US3482968A - Titanium base alloys of high strength at atmospheric and elevated temperatures - Google Patents

Description

United States Patent TITANIUM BASE ALLOYS OF HIGH STRENGTH AT ATMOSPHERIC AND ELEVATED TEMPERATURES Donald B. Hunter, Henderson, Nev., assignor to Titanium Metals Corporation of America, New York, N.Y., a

corporation of Delaware No Drawing. Filed Aug. 8, 1967, Ser. No. 659,027

Int. Cl. C22c 15/00 US. Cl. 75-1755 7 Claims ABSTRACT OF THE DISCLOSURE An age hardenable titanium base alloy consisting essentially of about 7% aluminum, 14% tin, 25% zirconium, 15% tungsten, up to 0.5% in total amount of carbon, oxygen and nitrogen, balance titanium apart from impurities within commercial tolerances, characterized by high strength and ductility at room and elevated temperatures and high creep stren th at temperatures up to about 1100 F.

This invention relates to titanium base alloys which contain tungsten as an essential component, and which are characterized by high elevated temperature strength, thermal stress stability, good notch properties and good creep resistance. These properties are particularly desirable in the construction of modern high speed jet engine parts. The invention also relates to the processing of these alloys in a manner which serves to maximize their desired characteristics.

Titanium, because of its low density and high melting point is well adapted to high temperature structural applications in aircraft and the like. The pure metal alone, however, does not possess suflicient strength for most applications; and it must be alloyed with other metals in order to overcome this deficiency. Aluminum can be alloyed with titanium to provide increased strength; however the amount of aluminum must be kept below about 8% in order to preserve the ductility of the material. Tin, zirconium and molybdenum also add to the strength of Patented Dec. 9, 1969 temperatures, it does present other problems. The element silicon has a tendency to segregate during melting. Also, even small amounts of this element produce severe embrittlement of the titanium base alloy.

The present invention makes use of the discovery that silicon may be omitted entirely in titanium base alloys through the substitution of tungsten for molybdenum. It has been discovered that by virtue of this substitution, it becomes possible to fabricate a titanium base alloy which has high temperature creep resistance, strength and ductility.

The present invention makes possible the elimination of silicon in titanium base alloys without the attendant loss of creep resistance at high temperatures. Moreover, ductility and strength are preserved and have been found to be at least equal to any known titanium alloy. These advantages are achieved through the substitution of tungsten for molybdenum and the elimination of silicon.

It has further been discovered that by forging, rolling or subsequently annealing the metal above its beta transus temperature (i.e. above about 1885 R), an exceptional combination of strength, creep resistance, notch toughness and termal stability, not found in any presently available titanium base alloys, can be achieved.

The alloy of the present invention consists essentially of about 5 to 7% aluminum, 1 to 4% tin, 2 to 5% zirconium, 1 to 4% tungsten, up to 0.5% in total amount of carbon, oxygen and nitrogen, but preferably not to exceed 0.1% nitrogen and 0.2% carbon, balance titanium, apart from impurities within commercial tolerances.

A preferred alloy according to the invention is Ti-6Al-2Sn-4Zr-2W. Another preferred alloy is For purposes of comparing properties of alloys according to the invention with closely related compositions containing silicon, compositions were melted in accordance with the following Table I, forged specimens of which were tested in various heat treated conditions and with results and as shown in the succeeding table hereof. Table I gives both the nominal and actual composition of the various alloys melted and tested.

TABLE I.ANALYSIS OF INGOTS Per- Per- Per- Per- Per- Per- Per- Per- Percent cent cent cent cent cent cent cent cent Denisty, Beta Ingot No. Nominal Composition Al Sn Zr W 0 Fe N C v lbs/cu. in. Transu V-3072 Ti-(iAl-2Sn-4Zr-2W 5. 93 2. 05 4. 05 2.08 0.115 0. 046 0.011 0. 28 0. 165 1,8751,900 V-3428 Ti-6Al-2Sn-4Zr-2W 5.98 1.98 3.82 2. 03 0.130 0.062 0.007 V-3239 Ti-6Al-2Sn-4Zr4W 5. 96 2. l3 3. 4. 38 0.134 0.078 0. 004 V-3418 Ti-6Al-5Zr-lW-02Si 5. 98 5. 01 1.01 0.103 0.125 0. 004 0. 209 0. 162 2 1, 875 V-300l Ti-6Al-2Sn-4Zr-2Mo-0.253i 5 98 2.12 4. 07 3 1. 99 0.076 0. 049 0. 006 0.29

I Accurate beta transus determination handicapped by segregation in ingot.

2 Manuiaeturers figure.

3 M0 the material; and it has been found that a composition Ti-6Al-2Sn-4Zr-2Mo provides an excellent combination of strength, notch toughness and weldability. In order to achieve acceptable creep resistance in the temperature range of l000-1100 F. however, there must be added an amount of silicon up to about 0.25%.

While the presence of silicon in a titanium base alloy serves to improve creep resistance, particularly at higher Table II shows the room and elevated temperature tensile properties for the Ti-6Al-2Sn-4Zr-2W alloy in the various heat treated conditions shown. The heat treatments include sub-beta transus solution treatment followed by air cooling and aging. It will be observed that aged ultimate and 0.2% offset yield strengths up to ISO-K s.i. are obtained with excellent ductilities both as regards tensile elongation and area reduction values.

TABLE IV.ROOMI TEMPERATURE NOTGH PROPERTIES OF Tl-6Al-2Sn-4Zr-2W l Heat treatment Ingot No.2 72

Notch Notch time Fracture Notch Impact configutensile resistration, strength, ance, Kt Passed, K p.s.i. Failed, K p.s.i. K p.s.i. 1t./lbs.

2. 8 5 hrs. at 210--. 28 mins. at 220 230 9. O 2.8 do 27 mins. at 220.-. 233 9. 25 2.8 5 hrs. at 220 Broke loading at 230 238 9. 5 2. 8 5 hrs. at 200 4 hrs. 4 mins. at 210 237 12. 5 3. 8 do 1 min. at 210 3.8 do 4 mins. at 210 5 hrs. at 190..- Broke loading at 200.

,825 F.-% hr.-AC plus 1,100 F.-8 hrs-AC.

5 hrs. at 180..- 12 mins. at 190.--

l Processed below beta transus.

With a notch configuration of K =8, the alloy withstood at 5 hours at 180K p.s.i. Decreasing the severity of the notch to K =3.8 enabled the alloy to withstand 5 hours at 200K p.s.i. With the sharper notch configuration of K =8, the notch tensile strength was over 200K p.s.i. while with a K =3.8, the notch tensile strength rose to 220K p.s.i.; and with a K,=2.8 the notch tensile strength rose to 230K p.s.i. Impact resistance was around 9 ft.lbs. This compares Wtih an impact resistance of 20-25 ft.-lbs. for Ti-6Al-2Sn-4Zr-2Mo with similar section sizes and heat treats.

The beta transus of Ti-6Al-2S-n-4Zr-2W is about 1885 F. NASA sharp notch properties of this alloy (Le. Ingot No. 3428) after being processed and solution treated below the beta transus, are shown in Table V.

Table V demonstrates that the sharp notch values decrease with increase in aging time at 1100" F. On the other hand, Table V also shows that increasing the solution temperature tends to raise NASA sharp notch values for each aging time. Thus, with samples aged for 24 hours at 1100 F., increasing the solution temperature from 1675 F. to 1775 F., and then to 1825 F., raised the sharp notch values from 113 to 115, and then to 118. This demonstrates that employment of higher solution temperatures may be expected to improve the NASA sharp notch performance of Ti-6ALZSn-4Zr-2W.

The creep stability properties of Ti-6Al-2Sn-4Zr-2W (i.e. Ingots Nos. V-3072 and V-3428) processed and solution treated below the beta transus, are given in Table VI.

Solution Treated at 1,675 F.

Solution Treated at 1,775 F. Solution Treated at 1,825 F.

Aging Aging Aging t e, NASA, time, NASA, time, NASA, hours NTS Average hours N TS Average hours N TS Average TABLE VIx-CREEP STABILITY PROPERTIES OF Ti-6Al-2Sn-4Zr-2W Creep Exposure Subsequent Tensile Properties Percent Temp, Stress, Time, defor- UTS, Y RA, Elong., Modulus Ingot N 0. Heat treatment F. K p.s.i. hours mation K p.s.i. K p.s.i. percent percent EXlO-"ps i.

V-3072 .1 1,675.-% hr-AC plus 1,100 F.-8 hrs-AC 800 70 150 0. 091 159 152 37 21 16.6 V-3072 1,675 D.-% l11.-AC plus 1,100 F.-8 hrs-AC- 1,000 30 150 0. 194 157 148 34 18 16. 7 V-3072 1,675 F.-% h1'.-AO plus 1,100 F.-8 hrs-AC 1,000 30 150 0.373 157 31 18 17. 2 V3072 1,675 F.-% hr.-AO plus 1,100 F.- 8 hrs-AC 1,100 15 0.924 146 30 16 16. 3 V3072. 1,675 F.-% hr.-AC plus 1,100 F.-8l1rs.-AC 1,100 15 150 2. 303 161 154 26 13 17. 0 V3072- 1,675 F.-} hr.-AC plus 1,100 F.-8 bra-AC 1, 100 15 150 1. 386 161 154 27 12 18. 5 V3072 1,675 F.-% hr.-AC plus 1,100 F.-8h1s.-AC 1, 100 18 150 0.416 159 150 19 16 Z 16. 3 V3072 1,675 F.-% 111.-AC plus 1,100 F.-8 hrs-AG -1- 1, 100 18 150 0. 550 163 150 24 16 2 17. 2 V3072 1,650 F.-1 hr.-AO plus 1,100 F.-8 hrs-AC 1, 100 15 150 0.957 155 147 34 16 17.9 V3072 1,650 F.-1 hr.-AO plus 1,100 F.-8 hrs-AC 1,100 15 150 1. 261 155 146 28 16 17. 2 V3072 1,650 F.-1 hr.-AC plus 1,100 F.-8 hrs-AC 1,100 18 150 1. 902 155 145 34 16 16. 5 V-3072- 1,650 F-l hr.-AO plus 1,100 F.- 8 hrs.-AC. 1,100 18 150 1. 199 154 146 33 16 15. 7 V-3072 1,775 F.-% hr.-AC plus 1,100 F.-8 hrs-AC 800 70 150 0.133 153 148 38 21 15. 4 V3072 1,775 F.-% hr.-AC plus 1,100 F.-8 hrs-AC 1,000 30 150 0. 290 154 27 17 16. 8 V3072 1,775 F.-% hr.-AC plus 1,100 F.- 8 hrs-AC 1,000 30 150 0. 278 158 152 30 18 16.7 V3072 1,775 F.-V hr.-AC plus 1,100 F.-8 hrs-AC 1, 100 15 150 1.077 157 152 12 8 15. 5 V3072 1,775 F.-% 11r.-AO plus 1,100 F.-8 hrs-AC 1, 100 18 150 0. 814 157 24 14 16. 5 V3072 1,825 F.-% hr.-AC plus 1,100 F.-8 hrs-AC 800 70 150 0. 117 152 147 40 17 16. 1 V3072 1,825 F.-% hr.-AC plus 1,100 F.-8 hrs-AC 800 70 150 0.095 154 148 34 17 18. 3 V-3072 1,825 F.-% hr.-AC plus 1,100 F.-8 hrs.- AC 900 50 150 0. 220 156 149 39 19 17. 4 V-3072- 1,825 F.-% hr.-AC plus 1,100 F.-8 hrs-AC 900 50 150 0. 213 152 145 40 17 16. 2

See footnote at end of table.

F.-1100 F. This is the Modulus RA, Elng., EX- percent percent p.s.i.

10 exposure, the amount of deformation was also about 0.1%

stance similar to Ti-SAl-SSn-SZr over the entire temperature range of 800 UTS, YS,

As shown in Table VII for either beta annealing or Beta processed or beta annealed Ti-6Al-2Sn-4Zr-2W thus .i. Also, the elastic modulus of the samples has a creep resi d by the beta treatment to the range of 17.5-

5 only alpha-beta alloy known to possess this quality. The ductility of the beta processed samples was good, Table VIII shows the results of increasing the tungsten content of the alloy of the present invention to a nominal value of 4% (i.e. Ingot No. V-3239).

TABLE VIIL-SOME PROPERTIES OF T-6Al-2Sn-4Z14W, V-3239 0 E Test reep xposure Percent temp, Temp, Stress, Time, Defor- F. F. K p.s.i. hours mation K p.s.i. K p.s.i.

1 Creep deformation figures are average of two, except for figures marked which are single values. 2 K p.s.i. load.

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was increase x 10" psi.

with the samples undergoing around 30% reduction in cross section area (RA).

Heat treatment Table IX shows that at room temperature the 0.2% offset yield strength of the alloy of the present invention is somewhat greater than that of the silicon con taining alloys. However, at increased temperatures, the alloy of the present invention exhibited much greater yield strengths than the silicon containing alloy which also contained tungsten; and while at the higher temperatures its yield strength was slightly below the other silicon containing alloy, its notch strength and creep resistance very greatly exceeded that of both silicon containing alloys.

The NASA Sharp Notch Values for the silicon free alloy of the present invention ranged between 110 and 102 when aged for dilferent lengths of time at 1100 F. The NASA Sharp Notch Values for the silicon containing alloys, on the other hand, ranged between 71 and 100 for corresponding aging times and temperatures.

The creep resistance of the alloy of the present invention at elevated temperatures was far superior to the silicon containing alloys; and at 1100 F. the alloy of the present invention exhibited less than half the creep undergone by the silicon containing alloys under the same loads and durations.

It will be appreciated that the alloy of the present invention provides a combination of tensile strength, creep resistance, toughness and ductility at elevated temperatures which is unmatched by any other previously known alloy. Moreover, the improved mechanical properties of the alloy of the present invention are sharply enhanced when the alloy is either processed or annealed above its beta transus temperature.

What is claimed is:

1. An age hardenable titanium base alloy consisting essentially of about: 57% aluminum, 14% tin, 2-5% zirconium, 1-4% tungsten, up to 0.5% in total amount of carbon, oxygen and nitrogen, balance titanium apart from impurities within commercial tolerances, characterized by high strength and ductility at room and elevated temperatures and high creep strength at elevated temperatures up to about 1100 F.

2. A titanium base alloy as in claim 1 wherein tungsten is present in the amount of about 2%.

3. A titanium base alloy as in claim 1 wherein tungsten is present in the amount of about 4%.

4. An age hardened alloy according to claim 1 having an ultimate strength of at least 150K p.s.i. and a tensile elongation of at least 10%.

5. An alloy according to claim 1 containing about 6% aluminum, 2% tin, 4% zirconium and 2 to 4% tungsten.

6. An alloy according to claim 1 containing about 6% aluminum, 2% tin, 4% zirconium and 2% tungsten.

7. An alloy according to claim 1 containing about 6% aluminum, 2% tin, 4% zirconium and 4% tungsten.

References Cited UNITED STATES PATENTS 2,769,707 11/1956 Vordahl 75-1755 3,049,425 8/ 1962 Fentiman et al 75-175.5 3,105,759 10/ 1963 Fentiman et a1 75175.5 3,378,368 4/1968 Minton et al. 75-1755 FOREIGN PATENTS 949,841 2/1964 Great Britain.

CHARLES N. LOVELL, Primary Examiner U.S. C1. X.R. l4812.7, 32.5