US2864697A - Titanium-vanadium-aluminum alloys - Google Patents

Description

Unite TITANlUM-VANADlUM-ALUMINUM ALLOYS Application January 23, 1956, Serial No. 560,512

6 Claims. (Cl. 75175.5)

The invention relates to titanium-base alloys and more tates Patent lice particularly to ternary alloys of titanium with vanadium and aluminum.

The increasing use of titanium and titanium alloys has 7 resulted in commercial requirements for a titanium alloy,

particularly adapted for being rolled into sheet material in which high ductility may be developed to permit form-, 1 ing and in which high strength may be developed after-' forming. In other words, a need exists for titanium s'heet'i,

condition at room temperature should have a maximum ultimate tensile strength of 120,000 p. s. i., a maximum yield strength of 110,000 p. s. i., a minimum elongation of 15% a maximum bend ductility of 2T, uniform elongation of 10%, and a maximum ratio of 0.9 of yield strength to ultimate strength;

(b) The material should be capable of being aged by heat treatment at a temperature in the neighborhood of 1000" F. and preferably for less than eight hours to develop at room temperature a minimum ultimate tensile strength of 170,000 p. s. i., a minimum yield strength of 155,000 p. s. i., and an elongation of 10%; and

(c) The material at a temperature of 800 F. and after solution treating and aging should have an ultimate tensile strength of 115,000 p. s. i. and a yield strength of 87,000 p. s. i. and must be able to withstand 35,000 p. s. i. at 800 F. for 500 hours and deform no more than 1% under such conditions.

We have discovered that the desired combination of properties may be obtained in sheet alloys of the present invention and that the best combination of most desirable properties may be obtained in a titanium base alloy containing substantially 15% V and 2 /z% Al. These alloys have excellent forming properties as solution treated in the alpha-beta field or the beta field, and subsequently can be aged to very high strength levels.

The improved titanium-vanadium-aluminum alloys of the present invention have relatively low strength levels and an unusually large spreadup to about 71,000 p. s. i.'betW-een yield strength and ultimate strength as solution treated in the alpha-beta field or the beta field. The ternary titanium base alloy containing 15% V and 2 /2% Al exhibits the best combination of low strength, a high spread between yield strength and ultimate strength, and high ductility in the solution treated condition. Fur- 7 2,864,697 Patented Dec. 16, 1958 thermore, the titanium-vanaditmi-aluminum alloys of the present invention may be subjected to a simple aging treatment to substantially double the ultimate strength and to increase the yield strength by as much as 110,000 p. s. i.

Furthermore, we have discovered that the titaniumvanadium-aluminum alloys of the present invention having the indicated properties are further characterized by having excellent uniform elongations as well as high elongation values. Normally titanium alloys do not exhibit uniform elongation, and the provision of a highly ductile titanium alloy having high uniform elongation values is unusual. Uniform elongation is measured in the portion of the gage length of the tensile specimen outside the necked-down area.

For instance, when a sheet tensile specimen is subjected to a tensile test and is pulled, titanium alloys usually neck inward sharply and fail in a short length of the specimen between the gage marks. However, sheet tensile specimens made from the improved alloys of the present invention, when subjected to tensile tests do not necessarily fail between the gage marks but sometimes fail 7 beyond the same. Furthermore, areas within the range of the gauge marks-Which were initially marked with /s" squareselongated the square markings about 25% in all /2 sections of the specimen.

Thus, sheet material formed from the improved titanium alloysof the present invention and having the high uniform elongation values described stretch more or less uniformly over the entire area under stress. Uniform elongation is important in forming operations as it is an indication of how much forming can be done on a part, before necking down takes place. The achievement of this characteristic is very important since it provides a kind of ductility permitting the material to be subjected to complicated forming, stamping or deep drawing operations.

Accordingly, it is a general object of the present inven tion to provide a new heat treatable titanium-vanadiumaluminum sheet alloy which may be solution treated topermit forming While highly ductile at low strength levels and thereafter aged to extremely high strength levelsl Also, it is an object of the present invention to provide a new titaniurn-vanadium-aluminum sheet alloy which may be heat treated by heating and quenching to very low strength levels, with reasonably high ductility and excellent formability. i

It is another object of the present invention to provide a titanium-base vanadium-aluminum sheet alloy which as solution treated in the alpha-beta field or the beta field is highly ductile and at the same time exhibits high uniform elongation values. 1

Another object of the present invention is to provide. a titanium-base vanadium-aluminum sheet alloy in which the ultimate strength may be increased as much as twice by a simple aging treatment after forming.

Still another object of the present invention is to provide a titanium-base vanadium-aluminumsheet alloy hav ing a desirable combination of low strength, a large spread between yield strength and ultimate strength, and high ductility in the solution treated condition.

Finally, it is an object of the present invention to provide a new ternary titanium-vanadium-aluminurn sheet alloy and particularly an alloy of titanium and 15% V and 2V2 Al.

Certain of the properties of alloys of the present invention are shown in the drawings in which:

Fig. 1 is a graph illustrating the yield strength, ultimate strength and elongation of alloys of the present invention made with 138. BHN sponge titanium base, solution treated in the beta field as well as solution treated in the beta field and then aged;

Fig. 2 is a graph similar to Fig l of alloys made from 106 BHN sponge titanium base;

4 erties for achieving the objectives and new results of the invention.

The alloys of the present invention after melting and casting may be processed in the usual manner and forged or rolled to form the desired wrought semi-finished or finished product. For instance, ingots of the improved titanium-vanadium-aluminum alloys may be forged or bloomed to slab form, hot rolled to sheet bar, and the sheet bar hot rolled to form finished sheets, say, .030" thick, at about 1400 F.

Since the alloys of the present invention are intended to be subjected to forming operations in the solution treated condition, it is only necessary that the material have some ductility as hot rolled. Typical data and ashot-rolled physical properties (longitudinal) of .030" sheet rolled from alloys containing vanadium and various amounts of aluminum made from sponge having various strength levels are given in Table I below as follows:

TABLE I As hot rolled physical properties (longitudinal) Ultimate Yield Elonga- Sponge Beta Heat No. Nominal Tensile Strength tlon, T-Bend Hard- Trunsus,

Composition Strength, (0.2% off Percent (Long) ness, F.

p. s. i. set), p. s. i in 2 BHN Fig. 3 is a graph similar to Fig. 1 of alloys made from 138 BHN sponge titanium base but solution treated in the alpha-beta field; and

Fig. 4 is a graph similar to Fig. 3 of alloys made from 106 BHN sponge titanium base solution treated in the alpha-beta field.

The alloys of the present invention may be prepared from either commercial titanium or high purity titanium. Where prepared from commercial titanium, a typical analysis of the material in addition to titanium, vanadium and aluminum, is 0.02% C., 0.01% N 0.10% 0 and 0.005% H However, the invention is not restricted to the use of material having the typical interstitial level indicated, as the level may be of the order of 0.06% C., 0.03% N 0.15% 0 and 0.019% H In other words presently available sponge having an average sponge hardness of 120 BHN is suitable and this hardness may fall in the range of 106 BHN to 138 BHN. Thus, in examples given below, titanium sponge having different typical interstitial levels was used such as 106 BHN and 138 BHN sponge.

In practice, the titanium is preferably melted by the electric arc process in a water-cooled copper crucible in a vacuum or an atmosphere such as argon and the alloying elements are added to the melt either as chemically pure components or in the form of a high purity vanadiumaluminum alloy. The latter is preferable because the commercial master vanadium-aluminum alloy available is substantially cheaper in cost than pure vanadium. Also, the master alloy is well adapted without further additions of either vanadium or aluminum to form the preferred 15 V-2.5 Al alloy with titanium.

In general, the alloys of the present invention comprise from 12 to percent vanadium and from 1 to 4 percent aluminum, the balance being all titanium. More particularly, the preferred alloys of the present invention comprise from 14 to 16 percent vanadium and from 2 to 3 /2 percent aluminum, the balance being all titanium. A 15% V-2/: Al alloy with the balance being all titanium is preferred as it exhibits the best combination of prop- The beta transus temperatures listed in Table I were determined from .080" sheet; and although some discrepancies in these temperatures may be noticed, there is anaverage 20 F. increase in the transus in going from 106 to 138 BHN sponge, and an increase of about 40 F. for each percent aluminum added.

The physical properties of the heats listed in Table I in the solution treated and solution-treated-and-aged conditions are shown graphically in Figs. 1 to 4. Solution treatment temperatures were selected 50 F. above and F. below the beta transus, respectively, for solution treatment in the beta field and solution treatment in the alpha-beta field. After heating, the specimens were water quenched to retain the phase at which solution treatment takes place. All specimens in the aged condition were aged twenty-four hours at 900 F. and then air cooled, which should over-age these alloys.

The beta-quenched graphs are indicated at B4, B-2 and B-3 in Figs. 1 and 2 illustrating, respectively, ultimate tensile strength, yield strength, and elongation values; and corresponding beta-quenched and aged graphs are indicated at B-IA, B-2A and B-3A in Figs. 1 and 2. Similarly, alpha-beta. quenched graphs are indicated at AB-l, AB-2 and AB3 in Figs. 3 and 4, the alpha-beta quenched and aged graphs being indicated at AB1A, AB-ZA and AB-3A in Figs. 3 and 4.

i In general, referring to Figs. 1, 2, 3 and 4, the higher interstitial level gives higher strength levels after aging. Compare graphs B-IA and B-ZA for 138 BHN sponge of Fig. l with similar graphs of Fig. 2 of material made from 106 BHN sponge. Solution treated properties show little difference sponge lots.

The alloys show low strength levels (see graphs B-1 and 3-2 and AB-l and AB-.2 in Figs. 1 to 4) and an unusually large spread bctween yield strength and ultimate strength as solution treated in either the alpha-beta field or the beta field. Note the distance between graphs B1 and 8-2 in Figs. 1 and 2 and between graphs AB-1 and A34 in Figs. 3 and 4 in the range of from 1 to 4 percent aluminum.

The 15 V-2.5 Al-Ti composition exhibits the best combination of low-strength (graphs B-1 and B-2 and AB-l and AB-Z), high yield stlength to ultimate strength spread, and high ductility (graphs B-3 and AB-3) in the solution treated condition.

The maximum ultimate tensile strength in each instance is very close to the 120,000 p. s. i. requirement given above, but the maximum yield strength in every instance is far below the 110,000 p. s. i. maximum specified requirement. Similarly the elongation value in each instance is near to the 15% requirement, but the ratio of yield strength to ultimate strength is far below the required 0.9 maximum value.

The high elongation values exhibited by the 15 V-2.5 Al-Ti alloys are also uniform elongations, uniform elon- Sheets rolled from the improved alloys may beformed;

as by stamping, deep drawing and the like into products or articles of the desired configuration after solution treatment, and such formed parts are subsequently agedto develop the high strength levels therein desired.

The stability of the beta quenched condition at ambient temperatures is shown in the following Table III for aging times of 50 and 100 hours. The results indicate that the yield strength is increased about 20,000 p. s. i. after 50 and 100 hours aging while the ultimate strength and elongation values remain about the same. However, the uniform elongation, particularly after 100 hours, is not as good as in the quenched condition. In use, if this slight age-hardening proves undesirable, the sheet 15 should "be solution-treated just before forming.

TABLE III Stability tests on the solution treated 15 V-2.5 Al-Ti Alloy YS, p. s. i. Elong., T-Bend Uniform Elonga- Aging Time at Dir. UTS, (0.2% percent tlon, Percent 150 F., Hrs. p. s. i. Offset) in 2 in l/ L 101, 900 39,300 15. 6 1. 8 6. 3 12. 18. 8 T 100,700 43. 200 29. 7 1. 8 21. 9 28. 1 28. 1 50 L 101, 800 58, 500 14. 8 1. 1 6. 3 9. 4 12. 5 T 97, 800 62, 200 17. 2 2. 6 20. 3 23. 4 18.8 100 L 99, 900 57, 300 14. 4 1. 3 17. 2 6. 3 6. 3 T 98,800 65,200 25.8 2.1 23.4 9.4 9.4

gation being measured in the portion of the gage length of the tensile specimen outside the necked-down area. The V-2.5 Al-Ti alloy has a 29.7% total elongation in 2" while the percent elongation in /2 gage sections was 21.9, 28.9 and 28.1. Such uniform elongation values are much greater than the indicated requirement.

The high ductility and large spread between yield and ultimate strength in the solution treated 15 V-2.5 Al-Ti alloy indicates good forming characteristics. The exact explanation of the reasons why these particular proper-. ties are developed is not clear, although there is evidence leading to the conclusion that the properties may be attributed to a martensitic reaction occurring during stressing. First, the 15 V-Ti binary has barely enough V to be quenched to retained beta, and the addition of Al apparently makes the alloy a borderline case between a beta-stabilized alloy and a martensitic titanium alloy. Second, the as-beta quenched microstructure is clear beta but develops a martensitic structure after tensile testing.

As indicated in the graphs, aging the solution treated alloys of the present invention results in high strength levels and low elongation. Quenching from the alphabeta field gives slightly higher aged ductility and somewhat lower strength levels. The lower interstitial level seems to give higher ductility.

Typical annealed properties of the 15 V-2.5 Al-Ti alloy are given in Table II below:

The alloys of the present invention have good solution treated properties even when beta quenched. The 15 V- 2.5 Al-Ti alloy exhibits the best combination of properties. It has good solution treated properties even when beta quenched and fair ductility at aged strength levels of 150,000 to 200,000 p. s. i. UTS. The alloy sheet has excellent uniform elongation and a large spread between yield strength and ultimate strength in the solution treated condition. As beta quenched, the 15 V-2.5 Al-Ti sheet is fairly stable up to one hundred hours at 150 although some loss of uniform elongation occurs. To summarize,

typical physical properties of .030" sheet made from the 15 V-2.5 Al-Ti alloy, are as follows:

Such properties provide sheet material having excellent formability in the solution treated condition.

In a series of tests comparing the unusual uniform elongation characteristics of the 15 V-2.5 Al-Ti alloy of the present invention with the uniform elongation values TABLE II Annealed properties of 15 V-'2.5 Al-Ti .040 sheet YS, Elong, Bend Heat Treatment Dir. UIS, p. s. i. Percent p. s. i. (0.2% 1D. 2"

Offset) I T 1,250 F.% hr.FC to 900 F.AC L 124, 500 106,700 8. 2 1.6 l,250 F.% hr.-FC to 900 F.AO 'I 130, 700 114,200 8. 2 2.6 l,250 F.% hr.FO900 F.AC, 8001 hlZ-AO..- L 123, 500 107, 600 7. 8 1.3 1,250 F.% hr.-F C900 F.AG, 8001 h1.AC.. T 131, 200 116, 400 8. 2 2. 6

the alloys tends to give a massive alpha precipitate at the prior beta grain boundaries, after aging.

of other titanium alloys which had appeared promising in this respect, the 15 V-2.5 Al-Ti alloy sheet showed very good uniform elongation properties in both the longitudinal and transverse direction in the solution treated con- I dition and showed by far the best uniform elongation characteristics of all of the alloys checked in the solution treated conditiom The uniform elongation curves for both transverse and, longitudinal sheet test specimens of the new V 2 .5 Al-Ti alloy', show a minimum of 10% uniform elongation with several plateaus showing greater uniformelongation. Qne ofLthe plateaus for both transverse and longitudinal specimens is above uniform elongation. However, the improved alloy shows poor uniform elongation in the solution treated, and aged condition,

These tests were conducted on, standard .040" strip tensile specimens with straight reduced sections (i. e., no taper was. machined in the gage length). The tensile specimens were marked with a, /s square gridover the 2" gage length. The specimens were pulled, usinga constant strain rate of .005-in/in./min. to a point past the .2% offset yield point. The percent elongation for each A" was calculated, anda graph. usingthepercentelongation for the ordinate and the length along the 2" gage length as the abscissa was plotted for each specimen.

The shape of the curve formed was the determining factor as to whether the uniform elongation was considered to be good or poor. A curve with plateaus and not jagged peaks was. considered to show good uniform elongation.

The strength levels of these .040" sheet tensile specirnens tested in the solution treated and in the solution treated and aged conditions were asfollows:

In making. these uniform elongation tests, the solution treatment includedheating at 1370 F. for one-half hour and then water-quenching, and the aging involved heating solution-treated material at 900 F. for twenty-four hoursand then air cooling;

Although. the alloys of the present invention have-been described particularly as sheet alloys, the use of the same is not limited to the manufacture of sheet material as the unusual properties can be availed of in other kinds of rolled: or forged semi-finished or finished titanium alloy products, herein termed wrought products.

It is to be understood that in the foregoing tables, where intended composition is indicated, there may be some small variation in actual composition determined by chemical analyses. Compositions usually are close to the nominal or intended composition but may vary slightly either way from the intended values; depending upon the ability to control the exact amount of alloying additions made and upon the exact proportions of aluminum and vanadium in the Al-V master alloy which may be used.

The sheet alloys of the present invention accordingly provide a heat treatable material that may be solution treated to low strength levels with reasonably high duetility and a large spread between yield strength and-ultimate tensile strength, thereby providing excellent formability. The solution treated or solution treated and formed material may then be aged to high strength levels.

In the foregoing description, certain terms have been used for brevity, clearness and understanding; but noun necessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are utilized for descriptive purposes herein andnot for the purpose of limitation and are intended construed.

Having now described the invention, the features, discoveries and principles thereof, thecharacteristics of. the

to be broadly new alloys, and thenew anduseful results obtained, the

new and useful compositions,

combinations, products, dlSCOV6IlS,- and prmclples, and

reasonable mechanical p. s. i. between yield strength 8 equivalents thereof obvious to those skilled in the art ire set forth in the appended claims.

We claim:

1. A rolled heat treated titanium base alloy sheet product formed of a titanium base alloy consisting of 14% to 16% vanadium, 2% to 3 /2% aluminum, and the balance titanium with incidental impurities; said product being characterized by having in the solution-treated condition a ratio of yield strength to ultimate tensile strength from about 0.9 to as low as 0.5, an ultimate tensile strength less than 120,000 p. s. i., elongation in excess of 15%, and uniform elongation in excess of 10%.

2. A rolled heat treated titanium base alloy sheet prod uct. formed of a titanium base alloy consisting of 14% to 16% vanadium, 2% to 3 /2% aluminum, and the balance titanium with incidental impurities; said product being characterized by having in the solution-treated condition a ratio of yield strength to ultimate tensile strength from about 0.9 to as low as 0.5, an ultimate strength less than 120,000 p. s. i., elongation in excess of 15%, and uniform elongation in excess of 10% permitting forming of the sheet product at such low strength levels; and said sheet product having an ultimate tensile strength of from 150,000 to 200,000 p. s. i. when aged at 900 F. after solution treatment.

3. A Wrought heat treated titanium base alloy product formed of a titanium base alloy consisting of 14% to 16% vanadium, 2% to 3%% aluminum, and the balance titanium with incidental impurities incident to the use of commercial titanium sponge having a hardness in the range of 106 to 138 BHN; said product being characterized by having in the solution-treated condition a ratio of yield strength to ultimate tensile strength from about 029' to as low as 0.5, an ultimate tensile strength less than 120,000 p. s. i., elongation in excess of 15%, and uniform elongation in excess of 10% permitting forming of the product at such low strength levels; and said product having an ultimate tensile strength of from 150,000

to 200,000 p. s. i. when aged at 900 F. after solution treatment.

4. A rolled heat treated titanium base alloy sheet product formed of a titanium base alloy consisting of 15% vanadium, 2 /2% aluminum, and the balance titanium with incidental impurities; said product being'characterized by having in the solution-treated condition a yield strength as low as 40,000 p. s. i., an ultimate tensile strength less than 120,000 p. s. i. to as low as 95,000 p. s. i., a ratio of yield strength to ultimate tensile strength from about 0.9 to as low as 0.5, elongation of from 15% to 25%, and uniform elongation in excess of 10% permitting forming of the sheet product at such low strength levels; and sail sheet product having a yield strength in excess of 160,000 p. s. i. and an ultimate tensile strength in excess of 175,000 p. s. i. when aged at 900 F. after solution treatment.

5. A rolled heat treated titanium base alloy sheet product formed of a titanium base alloy consisting of 14% to 16% vanadium, 2% to 3 /2% aluminum, and the balance titanium with incidental impurities; said product being characterized by having in the solution-treated condition a ratio of yield strength to ultimate tensile strength from about 0.9 to as low as 0.5 with a spread of up to 71,000 p. s. i. between yield strength and ultimate tensile strength, elongation in excess of 15 and uniform elongation in excess of 10%; and said sheet product having an ultimate tensile strength of from 150,000 to 200,000 p. s. i. when aged.

6. A rolledheat treated titanium base alloy sheet product formed of a titanium base alloy consisting of 14% to 16% vanadium, 2% to 3 /2% aluminum, and the balance titanium with incidental impurities; said product being characterized by having in the solution-treated condition a ratio of yield strength to ultimate tensile strength from about 0.9 to as low as 0.5 with a spread of up to 71,000 and ultimate tensile strength,

, '9 N 10 elongation in excess of 15%, and uniform elongation in References Cited in the file of this patent excess of 10%; and said sheet product when aged having an ultimate tensile strength substantially twice that of its UNITED STATES PATENTS ultimate tensile strength in the solution-treated condition 2,754,204 Jaffee et a1. July 10, 1956 and a yield strength increased as much as 110,000 p. s. i. 5 a from the yield strength of the product in solution-treated FOREIGN PATENTS condition. 1,094,616 France Dec. 8, 195

Disclaimer 2,864,697.Lee S. Busch, George W. Bauer and Paul E. Moor'heacl, Varren,

Ohio. TITANIUM-VANADIUM-ALUMIN UM ALLOYS. Patent dated Dec. 16, 1958. Disclaimer filed July 13, 1966, by the assignee, National Distillers dc Chemical Como ration. Hereby enters this disclaimer to claims 1 through 6 inclusive of said patent.

[Oyficlal Gazette August 23, 1966.]

Claims (1)

1. A ROLLED HEAT TREATED TITANIUM BASE ALLOY SHEET PRODUCT FORMED OF A TITANIUM BASE ALLOY CONSISTING OF 14% TO 16% VANADIUM, 2% TO 3 1/2% ALUMINUM, AND THE BALANCE TITANIUM WITH INCIDENTAL IMPURITIES; SAID PRODUCT BEING CHARACTERIZED BY HAVING IN THE SOLUTION-TREATED CONDITION A RATIO OF YIELD STRENGTH TO ULTIMATE TENSILE STRENGTH FROM ABOUT 0.9 TO AS LOW AS 0.5, AN ULTIMATE TENSILE STRENGTH LESS THAN 120,000 P.S.I., ELONGATION IN EXCESS OF 15%, AND UNIFORM ELONGATION IN EXCESS OF 10%.

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