yet another object to provide novel intermetallic compound alloys capable of heat treatment to any required hardness value from approximately about 65 R to approximately about 62 R It is a still further object to provide a non-magnetic alloy capable of being heat treated or developed to high hardness and strength for use in non-magnetic tools and other functions in connection with magnetic sensitive devices.

The term intermetallic compounds as a general term is considered hereinafter as an intermediate phase in an alloy system, having a reasonable range of homogeneity and relatively simple stoichiometric proportions, in which the nature of the atomic binding can vary from metallic to ionic, and further includes all intermediate phases in binary and higher order metal systems whether ordered or disordered. These intermetallic compounds are combinations of two or more metals, the atoms of such metals generally being in a simple whole number ratio. In the majority of cases, however, the formulas of intermetallic compounds do not agree with formulas based on the principle of valency.

The novel alloys developed in accordance with the present invention occur in three possible phases as illustrated by the following equilibrium equation:

TiNi=Ti Ni+TiNi They were prepared as illustrated in the following detailed example.

EXAMPLE The raw materials used were Mond nickel shot and commercially pure titanium bar stock.

The preparation of the novel intermetallic TiNi alloys may be divided into three distinct steps as follows:

(a) Melting of the alloy (b) Working of the arc-cast alloys (c) Heat treating the wrought materials Melting of the alloys The alloys, due to their high titanium content, may be melted by either consumable or non-consumable are methods or the like employing a Water-cooled copper crucible or hearth.

Working of the arc-cast alloys All of the cast alloys between about 52 to 56 weight percent nickel and correspondingly between about 48 to 44 Weight percent titanium may be hot worked without any preliminary heat treatment. A stoichiometric TiNi composition of 55.1 weight percent nickel and 44.9 weight percent titanium was readily hot worked in the as cast condition between about 650 C. to about 1100 C., the preferred hot working temperature range being from about 700 C. to 900 C.

Alloys containing above 56 weight percent nickel, that is from about 56 to 64 weight percent nickel required a preliminary heat treatment to render them hot workable. This heat treatment consisted of heating the alloys to about 1050 C. until heated through and then slowly cooling to room temperature. Alternatively, the alloys may be heated to about 1050 C. until heated through, cooled slowly to about 850 C. and held at that temperature until heated through and subsequently allowed to slowly cool to room temperature. The principle behind the above pre-working heat treatments is to precipitate and coalesce the excess compound phase TiNi3 from solution with the compound phase of TiNi. This results in a ductile TiNi matrix interspersed with the more brittle TiNi compound coalesced into harmless particles. Following the above described alternative pre-working heat treatments the two phase TiNi-l-excess TiNi alloy was capable of being rolled at any temperature between about 700 C. to about 900 C.

35 Heat treating the wrought materials The hardness of alloys containing between about 52 to 56 weight percent nickel (remainder titanium) and being predominantly single phase TiNi was only very slightly affected by any heat treatment regardless of the rate of cooling.

Conversely, the hardness of alloys containing between about 56 to 64 weight percent nickel (remainder titanium) are very much affected by heat treatment and particularly by the cooling rate. These alloys when heated to above about 900 C. and quenched in room temperature water .attain a high hardness. For instance, an alloy of about 60 weight percent nickel and about 40 weight percent titanium yielded, when quenched from between 900 C. and 1110 C., a hardness varying between 58 R and 62 R as may be seen from Table I.

Table 1 AVERAGE HARDNESS OF 60 Ni-40 Ti (WEIGHT PER- CENT) ALLOY WATER QUENCHED FROM DIFFERENT TEMPERATURES Quenching Temp, C. Harilincss, Remarks 1,110" O 62 Heat treated in an air atmosphere. 1,000 C V 01 Do. 900 C 58 Do.

The same 60 Ni-40 Ti (wt. percent) alloy when furnace cooled (average cooling rate about 50" C./hr.) attained a final hardness of about 35 R such hardness being approximately equal to the hardness of alloy compositions being in the T iNi phase (52 to 56 weight percent nickel) as shown in Table II.

The above data clearly show the capability of the nonstoichiometric TiNi alloys (i.e., those containing excess nickel) to be hardened by quenching. It is also clear that an alloy of 56 wt. percent Ni (remainder Ti) is the transition between hardenable and non-hardenable alloys and that a great excess of the hardening constituent TiNi (above about 64 Wt. percent nickel) serves to reduce the quenched hardness. Thus the preferred range, for maximum hardness, would be between 58 and 62 wt. percent Ni.

The hardness of quench-hardened alloy (56 to 64 wt. percent Ni, remainder Ti) components may be reduced to a lesser degree of hardness if such is required for a specific application. Such reduction must be based upon the best compromise of mechanical properties for the particular application. Reduction of hardness of quenchhardened all-oys may be accomplished by (A) slowing down the cooling rate of the heat treated component to yield hardnesses between about 35 R (furnace cool) and about 62 R (water quench) and by (B) tempering. This tempering process is accomplished by reheating the quench-hardened alloy to various temperatures below the point of change in slope of the phase boundary between the TiNi and TiNi-i-TiNi phase areas (about 900 C.) and cooling at a specified slow rate, the final tempered hardness being determined by the heating temperature, period of time at the heating temperature and the rate of cooling. In order to minimize surface oxidation (when heating above about 600 C.) the above hardening and tempering heat treatments may be performed in a controlled atmosphere of helium or argon. In many applications, however, heat treatment in air will sufiice.

Further hardness data for TiNi, Ti Ni and TiNi compositions are shown in Table III.

Table III Alloy Alloy Melting Hot Roll Temp, C Hardness, Composition R TiN i Non-consu1nable 30-31 TiNi TiNi TiNi 'liNL As cast (No H.R.)..

From the above data it may be seen that the room temperature hardness increases with an increase in rolling temperature which is undoubtedly related to the higher temperature of heatingand fairly rapid cooling rate from temperature. It may also be seen that while the Ti Ni composition alloy is quite hard (53 R the TiNi compound has a hardness (34 R more like that of the TiNi alloy. Yet in spite of the much lower hardnessexhibited by TiNi it is similar to the Ti Ni compound in that it is brittle even at high homologous temperatures.

A particularly unusual property was observed of these novel alloys containing from about 50 to 70 wt. percent Ni (remainder Ti) and this was the property of these alloys to retain their hardness characteristics independent of temperature, for example, at temperatures ranging from about room temperature up to about 463 C. and down to about C. Alloys characterizedby an essentially pure TiNi phase (54.5 to 55.1 W/o Ni-Ti have even shown a tendency to exhibit a secondary hardening. This is indicated in Table III, column 8 Tensile properties were measured on both 54.5 and 55.1 wt. percent Ni alloys (remainder Ti). In every case, a standard specimen measuring 0.252 diameter x 1.0" gage length was employed. The test sections were finish lapped in the longitudinal direction to avoid any possible transverse notches. To avoid oxidation of the prepared sample surfaces and minimize the possible interstitial element (0, N, H) pickup, vacuum or controlled atmosphere heat treating was used. Vacuum heat'treating was performed in an evacuated quartz tube. The tensile test results obtained from the two TiNi alloys are shown in Table IV.

Table IV TENSILE TEST DATA 54.5 w/o N i-Ti Alloy (room temperature) Ultimate Yield Elonga- Reduction Modulus of Specimen Treatment Tensile Str., Strength b tion, in area, Elasticity, Remarks s linfl lbs/in. percent percent p.s.i.

800 C. 1 hour furnace cooled e 112, 100 40, 000 8. 1 11. 6X10 Bgoke gutside gage en t 800 C. 1 hour water quench e 123,800 40, 700 15. 16.0 11. 8X10" g 54.5 w/o Ni-Ti Alloy (185 to 192 F. test temperature 800 C. 1 hour furnace cooled e 110,500 46, 800 3. 6 11. 1X10 Biioke olutside gage engt 800 C. 1 hour water quench e 115, 300 55,100 10. 9 13.0 11. 2X10 55.1 W/O Ni-Ti Alloy (room temperature) Hot swaged at 900 0., air cooled 125, 000 81, 400 8.1 1,000 C. min., furnace cooled 116, 700 56, 200 7. 2 Hard-:26 R

Do .1 114, 200 33, 600 3. 2 Broke outside gage lRength. Hard=24 Des 140, 500 as, 200 9.9 Hard =24 3.. 1,000 C. 30 min, water quench 82, 320 71, 400 3. 5 Hard=33 Rt.

Do. 84, 400 62, 250 4. 5 l1. 8X10. Hard=31 Be.

* Tensile specimen size 0.252 dia. x 1.000 gage length.

b Offset- 0.2%.

e Heat treatment performed in an argon atmosphere.

6 Specimen sealed in an evacuated quartz tube during heat treatment.

Upon observation of the above data it becomes appar- Table VI ent that the ductility, as indicated by the percentage 30 elongated, can go as big has 15.5% with the average being in the 7-10 range. For an intermetallic compound this is an unusually and unexpectedly high room temperature elongation. Moreover, it is seen that the yield CORROSION CHARACTERISTICS Corrosive media: Resultant attack Salt spray, 20% soln.,

95 F. for 96 hrs. Faint whitish surface destrength varies considerably with composition and heat 35 treatment while the ultimate tensile strength and modulus posit on b k edge, f of elasticity are fairly constant regardless of composition specimm NO attack on and heat treatment. 6X osed surface For determination of impact properties, carefully p prepared unnotched square cross-section bars were used. 4 Sea Water 192 The specimen surfaces were hand lapped in the longitudi- Normal air atmosnal direction to minimize transverse scratches. The phepe Nil. Charpy impact tests were performed in a standard Riehle Normal handhn N11. machine. The resulting data are summanzed in Table V. g

Table V IMPACT DATA FOR TiNi COMPOSITION ALLOYS 1 GIVEN PRIOR THERMAL TREATMENTS AND AT VARIOUS TEST TEMPERATURES Nominal Alloy Specimen Section Conditions of Test Charpy Composition Size Impact ft.lbs.

54.5 w/o Ni-Ti 2 0.296 x 0.296 Test Temperature: 75 F. (R.T.) 28 54.5 w/o Ni-Ti 0.296 x 0.296 Test Temperature: 125 F 32 54.5 w/o Ni-Ti 0.296 x 0.296. Test Temperature: 200 F- 29. 5 54.5 w/o Ni-Ti 0.296 x 0.296. Test Temperature: 112 F 40 54.5 w/o Ni-Ti 2 0.206" x 0.206 Cooled to l12 F., Warmed in RT. water, 23

stabilized 15 min. in R.T. air. 54.5 w/o Ni-Ti 2 0.296 x 0.296 Cooled to 112 F., Warmed in RT. water, 25

stabilized 15 min. in RT. air, plus heat to a test temperature of 160 F. 55.1 w/o Ni-Ti 3 0.297 x 0.297" Test Temperature: F. (R.T.) 24 55.1 w/o NiTi 0.297 x 0.297 Test Temperature: 200 F 8 55.1 w/o Ni-Ti 3 0.207 x 0.297 Test Temperature: -l12 F- 43 1 Unnotched square cross-section bars were employed. 2 Specimens prepared from hot swaged (0000 0.) bars. 3 Specimens prepared from hot rolled (900 0.) plate. Again, as in the case of the tensile elongation, un- Table VII usually high impact strengths were attained as compared OXIDATION orrannc'rnnrs'rros with most intermetallic compounds. For both of the TiNi alloys the minimum value was 23 ft.-lbs. even on the undersize specimens. Especially to be noted is the Weight Gain (Grns.) due to Oxidation of Various Temperatures Testing Time, Hrs.

increase in impact strength at temperatures well below 800C, 1 0()[)(] freezing.

Specimens of a 55.1wt. percent Ni (remainder Ti) alloy .016 .007 were exposed to various common corrosive media and 1853 to elevated temperature oxidation attack. The results of 3 these tests are summarized, respectively, in following 1 5 I Tables VI and VII.

It will be noted from Table VI that in each case the attack was negligible and only in the rather drastic salt spray tests was a perceptible film formed where the specimen was held. The passivity of this alloy to corrosive attack is obviously a highly desirable characteristic.

From Table VII it will be seen that at 600 C. there was very little initial oxidation and oxide buildup was almost negligible after the first two hours. At 800 C. oxidation proceeded steadily after the first two hours and at 1000" oxidation was initially rapid and proceeded steadily. At 800 C. and 1000 C. spalling of the oxide surface was moderate to heavy.

In the fabrication of present day structural materials joining is an extremely important consideration. To obtain an indication of the Weldability of the TiNi material, two chamfered A5" thick hot rolled plates of TiNi were butt welded together by the heliarc method. Little ditliculty was encountered in making the joint and the weld section appeared to be free of cracks and porosity. Based upon the observed properties in this arc-cast TiNi material, the weld section should be quite strong and tough. Further, examination of the magnetic properties of the weld section indicate that it is equally as paramagnetic as the base material.

Among the various unusual properties exhibited by these novel alloys, the property of paramagnetism is of utmost importance. A paramagnetic material has been defined as a material whose specific permeability is greater than unity and is practically independent of the magnetizing force. The nickel-titanium alloys in the composition range which covers Ti Ni, TiNi, and TiNi are highly paramagnetic, in spite of the high amount of nickel present in there alloys. Alloys of the 54 to 60 w/o Ni, remainder Ti composition have been magnetically evaluated after various thermal treatments and at widely varying temperature. The magnetic testing included both magnetic susceptibility and permeability measurements. In these tests it was found that the permeability approached extremely close to unity regardless of the temperature, residual stresses, or prior thermal treatment. Care must be exercised to remove any oxide coating in cases where the TiNi-base alloys are to be used in non-magnetic applications. This is caused by the combination of some Ni of the base alloy with O to form a ferromagnetic oxide coating.

Of considerable importance in regard to these novel alloys is the unusual characteristics exhibited by the mechanical vibration damping eifect. The stoichiometric alloy in both the arc-cast and hot worked conditions exhibits a unique and drastic change in vibration damping with minor changes in temperature and composition. Quantitative and qualitative experiments have shown the damping of a 54.5 w/o Ni-Ti alloy With minor amounts of Fe (about 0.1 w/o) to change from a highly damping material at room temperature (25 C.) to-a very low vibration damping material at 54 C. and above. Internal friction experiments performed on 0.036 diameter wire showed the logarithm of amplitude to decrease from 2.3 to 1.1 in 35 cycles at room temperature (25 C.) while the same wire drops from 2.3 to 2.1 in 35 cycles when heated at 93 C. This illustrates clearly the damping change in wrought wire of the 54.5 W/o Ni, approximately 0.1 w/o Fe, remainder essentially Ti. Even more'drastic changes in damping behavior are exhibited by this composition alloy when in the arc-cast condition. These changes in damping appear to be associated with the phase equilibria of the alloy system. As the temperature is raised the TiNi phase increases in quantity at the expense of reducing the extraneous phases present (Ti Ni and TiNi As this occurs damping is markedly 'decreased.

The phase equilibria theory is further confirmed by the fact that alloys containing excess Ni or excess Ti over the stoichiometric composition have distinctly different room temperature damping properties. For example the Tib cs rich alloys (less than 54.5 w/o Ni) are highly damping at room temperature, while alloys on the Ni-rich side (in excess of 54.5 w/o Ni) show low damping at room temperature, thus indicating that the Ti Ni phase coupled with the liNi produces the high damping capacity. Anything lessening the Ti Ni phase, e.g. increased Ni, higher temperatures, impurity atoms like Fe, etc. causes minor changes in the TiNi/Ti Ni phase equilibria and thus promotes drastic vibrational damping changes- This unusual damping phenomenon may lead to the utilization of these alloys as temperature sensing devices.

A summary of the properties of the novel TiNi base alloys is presented in Table VH1. (See column 8.)

In summary, novel TiNi alloys containing from about 50-70 wt. percent Ni (remainder Ti) have been discovered which possess the unusual combination of properties of high hardness at wide temperature variations and especially at temperatures Well below freezing and having unusually good ductility. and impact strength at these same temperatures. Within this range of 50-70 wt. percent Ni, the alloys may be subdivided into those alloys having a range of about 52 to about 56 wt. percent Ni (remainder Ti) and those alloys containing from about 56 to about 64 wt. percent Ni (remainder Ti). The former are characterized by the existence of an almost wholly TiNi phase, by being readily workable whether hot or at room temperature and by exhibition of unusually high ductility at room temperature. The latter alloys are characterized by being two-phase materials (TiNi-I-TiNig) capable of being hardened to'high hardness levels. The combination of the high hardness of these latter alloys and their characteristic paramagnetism (magnetic permeability=less than 1.02) is of great importance and leads to their use as superior non-magnetic tools magnetometer applications and structural materials which will remain stably nonmagnetic, free of corrosive attack, and resistant to abrasion.

Table VIII SUMMARY OF PROPERTIES OF TiNi PHASE ALLOYS [Physical (55.1 w/o Ni-Ti)] Density (25 C.), gr./cm. 6.45.

Melting point, C. 1240-1310. Melting point, F. 2264-2390. Crystal structure CsCl (B.C.C.). Lattice parameter, A 3.015.

Electrical resistivity (25 C.), microhm- Electrical resistivity (900 C.), mi-

crohm-cm. -132.

Linear coef. of expansion (24-900 C.),

per C. 10.4 10- Recrystallization temperature, C. 550-650. Magnetic permeability l.002.

Magnetic susceptibility (mass, -196 to 550 C.) 5-9 10' [Mechanical] 54.5 w/o Ni V 55.1 w/o Ni Ultimate Tensile Stn, p.s.i-..- 110,000-124,000- 82,000-140,000.

Yield Str., p.s.i** 40,G00-55,000 33,00081,400.

Youngs Modulus, p.s.i 11.2-11.8 X 10 Up to 11.8 X 10 Tensile Elongation, Up to 15.5- Up to 10.

percent? Reduction in Area, psrcent-... Up to 1G Hardness. Rockwell-A 42-52 65-68.

Hot Hardness," D.P.H.:

Impact Str., ft.-lbs.:

24 0. (room temp.) C Modulus of Rupture, p.s.i.. Mod. of Elas. (Trans. Bend),

p.s.i.

25 0 (room temp.) 0 (3....

*Specimeus rapidly cooled prior to testing. Percent ollset=0 2%. Gage 1ength=1 1H.

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the novel alloys of the invention and that modifications or alterations may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent of the United States of America is:

1.A novel alloy composition consisting essentially of from about 50 percent to about 70 percent nickel by weight and correspondingly from about 50 percent to about 30 percent titanium by weight, said alloy having the structure of a TiNi phase in combination with a TiNi pha-se dispersed in a TiNi matrix within a temperature range of from about 500 C. to about -75 C. and having the properties of being paramagnetic, of retaining hardness throughout said temperature range and of being corrosion resistant.

2.A novel alloy composition consisting essentially of from 52 percent to about 5 6 percent nickel by weight and correspondingly from about 48 percent to about 44 percent titanium by weight, said alloy having the structure of a substantially TiNi phase within a temperature range of from about 500 C. to about 75 C. and having the properties of being paramagnetic, of being highly vibration damping at about room temperature and having the capability of being plastically deformed at about room 1t) temperature and retaining the deformed shape until heated to a higher temperature whereupon the prior nondeformed condition will be reassumed.

3. A novel alloy composition consisting essentially of from about 56 percent to about 64 percent nickel by weight and correspondingly from about 44 percent to about 36 percent titanium by weight, said alloy having the structure of a substantially TiNi phase dispersed in a TiNi matrix within a temperature range of from about 450 C. to about 75 C. and having the properties of being paramagnetic, of high hardness upon heat treatment, of being abrasion and corrosion resistant and capable of being hot wrought into useable shapes prior to hardening.

References Cited by the Examiner I. J. Wallbaurn, Archiv. Fiir Das Eisenhuttenwesen, JG 14, 1940-1941, pages 521-526.

Hansen: Constitution of Binary Alloys, published by McGraw-Hill Book Co., Inc., New York, 1958, pages 1049-1053.

Poole et al.: The Equilibrium Diagram of The System Nickel-Titanium, Journal of the Institute of Metals, vol. 83, pages 473-480, July 1955.

DAVID RECK, Primary Examiner.

RAY K. WINDHAM, WINSTON A. DOUGLAS,

Examiners.

Claims (1)

1. A NOVEL ALLOY COMPOSITION CONSISTING ESSENTAILLY OF FROM ABOUT 50 PERCENT TO ABOUT 70 PERCENT NICKEL BY WEIGHT AND CORRESPONDINGLY FROM ABOUT 50 PERCENT TO ABOUT 30 PERCENT ITANIUM BY WEIGHT, SAID ALLOY HAVING THE STRUCTURE OF A TINI PHASE IN COMBINATION WITH A TINI3 PHASE DISPERSED INA TINI MATRIX WITHIN A TEMPERATURE RANGE OF FROM ABOUT 500*C. TO ABOUT -75*C. AND HAVING THE PROPERTIES OF BEING PARAMAGNETIC, OF RETAINING HARDNESS THROUGHOUT SAID TEMPERATURE RANGE AND OF BEING CORROSION RESISTANT.