US3595645A - Heat treatable beta titanium base alloy and processing thereof - Google Patents

Abstract

A TITANIUM BASE ALLOY CONSISTING ESSENTIALLY OF ABOUT 7 TO 9% EACH OF MOLYBDENUM AND VANADIUM, 1.5-2.75% IRON, 2.5 TO 3.5% ALUMINUM AND THE BALANCE TITANIUM.

Description

HEAT TREATABLE BETA TITANIUM BASE ALLOY AND PROCESSING THEREOF Filed March 16, 3.966

lo @om manor xmc' wzq OhrJ ON ISd OOOlX-HLNiLS CIIBI .LISddO 'ZZO :NvaNTOR- B. HUNTEQ Harem' w. reosemaaaq DONQLD QTTOQNEVS United States Patent O 3,595,645 HEAT TREATABLE BETA TITANIUM BASE ALLOY AND PRCESSING THEREOF Donald B. Hunter and Harry W. Rosenberg, Henderson,

Nev., assignors to Titanium Metals Corporation of America, New York, N.Y.

Filed Mar. 16, 1966, Ser. No. 534,759 Int. Cl. C22c 1 5/ 00 ABSTRACT OF THE DISCLOSURE A titanium base alloy consisting essentially of about 7 to 9% each of molybdenum and vanadium, 1.5-2.75% iron, 2.5 to 3.5% aluminum and the balance titanium.

The invention described herein may be manufactured and used by or for the Government for governmental purposes Without the payment of any royalty thereon.

This invention pertains to heat-treatable, beta titaniumbase alloys, and more particularly to a novel alloy of this type of critically-limited alloy content such as to impart a combination of useful properties rendering the same superior in Various respects to previously known titaniumbase alloys of the substantially all-beta type.

The alloy of the invention consists essentially as to composition of about 7 to 9% each of molybdenum and vanadium, 1.5 to 2.75% of iron, 2.5 to 3.5% aluminum, and the balance titanium except for interstitials and impurities within commercial tolerances. The preferred cornposition of the alloy for most commercial applications is about 8% each of molybdenum and vanadium, 2% iron and 3% aluminum, balance substantially all titanium.

As missions become more sophisticated, and as aerospace vehicles become larger, the more important structural efficiency becomes. Structural efciency entails not only high ratios of strength to weight but also resistance to all forms of cracking. Moreover, in order that a designer can take maximum advantage of an alloys tensile properties, these properties must be attainable throughout sections of varying thickness under a wide variety of service conditions. Notched fatigue strength, crack initiation and propagation resistance and metallurgical stability are particularly important. The alloy of this invention represents an improvement in the present state of the art in these respects.

Also from the producers and fabricators points of view, formability and aging response are important aspects in component manufacture. The alloy of this invention as solution treated above the beta transus has a relatively low yield strength on the order of 120,000 p.s.i., 0.2% offset and excellent ductility on the order of 16% elongation in 2" for ease of forming. As thereafter aged at about 900 F. for a relatively short time of about 24 hours, the ultimate and yield strengths are increased to about 200,000 and 190,000 p.s.i., respectively, with retention of good ductility of 5% or better in tensile elongation. A unique property of the aged strength of the alloy is that it remains substantially constant at the above level on further prolonged aging treatment, and in this respect dilers remarkably from the commercial Til3Vl1Cr3Al alloy, the aged strength of which progressivey increases with time of aging treatment and never attains the relatively constant plateau strength of the instant alloy. Also the aged yield strength of the instant alloy increases much more rapidly with aging time than that of the commercial alloy. Thus the aged ultimate strength of the instant alloy attains a value of 180,000 p.s.i. in 8 hours as against only about 138,000 p.s.i.. of the commercial alloy within that aging period. Also as developed below the alloy of this invention is superior in various other respects to the Ti-l3V-llCr-3A beta alloy, which heretofore has been the best commercial alloy of this type.

The alloy of the present invention may be produced as flat rolled mill product or in such other forms as forgings, extrusions or wire by conventional fabrication techniques. The room temperature and 600 F. tensile properties of the preferred Ti-8Mo-8V-2Fe-3Al modification are shown in the following Tables l and II:

TABLE L-ROOM TEMPERATURE TENSILE PROPERTIES OF Ti-8 Mo-S V-2 Fe-3 Al. AGED AT 900 F.

[0.060" thick sheet, solution treated 1,500" F.-10 minutes-Water 1 Sample aged after machining and tested with oxidized surface.

TABLE IL600 F. TENSILE PROPERTIES [0.060 thick sheet solution treated as above] Elongation percent in 2" Aging heat UTS YS Unitreatment K s.i. K s.i. Local form Total Modulus 8 hours-AQ..- 167 142 10 1 4 14. 6 24 l1ours-AC 170 154 22. 5 1. 25 3. 5 14. 0

From the data of Table I it will be seen that the alloy of this invention when recrystallized by aging from the solution-treated conditions attains a yield strength of 180,000 p.s.i., i.e. 180K s.i. after aging for 8 hours at 900 F., and therea'fter prolonging the aging time to 64 hours results in only a small further strength increase up to about K s i. attained in 24 hours.

This is also shown graphically in the accompanying drawing which also shows the aging response f-or the commercial Ti-13V-l1Cr-3Al alloy. Note that after aging for 8 hours at 900 F., Ti-SMo-SV-2Fe-3Al reaches a, plateau of high strength in the range of 180-190K s.., whereas the commercial alloy Ti-l3V-11Cr-3Al possesses a yield strength of only 140K s.i. and continues to gain strength with increasing Aaging time, so that no plateau of constant strength is attained within 32 hours. This therefore is an important advantage of Ti-8Mo-8V-2Fe-3Al over Til3V- 11Cr-3Al, that it ages rapidly to a 180K s.i. yield strength, and thereafter undergoes little change in strength. This lack of a critical time for aging the Ti-8Mo-8V-2Fe-3Al alloy thus constitutes an important aspect of this invention. Furthermore, whereas the Ti-13V-llCr-3Al alloy is very difiicult to age to a preselected strength level, the aged strength of Ti-SMo-8V-2Fe-3Al alloy can be readily controlled by selection of proper aging temperature. Higher aging temperatures result in lower strength and vice versa.

Moreover, as shown by the test data of Table II above, the alloy of this invention retains a useful degree of strength up to 600 F. That is to say, in the aged condition the alloy typically retains up to 600 F., 80% 0f its room temperature strength.

The notched fatigue properties of the alloy of this invention are shown below in Table III, from which it will be evident that the notched fatigue run out strength of the Ti-8Mo8V2Fe3Al alloy lies in the range of 30-35K s.i.

By contrast the notched fatigue limit of the commercial 10 Ti-l3V-l1Cr-3Al alloy is only 20-25K s.i. at run out time of 10'1 cycles. This superiority in notch fatigue is another important feature of this invention.

TABLE III Room temperature notched fatigue properties 1 (Specimen heat treated 1450 F.-10 min- AC +900 F.-8 hrs-AC) 1 Sheet specimens tested at a minimum to maximum load 3 ratio (R) of 0.25 at a notch concentration factor of K:3.5.

TABLE IV.-SUMMARY OF PROPERTIES OF Ti8 M08 V-2 Fe 3 Al ALLOY (0.060 SHEET) v Property Value Density, lb./cu. inch 0. 175 Aunealed yield Strength, K s. 118-120 Annealed strength/weight ratio, in.- 680, 000 Aged yield strength:

900 F.-8 hours age (strength weight ratio) K s.i. l 180 900 F.-16 hours age (strength/Weight ratio) K s.i 2 186 900 F.-24 hours age (strength/weight ratio) K s.i... 3 191 Room temperature notch tensile:

900 F.8 hours age, K s.i.- 172 NTS/UTS ratio 4 0.87 900 F.-24 hours age, K s i. 164 NTS/UTS ratio 0. 83 -65 F. Notch tensile (900 F.8 hours AC) K s.1 145 600 F. notch tensile:

900 F.-8 hours age, K s.i. 184 NTS/UTS ratio 1.10 900 F.-24 hours age K s 188 NTS/UTS ratio 1. Kre value; 900 F.8 hours age, 45,000 Notched fatigue strength, 900 F.-8 hours age, K s 5 30-35 Minimum bend radius; 1,500 F.-10 minutes-AO 2T 1 7% elongation (1,030,000 in.1).

2 7% elongation (1,060,000 in.1).

3 5% elongation (1,090,000 in.1).

4 Notched tensile strength/ultimate strength ratio. Stress for 10 million cycles.

A further feature of this invention is that Ti-8Mo-8V- 2Fe3Al alloy displays a superior resistance to stress corrosion cracking at 800 F. induced by the presence of salt, Table V below, than the commercial beta alloy Ti-13V-11Cr-3Al. In view of the growing importance of the relative susceptibility of titanium alloys to stress corrosion, this also constitutes an important advantage of this invention over the present state of the art.

TABLE V.COMPARISON OF HOT SALT STRESS CORROSION BEHAVIOR OF T1-8 M0-8 V2 Fe-3 Al .AND Ti-l3 V11 Cr-3 Al ALLOYS (BOTH IN SOLUTION TREATED AND AGED CONDITIONS) Bend Result of Alloy radius Treatment attening 'Tl-8 Mo-B V-2 Fe-B Al 6T None (control) No cracks. Seme as above 6T 800 F.-2 hours, no salt Do. Do- 5. 6T 800 F.-2 hours, salt coated,..- Do. Do--. 5.71 do Do. Do 6T -....do Do. 'Pl-13 V-11 (Jr-3 A1-.. 5. 8T None (control) Do. Same as above 5. 8T 800 F.-2 hours, no salt Do.

o 5. 8T 800 F.-2 hours, salt coated Numerous small cracks. Do 5.8'1 do Do. Do... 5.8'1 do Do.

The following Table IV gives a summary of the mechanical properties of Ti-8Mo8V2Fe-3Al. From this it is seen that this alloy possesses good notch toughness, even in the fully aged condition, (900 F.-24 hours), and

also retains good notch toughness over a range of temperatures from F. to 600 F. This notch toughness is an important feature of this invention.

From the above data it will be seen that whereas the alloy -of the instant invention is immune to salt corrosion cracking under the conditions o'f testing, the Ti-l3V- 11Cr-3Al alloy of the prior art was not.

A further useful property of Ti-8'Mo-8V2'Fe-3Al alloy of this invention is that even after exposure to temperatures of 600 F. for 500 hours under load it sill retains a useful amount of ductility 'as shown in the following Table VI. Ductility is also found when samples of this alloy are tested after exposure to aging temperature without subsequent pickling to remove the oxidized surface, Table I.

TABLE VI.CREEP STABILITY DATA ON Tl-8 Mo-S V-2 Fe3 Al ALLOY Exposure Elon- Percent gation Tempera- Stress, Time, defor- UTS, YS, percent Modulus ture, F. K s.i. hours mation K s.i. K s.i. in 1" p.s.i. X100 l Heat treatment prior to exposure -1,500 F. for 10 minutes and water quenched followed by aging at 900 F. for 8 hours and air cooled. 1 Same as above except for aging424 hours.

From the standpoint of practical useage it is important that titanium alloys be Weldable. Data in Table VII below, shows that Ti-8Mo-8V-2Fe-3Al alloy has good ductility in the as-welded condition, and that by aging for a short period at 900 F. (2 hours) a simultaneous increase in both strength and ductility can be brought about. The application of a short post-Weld aging cycle to improve the properties of the alloy of this invention is a further important point. Table VII shows that by prolonging the aging time at 900 F. to 4 hours, weldments may attain a strength of over 180 K s.i., with good ductility. By aging at 1100 F. a condition of intermediate strength With ductility is produced. By contrast, aging Ti-lSV-llCr-3Al alloy at 1100 F. following welding results in embrittlement. Hence, variation of aging temperature in the range 900-1100 F. -is less important for Ti-8Mo-8V-2Fe-3Al weldments than Ti-13V-11cr-3Al weldments and the lack of a critical post-Welding aging temperature constitutes another aspect of this invention.

TABLE VIL-WELDED PROPERTIES F '1i-8M0-sv-21re-3A1 ALLOY (BUTT WELDS, NO FILLER, 0.060 SHEET HEAT TREATED 1,500 F.-10 MINUTES-AC) Elon- Test gation temper- UTS, YS, percent Modulus, Treatment ature K.s.1 K.s.i. in p.s.i. X(x

l Welded plus 900 F.-2 hours-AC. 2 Welded plus 900 F.-4 hours-AC. 3 Welded plus 000 F.-8 hours-AC. 4 Welded plus 900 F.-16 hours-AC.

Another useful feature of the alloy of this invention is that aging at 1100 F. for S hours or more results in the (a.) Tensile properties as above stabilized Elongation percent in 2" Test UTS, YS, Mod- NTS, NTS/ temperature K s.i. K s.i. L U T ulus K s.i. UTS

(b) Following creep exposure Creep exposure Subsequent tensile properties Tern Elon- Modpera- Percent gation ulus ture, Stress, Time, defor- UTS, YS, percent p.s.i F. K s.i.l hours mation K .s 1 K s.i. in 1" X10 60m-r" 93- 5 0.150 157 142 1e 15. o 500 0. 193 156 147 17 15. 1

12 See footnotes Table VI.

The mechanical properties of Ti-8Mo-8V-2Fe-3Al in the form of 1/z-inch plate are shown in the following Table IX. The alloy is readily air-hardenable at this gage. Similar results were obtained in .2 plate. The excellent notch properties and plane strain crack propagation resistance are inherent features of this alloy.

TABLE IX.MECHANICAL PROPERTIES OF 1/2 THICK PLATE OF Ti8Mo- SV-ZFeBAl Elon- RA gation Modulus UTS, YS, perpercent p.s.i. Heat-treatment K s.i. K s.i. cent in 1" X106 (a) Room temperature tensile test:

0 F.-1O minutes-AC 119 118 48 24 14. 1 116 114 53 27 12. 5 117 116 63 29 12. 2 1,500

16 hours-AC 210 197 4 4 16. 2 Do 210 7 4 16. 0 Do 209 195 9. 5 8 16. 3 (b) 600 F. s

1,500 F.10 minutes-AC plus 900 F.-

16 hours-AC 161 143 54 4 12. 6 Do 181 159 16 7 13. 2 179 157 16 4 13. 9

(c) RT notch tensile: Kt value NTS Average 1,500 1?.-10 minutes-AC plus 900 F.

16 hours-AC 2. 8 262 D0..- 2. 8 263 263 D 2. 8 263 1,500 I". minu es-AC plus 900 F.-

8 hours-AC 8 233 D0". 8 223 226 D0 8 223 1,500 F. minu esAC plus 900 Fr- 16 hours-AC 8 230 D0... 8 227 229 Do. 8 231 (d) 600 I". notel ensile:

1,500 F.10 minutes-AC plus 900 Fr- 16 hours-AC 2. 8 234 0... 2. 8 244 241 Do 2. 8 246 1,500 F.-10 minutes-AC plus 900 F.

8 hours-AG 8 231 (e) Kia value 1,500

16 hours-AC Ti-8Mo-8V-2Fe-,3Alalso possesses good forming characteristics with `a minimum bend radius in the solution treated condition of 2T and 3T when stabilized. As shown in Table I, it possesses good uniform elongation, and a low annealed yield strength, which would enable forming of larger parts to be done, or use of smaller presses for equivalent parts.

In summary, it is claimed that the alloy of this invention, Ti-8Mo-V-2Fe-3Al, is superior to the present commercial alloy Til3V-llCr3Al in the following respects: Speed and control of aging, notch tensile strength, notched fatigue strength, stress corrosion resistance and weldability.

Alloys according to the invention may be produced by admixing titanium sponge with the alloying ingredients in comminuted orm, compacting the admixture into a consumable electrode and arc melting in a cold mold furnace such as a water-cooled copper crucible to produce an ingot of the alloy. Homogeneity of the ingot may be improved by utilizing the ingot as such as a consumable electrode and arc-remelting into a cold mold Crucible of larger diameter than the irst.

For breakdown operation the resulting ingot is heated to about 1860 F. and rolled or forged to a desired shape.

What is claimed is:

1. A titanium base alloy consisting essentially of about: 7 to 9% each of molybdenum and vanadium, .1.5 to 2.75% iron, 2.5 to 3.5% aluminum, up to 0.2% in total amount of carbon, oxygen and nitrogen, balance titanium, characterized in being substantially immune to stress corrosion cracking, in being age hardenable to a yield strength of about 180,000 p.s.i. on solution treating and thereafter aging at about 900 F. for about 8 hours, andlin having a tensile elongation of at least 5% in the aged condition.

2. An alloy according to claim 1 containing about: 8% each of molybdenum and vanadium, 2% iron and 3% aluminum.

3. A wrought article made of an alloy according to claim 1.

4. A wrought and solution-treated article made of an alloy according to claim 1 characterized by an 0.2% offset yield strength .of not more than about 120,000 p.s.i. and a tensile elongation of at least 10%.

5. An age-hardened titanium-base alloy according to claim 1 characterized by an 0.2% offset yield strength of at least 180,000 p.s.i. and a tensile elongation of at least 5% References Cited UNITED STATES PATENTS 2,754,203 7/ 1956 Vordahl 75-1755 2,918,367 12/1959 Crossley et al. 75175.5 3,306,739 2/ 1967 Evans et al. 75-175.5 3,405,016 lO/1968 Jaiee et al 148--133 FOREIGN PATENTS 659,577 3/ 1963 Canada.

776,440 6/ 1957 Great Britain.

782,564 9'/ 1957 Great Britain.

CHARLES N. LOVELL, Primary Examiner U.S. Cl. X.R. 14S-32.5, 133

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