US2048166A - Copper-nickel-titanium alloys - Google Patents

Description

Patented July 21, 1936 ires STATES PATENT OFFICE COPPER-NICKEL-TITANIIM ALLOYS N. Y., a corporation of Delaware No Drawing. Application October 1, 1931, Serial No. 566,311. Renewed December 17, 1935 9 Claims. (Cl. 148-32) This invention relates to improved coppernickel-titanium alloys of the solid solution type.

Hitherto it has been proposed to utilize the metal titanium as a deoxidizing agent for alloy steels and the like in which the residual content of titanium contemplated was very small, usually less than .1 percent. It has been further proposed to use titanium as a toughening agent or Brain refiner in which cases the alloy may have some 1 percent of titanium retained, although several disclosures specify ranges of titanium for such purposesup to 10 percent. It is an object of the present invention to provide improved hardenable nickel alloys by combining with a suitable alloy, referred to as the base alloy, quantitles of titanium and titanium-like elements.

It is'a further object of this invention to confer hardening properties upon particular base alloy compositions chosen to provide other desirable properties, whereby not only the hardness but the elastic strength and breaking strength of the base alloy is increased without materially changing its other characteristic properties.

It is a still further object of this invention to alloy a suitable hardening agent with a nickelbearing base material and subject the resulting alloy to a particular heat treatment to develop and control increased strength properties. These and other desirable advantages of the present invention will be set forth and described in the accompanying specification, certain preferred compositions being given by way of example only, for, since the underlying principles may be applied to other specific compositions, it is not intended to be limited to those herein shown except as such limitations are clearly imposed by the appended claims.

The present invention comprehends a wide variety of base alloy compositions and three preferred hardening agents, as will be described more in detail hereinafter. The preferred base alloy which is particularly amenable to the proposed treatment may be defined as nickel-bearing solid solutions having the face-centered cubic lattice type of crystalline structure. The claim for this broad definition is predicated on experimental work with six distinct alloy series of this type in addition to the metal nickel, all of which behave substantially similarly, and which behavior will be described more in detail below. No exceptions to this definition have yet been encountered, although the degree of hardening displayed by different combinations of base alloy and hardening 5 agent, of course, vary somewhat in degree. In one such series, viz., iron-nickel-chromium-titanium, the hardening characteristics were displayed in alloys having ranges of nickel content varying from substantially 6 to 96 percent. 10 The preferred hardening agents comprehended within the spirit and scope of this invention are titanium, aluminum, and zirconium, and it is apparent that the hardening characteristics herein disclosed may be properties or functions of the 15 boron and the titanium groups of the periodic classification of the elments according to Mendeleeff. Of these hardening agents titanium has been found to be the more useful from the standpoint of developing physical properties of engl- 20 neerlng value combined with practical working qualities. For the purposes of illustration, in order to more clearly set i'orthv the novel features of the present invention, the characteristics of iron-nickel base 5 alloys alloyed with titanium as a hardening agent will be discussed. Nickel-iron alloys which include from about 25 percent to substantially 100 percent nickel in their composition are soft and relatively unaffected in hardness by heat treat- 30 ment. Titanium is soluble in these alloys and, if completely dissolved therein, the resulting ternary alloys retain substantially the original soft character. If asuilicient amount of titanium be added, 35 however, the resulting alloys are soft only when cooled rather rapidly from a high temperature; if reheated to some lower temperature range, or allowed to cool rather slowly through this range, a substantial rise in hardness occurs. A still further 40 increase in titanium content causes the alloys to become increasingly hard, even when subjected to rapid cooling from high temperatures. yet these alloys change somewhat in hardness with heat treatment. These characteristics in a series of iron-nickel alloys containing 35 percent nickel and varying amounts of titanium are shown in the following table:

Number 1 v 2 a 4 5 e 7 50 Percent titanium 0 .49 L31 220 3. 13 4.00 6.71 B n 1ooo 0., air cool 132 1a! 131 151 178 268 39.3 {100 mam. water quench 132 13s 19': 301 327 an 380 cent, at which point hardening begins, to about 4 alloys becomes impaired. The hardened alloys in and/or zirconium for the titanium. In the fol: 5 common with iron-nickel alloys generalLv are lowing table a few typical alloys are given by way characterized by their toughness, resistance to atof example.

5. tack by'non-oxidizing acids, ferro-magnetism and high electrical resistivity. With an increasein the Numb 21 n a m nickel content of the base alloy, the desirable 10 range of titanium, as Just defined. re ai s mbu stantially. the same up to percent nickel conin my a tent, but the capacity for hardening displayed by 8} M u the alloys under consideration, steadily dimin- 1n M ishes with increase in nickel content up to 99% 15 with a range of about 150 to 225 Brlnell hardness Brine an Soft 1000 0. water units. Within the range 01 75 to 96 percent nickel 1mm g$ zgg g g; content, the minimum titanium content necessary to develop hardening, increases from-about percent to somewhat more than 4 percent, the 33 35 2222 aluminum the content of this 20 ry to develop suitable hardening amount being roughly proportional to the excess res ponse varies from about 2.5 to substantially. of nickel over 75 percent. Within this range the 6 percent, the latter percentage marking the aphardness differential developed by heat treatment proximate upper limit of forgability. A pre-. is from about 75 to substantially 100 Brinell units.

ferred range is from 5.0 to 5.5 percent. Titanium when added to many other nickel al- 25 When titamum is used as an alloying element, loys of the face centered cubic lattice type prethe use of commercial term-titanium may introviously noted, permits the formation of alloys duce appreclable quantities af aluminum. and having hardening characteristics similar to the iron-nickel-titanium alloys described. Among the metal of which elements these other base alloys may be mentioned: Iron- Wm appear in the resulting anoy' This content so nickel-copper; iron-nickel-chromium; iron-nickof aluminum is mt harmful and it has been. ebmanganese; nickebcoppfl; nickebchmmium, found in fact that the use of even higher contents and nickel metal. The following table shows sev- 0f allmimlm in combination with n m t! eral malleable alloys exemplifying this fact, the ard n n a nts off rs certa n advanta e n0t-" hardness numbers being expressed in Brlnell ably in accelerating the rate at which the hardenx. units: I ing reaction occurs. As an example of this dis- Number s o 10 11 12 1s 14 10' 10 11 1s 10 4 20 NL --0a.,4 43 so so an 18.4 ms seats a0 20 2o 74 Fe "0.135 58 01 05 00 00 01 1.29 12 a 12 Cu 27.2 19 8.0 1.1 64 '78 10 n.- 1.0 11.0 14.0 0.0

M11 a1 Tl 1.0 3.0 as as 2.5 2.0 as 1.0 3.0 3.0 4 1 4 Soft (1000 0. water queneh)- 127 157 154 153 152 128 194 M0 164 178 4,5 Hard (tempered coo-700 c.)-. 231 211 e02 e15 010 004 284 200 204 017 021 200 2x0 The ranges of the several elements in addition covery, the nickel-iron-titanium alloy including to titanium, may be extended as follows: copper 34.8 percent nickel, 2.2 percent titanium, and 0.3 .5-90%, chromium 3-30%, nickel 2 -99%, and iron percent aluminum, showed no appreciable hard- 2-90,% the titanium being replaceable, under the ening when air-cooled from 1000 degrees centiconditions discussed more in detail hereinafter, by grade. A similar alloy including 34 percent nickfrom .5 10% of titanium-like metals such as alue 2.5 percent titanium, and 1. percent aluminum minum and/or zirconium. These elements may increased in hardness about 110 Brinell units on be associated with each other in any desired air-coolin Bflth'alloys hardened to about 320 amounts to give compositions having certain Spec- Brinell units when furnace cooled. It will also ified characteristics. be appreciated that by the use of hardening The preferred range of titanium is substantially agents in multiple as herein described, it is posfrom 1 to 4 percent. This range is determined sible to secure marked economies in manufacture approximately by the first appearance of hardendue to the ability to use cheaper addition mate- 8Q ing and the substantial disappearance of hot malrials without in any l Sacrificing the 8 leability. When it is desired to retain good hot suits desired in the finished product. and cold working properties in order to permit The diversity of base'compositions amenable shaping by forging, hot rolling, cold rolling, drawto hardening by titanium and aluminum has been ing, or plastic deformation generally, full advandescribed. No common alloying elements in 5 tage cannot be taken of the maximum titanium amounts less than 2 percent have been found to content. In such cases it is preferable to employ interfere with this hardening characteristic with titanium contents ranging from 2.2 to 3.2 percent the exception of aluminum and carbon. The for alloys having a low carbon content and in (effect of aluminum when combined with titanium. which the base is nickel-iron, nickel-copper-iron, has justbeen described. Since carbon forms an d percer.., at which point the malleability of the In such cases as much as 10 percent titanium may be used to advantage.

As has been intimated hereinbefore, desirable results may be obtained by substituting aluminum and niekel-chromium-iron. It will, of course, be understood that in case of castings where workability is not a factor to be considered, a

- much greater range of titanium is permitted with is highly detrimental.

inert titanium carbide, its presence with titanium I This is due to the fact that although the total titanium content may be great enough to indicate vigorous hardening, the

alloy is, in fact, devoid of hardening response. It 75 is highly desirable, therefore, to keep the carbon content as low as is metallurgically feasible. Alloys of this type have been produced with as lit,- tle as .01 percent carbon, yet melts containing as much as 0.40 percent carbon have been produced which displayed good hardening properties, although an inefliciently high titanium content in the alloy was necessary.

It is considered to be within the scope of this invention to provide, in addition to the major elements of composition, such other elements as are commonly used in metallurgy to aid in refining, purifying, degasifying, and otherwise treating the alloy to insure its production in sound, tough, malleable form. These auxiliary elements are:

Percent Manganese ..up to Silicon up to 5 Aluminum up to- 1 Vanadium up to l Zirconium up to 1 Titanium up to A Calcium up to Magnesium up to Boron up to-- V2 The nature and quantity of these accessory elements is determined by the nature of the base alloy in question.

Many characteristics of the hardening action developed by titanium and its equivalents, as described hereinbefore suggest that it is of the socalled "precipitation" type, and that nickel, in association with titanium and/or aluminum, is withdrawn from solid solution concurrently with the rise in hardness on heat treatment. Of course, this is only a possible theory and it is to be understood that we are not bound to this theory.

To bring the alloys under consideration into the softest working. condition, the heat treatment required in all cases is a not'too slow cooling from above a minimum temperature. Most eflicient results are obtained when this minimum temperature is exceeded, but the temperature margin by which it is exceeded is not of very great importance, the upper limit usually being that at which an undesirable coarsening in grain size occurs. The minimum softening temperature varies directly with increase in content of the hardening element or elements, and also varies to some extent with the composition of the base alloy. For contents of titanium and/or aluminum which yield malleable alloys, this minimum temperature is generally from 750 degrees centigrade to 850 deg. centigrade, and can easily be established for a particular alloy. As a general rule the entire group of alloys herein described respond well to a range of softening temperatures varying from 900 deg. C. to 1050 deg. C. The rate of cooling required to avoid hardening is not great, and air cooling will usually prove fast enough, although cooling in water or in oil is permissible.

Where it is desired to heat treat the alloys in order to harden them, the treatment is much more variable. Variations in composition of the base metal, and of the hardening elements affect both the temperature at which the desired hardening is most efiectively produced, and also the rate at which it occurs. In all cases hardening occurs over a considerable range of temperatures, and the lower the temperature at which this can be carried out, the greater will be the hardness ultimately developed. Since the rate of hardening diminishes as the temperature is decreased, an optimum hardening temperature may be appropriately designated. a

With a hardening treatment which includes holding the alloy at a fixed temperature for several hours, the preferred hardening temperature is substantially 700 deg. C. for alloys in which titanium is the hardening element, and about 600 deg. C. when aluminum or zirconium is the hardening element. It is to be noted that when chromium does not exceed about 5 percent, good hardening may be produced by furnace cooling from the softening range. When the chromium content exceeds this value, the hardening reaction proceeds sluggishly, and considerably more time is required in order to develop full hardness. High chromium alloys containing up to 30% chromium may show very little hardening on furnace cooling.

When it is desired to develop the maximum hardness of a given alloy, it has been found advantageous to carry out the hardening operations in several steps at progressively lower temperatures and preferably with the duration of heating increasing at the lower temperatures. The temperature range in which this incremental hardening may be carried out is from the minimum softening temperature above described, down to about 500 deg. C. As a particular example, an alloy of a composition including having an initial Brinell hardness of 148 hardened to 290 Brinell after twenty-four hours of treatment at 700 deg. C. When an incremental hardening heat treatment was given to this alloy,

a hardness of 340 Brinell units was secured, the particular treatment included heating at 750 deg.

C. for two hours, followed by heat treatment at 600 deg. C. forfive hours, and at 600 deg. C. for twenty-three hours.

On the other hand, for the purpose of improving toughness and ductility of the hardened alloy, the termination of the hardening operation may include the step of reheating to a. temperature higher than the last preceding step, but still within the range of temperatures in which the particular alloy is hardenable.

A further example may be given in which the hardening characteristics as described hereinabove are combined with martensitic hardening of the type commonly observed in air-hardening steels. This combination occurs in marginal austenitic nickel-content ferrous alloys of the nickel, nickebchromium, nickel-copper, nickelmanganese and related series in which the iron content is up to about 10 percent lower than that at which martensite ceases to be a constitucut under ordinary conditions of cooling.

Alloysof the aforesaid type when heat treated develop a strengthening precipitate, accompanied by a change in composition of the residual matrix suflicient to shift the latter within the range of compositions which have a true allotropic transformation, and hence, at suitable cooling velocities, can be transformed at least partially into martensite. The following are two examples of tense hardening.

properties at room temperatures,

Brinellhardneesnumber Ni Cr Ti Al l000 C.

' Water Tempered Quench These alloys were both completely austenltic and non-magnetic when in the soft condition, but became magnetic and partially martensitic after heating between 600 and 700 C. followed by cooling in the air.

As exemplifying the physical properties produced in malleable alloys of the type under conable amounts of hardening agents such as titanium, aluminum and/or zirconium. It is to be noted further that the hardenable alloys comprehended within the spirit and scope of the present invention, are adapted for a wide variety of uses, and more particularly for use in structures which can economically be made by plastic deformation such as drawing, pressing, etc., such formed articles being adapted to being suitably hardened by a heat treatment as set forth.

This is a continuation in part application of our:

sideration, the following table is included:

'Prop. Ult. Elong. Red Izod N0. Ni Cu Cr Ti Fe Temper limit strepggth perzcent para? Jun .1 8.0 2.5 Bel. s01: 24,800 87,600 31.5 05.1 30 Hard 110,000 102,000 10.0 33.0

21.1 0.3 2.4 Bal. Soft 24,000 87,800 0&0 59.8

Hard 11,400 158,000 22.0 41.3

21 15.5 12.4 2.1 B81. Soft 24,000 88,000 48 08 102 11811101) 00,000 130,000 00 02 14 Hardib) 80,000 100,000 1 22 i8 50 2a) 700 C. temper.

b) Incremental temper.

In addition to exhibiting these high physical the high strength and elastic properties shown may be retained at high temperatures, provided that the base alloy is of a suitable type; iron-nickelchromium is appropriate, and the titanium alloy 1 with this base shows excellent strength properties at temperatures up to the hardening temper- 90,000 psi PL. 125,000 psi ULT.

. 25% Elong.in2"' 12% Red. area Such alloys are particularly suited for purposes involving considerable heat and loadsuch as ,obtain in steam and internal combustion turbines,

as well as in many chemical processes, a particular example being that of tube stills and like apparatus which may be used in oilcracking and oil refining.

Many alloys, in particular steels, exist which have hardness and tensile properties equal to or even excelling the alloys of the present type. The advantage of the latter lies in the unique fact that the present hardening elements may add hardening properties to particular base alloys without detriment to their other distinctive properties', thus affording a combination of strength with other special qualities not previously possible. For example, the addition of titanium to austenitic nickel-chromium steels imparts hardness and high elastic properties without interfering with the valuable corrosion and heat resisting qualities of the latter. In particular cases in which a property is closely associated with a specific nickel content, e. g., low' expansivity in nickel-iron alloys, a slight adjustment ofcomapplication, Serial No. 356,870, filed April 15, 1929.

What is claimed is: 1. A hard nickel copper alloy containing about 50% to about 85% nickel, at least 1 to about 10% titanium, and copper constituting substantially the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufliciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufficiently high and for a period of time sumcient to obtain a substantial increase in the hardness of the alloy.

2. A hard nickel-copper alloy containing about 50% to about85% nickel, at least 1 to about 4% titanium, and copper constituting substan-' tially. the balance of the alloy, said alloy being age hardened by heating the alloy to an elevated temperature below its melting point but sufliciently high to cause titanium to go into solution, quenching the alloy and reheating to a temperature below that of the initial heating but sufficiently high and for a period of time sumcient to obtain a substantial increase in the ture below that of the initial heating but sufliciently high and for a period of time sufiicient to obtain a substantial increase in the hardness of the alloy.

4. A hard nickel-copper alloy containing about 50% to about 85% nickel, at least 1% to about I 10% of titanium and copper constituting sub stantially the balance of the alloy. said alloy being age hardened by heating for a. suiiicient period of time and at a sufliciently high temperature between 750 C. and the melting point to dissolve at least a portion or titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suilicient period of time and at a suiiiciently hi h temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

5. A hard nickel-copper alloy containing about 50% to about 85% nickel, at least 1% to about 4% of titanium and copper constituting substantially the balance of the alloy, said alloy being age hardened by heating for a suflicient period of time and at a sufllciently high temperature between 750 C. and the melting point to dissolve at least a portion or titanium in the'alloy, cooling the alloy to a temperature below 750 .0. and heating the alloy for a suflicient period of time and at a sufliciently high temperature below 750 C. to obtain a substantial increase in the hardness of the alloy.

6; A hard nickel-copper alloy containing about 50% to about 85% nickel, about 2.2% to about 3.2% of titanium and copper constituting substantially the balanceoi the alloy, said alloy being age hardened by heating for a suflicient period of time and at a sumciently high temperature between 750 C. and the melting point to dissolve at least a portion of titanium in the alloy, cooling the alloy to a temperature below 750 C. and heating the alloy for a suiiicient period of time and at a suiiiciently high temperature below 750' C. to obtain a substantial increaseinthehardnessoithealloy.

7. Ahardnickel-copper alloyoontainingabout 50% to about 85% nickel, at least 1% to about 10% titanium, and copper constituting substantially the balance 01' the alloy, said alloy being hardened by heating for a suflioient period of time at a sumciently high temperature between 5 750 C. and the melting point of. the alloy to cause at least a portion of titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C..at a rate sufllcientby slow to cause a substantial increase in the 10 hardness oi the alloy.

8. A hard nickel-copper alloy containing about 50% to about 85% nickel, at least 1% to about 4% titanium, and copper constituting substantially the balance of the alloy, said alloy being hardened by heating for a suflicient period of time at a sumciently high temperature between 750 C. and the melting point 01' the alloy to cause at least a portion oi the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate sufliciently slow to cause a substantial increase in the hardness of the alloy.

9. A hard nickel-copper alloy containing about 50% to about 85% nickel, about 2.2% to about 3.2% titanium, and copper constituting substantially the balance of the alloy, said alloy being hardened by heating for a sumcient period 0! time at a suiiiciently high temperature between 750 C. and the melting point of the alloy to cause at least a portion of the titanium to dissolve in the alloy, and cooling the alloy from the aforesaid temperature to about 500 C. at a rate suiiiciently slow to cause -a substantial increaseinthehardnessoitheailoy.

NORMAN B. FILLING. PAUL D. MERICA.