US3105759A

US3105759A - Titanium-base alloys

Info

Publication number: US3105759A
Application number: US852491A
Authority: US
Inventors: Fentiman William Percival; Morton Peter Harlow; Ames Stuart Leslie; Marsden Terence Barclay
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1958-11-14
Filing date: 1959-11-12
Publication date: 1963-10-01
Anticipated expiration: 1980-10-01
Also published as: CH405722A; BE584616A; US3049425A; DE1291512B

Description

United .States Patent 3,105,759 TITANIUM-BASE ALLGYS William Percival Fentiman and Peter Harlow Morton, Birmingham, England, Stuart Leslie Ames, Natrona Heights, Pa., and Terence Barclay Marsden, Sutton Coldeld, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Nov. 12, 1959, Ser. No. 852,491 Claims priority, application Great Britain Nov. 14, 1953 4 Claims. (Cl. 75-1755) This invention is concerned with .titanium-base alloys which have high temperature creep strength and which do not undergo embrittlement during use at high temperature.

Alloys for use in certain elevated temperature applications where dimensional stability is important, such as gas turbine compressor blades, require to have good creep properties, together with adequate strength and freedom from embrittlement during service. It -is desirable that an alloy for use in such applications should possess as many as possible of the following properties: high room temperature ultimate strength and adequate ductility, high strength and low creep rates at temperatures of 400 C. or more, freedom from embrittlement, high tolerance for hydrogen, good forgeab-ility, low density and good oxidation resistance.

In this specication, all components are defined in terms of percent by weight.

Titanium-base alloys have been proposed for such applications since they have moderately low density and good oxidation resistance and certain alloys have good properties at elevated temperatures. One such alloy is that containing 13% tin and 2.75 aluminium which has good creep properties but suffers from the disadvantage that at certain levels of hydrogen content serious embrittlement at service temperatures is encountered which has rendered the alloy unsuitable for use in the abovementioned applications unless it is Vacuum annealed to reduce the hydrogen content. This is an expensive process and obviously adds to the cost of production.

We have found that by modifying the composition of titanium-tin-aluminium alloys good creep resistance without embrittlement at all levels of hydrogen content can be Vobtained when the alloys have been heat-treated.

An object of the invention is to provide titanium-base alloys having good creep properties.

Another object of the invention is :to provide titaniumbase alloys with good creep properties which do not undergo embrittlement during use at high temperatures. A further object is a titanium-tin-aluminium alloy having good tolerance for hydrogen, the properties of which can be raised to higher levels by addition elements.

A still fur-ther object is a heat-treatment which, with modifications, can be applied to the alloys of the invention -to produce creep properties of a high order.

Other objects and advantages of the invention will become apparent from the detailed description thereof.

Titanium-base alloys having good creep properties which are free from embrittlement at elevated temperatures consist essentially of tin and aluminium, the tin ICC content and the aluminium content relative to that tin content being in the range 14% tin with 0.5% aluminium, 14% tin with 2.2% aluminium, 7% tin with 4.25% aluminium and 7% tin with 2.5% aluminium and O-0.5% silicon balance titanium and usual impurities.

A desirable range of composition is that in which the tin and aluminium contents are between the following limits: 13% tin with 1% aluminium, 13% tin with 2.5% aluminium, 9% tin with 2% aluminium, 9% tin with 3.6% valuminium and 00.5% silicon. The preferred range of composition is that in which the Itin and aluminium contents lare between the following limits: 12% tin with 1.75% aluminium, 12% tin with 2.75% aluminium, 10% tin with 2.75 aluminium and 10% tin with 1.75 aluminium and 0-0.5% silicon.

The ranges of composition of tin and aluminium content -are illustrated in the accompanying drawing in which:

Point A represents 14% tin, 0.5 aluminium,

Point B represents 14% tin, 2.2% aluminium,

Point C represents 7% tin, 4.25% aluminium,

Point D represents 7% tin, 2.5% aluminium,

Point L represents 13% tin, 1% aluminium,

Point M represents 13% tin, 2.5 aluminium,

Point N represents 9% tin, 3.6% aluminium,

Point O represents 9% tin, 2% aluminium,

Point P represents 12% tin, 1.75% aluminium,

Point Q represents 12% tin, 2.75% aluminium,

Point R represents 10% tin, 2.75 aluminium and Point S represents 10% tin, 1.75% aluminium.

The usual impurities found in titanium-base alloys linclude carbon, oxygen, nitrogen, hydrogen and iron and it is desirable that the amounts of such elements should be kept as low as possible.

In the following description relating to various compositions of alloys, in many instances no reference is made to the titanium content, but it is to be understood that :the remainder of the composition is titanium and usual impurities.

The line BC of the FIGURE represents the limit of composition of alloys having elongation values of not less than 10% on 4\/; with a hydrogen content of up to 180 parts per million, determined on specimens heattreated 30 minutes at ll00 C. air cooled, reheated to 800 C. and furnace cooled. Alloys having compositions on the left of the line BC have at all commercial hydrogen levels been found to be free from embrittlement after heat-treating to produce the best creep properties. On the right of the line, the amount of hydrogen present in the alloy aifects the tendency to become embrittled and the further the composition from the line the smaller is the amount of hydrogen that can be tolerated.

This decrease in the tolerable hydrogen content with increasing alloy content is rapid and the line XY represents the limit of composition of alloys having elongation values of not less than 10% when the hydrogen content does not exceed 10 parts per million. It will be seen that the `difference in composition between alloys on the limit BC and alloys on the limit XY is small and Y Patented Oct. 1, 1963 have all the beneficial properties possessed by the alloys whose compositions fall within the area. Thus, whilst certain of the alloys outside the area may have, for example, good ductility, they may be rather weak or have poor forgeability or, on the other hand, they may have good tensile strength but rather high creep rate or may suffer embrittlement.

We have found that the best creep properties in the alpha-type ternary titanium-tin-aluminium alloys in accordance with the invention are associated with an acicular type of structure and such a structure may be produced by heat-treatments. The alloys are heated to a temperature in the beta tield, cooled and reheated in the upper part of lthe alpha field, the rate of cooling from the 'beta field determining the properties. Slow cooling, as -by air cooling gives a low creep rate at 500 C. whilst fast cooling as -by quenching into Water gives a stronger material with a moderately higher creep rate. A heat-treatment which has been found to give satisfactory results is to heat the alloy to a temperature of 1100 C., air cool or quench to room temperature and reheat to 700 C. or 800 C. for a period and air cool in the furnace -to room temperature. When air cooled, the alloy is allowed to cool at a natural rate in free air and when furnace cooled the alloy cools at the rate at which the furnace cools when closed and the heating source turned off.

Table I shows the tensile properties of a number of titanium-tin-aluminium alloys outside the range of alloys in 4accordance with the invention. All the examples contained about 180 parts per million of hydrogen and had been heated to 1100 C. for 30 minutes and air cooled and then reheated to 80.0 C. -for 1 hour and furnace cooled. The elongation of most of the alloys is below which is the minimum acceptable ductility value. Of those alloys which have acceptable elongation figures the maiority have lower strength than the alloys of the invention.

In Table II are given the tensile properties of alloys which fall within the range of composition in accordance with lthe invention yand of alloys which are near that range and which have been treated and tested in the same manner as those in Table Il. It will be seen that there is a marked fallin ductility of alloys which are on the right of the line BC of the ligure, these alloys being outside the range. The strength and ductilty of ,all the alloys falling within t-he range are good. Creep strength is related to the total content of tin `and aluminium and those alloys at the lower end of the range have lower creep strength than those at the upper end. In general, alloys containing less than 8% tin have more limited applications than those containing more than `8% tin but ductility is good, e.g. an alloy containing 7.7% tin and 3.1% aluminium has, after heat-treatment, elongation and reduction in area values.

The area LMNO of the figure represents compositions in which a total plastic strain of about 0.1% or less is produced when creep tested .at 400 C. under a stress of 25 tons/sq. in. over a period of 300 hours after quenching from 1100 C. and annealing at 800 C. followed by air cooling. Table III shows the total plastic strain values obtained from alloys which fall within the area. Of the compositions which fall within the area LMNO of the ligure, the best combination of properties is found in the alloy containing 11% tin and 2.25% aluminium. This alloy has good creep properties and is free from the occurrence of embrittlement during service. Whilst the creep properties of this alloy are not quite las good as alloys containing higher percentages of tin and aluminum, such -as the 13% tin, 2.75% aluminium alloy, the ductility of the 11% tin, 2.75% aluminium during service is a considerable improvement on the known alloys. The tendency to become embrittled in service can be determined by carrying out tensile testsvv on heat-treated specimens which have been subjected to creep testing. In such a determination the ductilityof the 13% tin, 2.75 aluminium alloy as shown by elongation and reduction in area values fell to about 7% in each case whereas, in the case of the 11% tin, 2.25% aluminium alloy, the elongation and reduction in area values did Anot fall below 13% and 27% respectively at similar levels of hydrogen content.

For production purposes a suitable range of composition for the 11% tin, 2.25% aluminium alloy is 10.5% to 11.5% tin and 2%-2.5% aluminium.

In the figure the line FG marks the limit of good forgeability at 1000" C. Compositions on the left of the line have good forgeability and such compositions include almost all the alloys of `the invention. Alloys on the right of the line are forgeable but rather more care is required than with alloys on the left.

It will be evident from the foregoing consideration ofVV the properties of titanium-tin-aluminium alloys in accordance with the invention that such alloys are an improvement over previously known titanium-tin-aluminium alloys in that, in the alloys of the invention, in particular the 11% tin, 2.25% aluminium alloy, are combined good tensile properties, good creep properties at a temperature of 400 C., freedom from embrittlernent, high tolerance for hydrogen, good forgea'bility, good oxidation resistance and moderate density. It will also be evident that all such properties are not found in all titanium-tin-aluminum alloys but an excellent combination of all or most of these desirable properties is found in the comparatively small range of composition represented by the alloys of the invention.

The creep properties of the ternary alloys can tbe further improved by the addition of one or more alloying ele-` ments. The preferred elements are: zirconium 1-l0%,

-silicon 0.05-0.5% Aand copper 0.12.5%, of which zirconium is Ian alpha stabiliser and silicon :and copper are beta stabilisers which may form metallic compounds in some conditions of heat-treatment. Examples of the improvement in properties are shown in Table IV which summarizes creep tests `at 25 tons/sq. in. at 400 C. made on alloys heat-treated 15 mins. at 1100 C. air cooled and 1 hour at 700 C. and furnace cooled. It will be apparent that a reduction of plastic strain results from the inclu-f sion of lalloying elements in the ternary alloy.

. In those alloysin which the alloying addition is zir-l conium the 10% -addition gives higher room temperature strength 'and better creep properties at 400 C. than the 5% zirconium alloy. The 5% zirconium alloy gives better creep properties at 500 C. than the 10% zirconium alloy Iand is also more readily forged. In a comparative ktest in which the test pieces were heat-treated at l100 C. `and 700 C. as before described and creep tested at 500 C. under a load of 15 tons/sq. in. for 300 lhours, the 11% r particular purposes and a zirconium content of about 10% in alloys for other purposes. A desirable range of composition in one case, is therefore, 21/2 to 71/2 zirconium and a suitable range covering permissible variation of composition on a production scale is 4 to 6% zirconium. In the other case, a desirablerange of composition is,

therefore, 6 to 10% zirconium and a suit-able range covering permissible variation of composition on fa production scale lis 8 to 10% zirconium. Since zirconium is an alpha stabiliser such alloys are of the alpha type. f

'Ilhe creep properties of alloys in accordance with the invention are to a great extent dependent upon heattreatment and the effects of various heat-treatments on the 11% tin, 2.25% aluminium, 5% zirconium alloy creep tested at 500 C. under a stress of l5 tons/sq. in. are ygiven in Table V. In order to obtain the best creep properties, the alloy must be heated to a temperature above 950 C. and whilst 975 C. `or 1l00 C. can be used, preferably the temperature of solution treatment is 1000 C. followed by air cooling and reheating to 700 C. and air cooling. The double heat-treatment involving solution treatment and ageing has the effect of lowering the plastic strain compared with the single heat-treatment.

A comparison of the 11% tin, 2.25 aluminium, 5% zirconium alloy with other well known alloys is made in Table VI in which `are given the stress values required to produce 0.1% total plastic strain in 300 hours -at various temperatures. Whilst certain of the lalloys 'require higher stress to produce the specified strain at 300 C. and 400 C., the superiority of the alloy in accordance with the invention at higher temperatures-is evident.

Silicon may optionally be -added to the 11% tin, 2.25% aluminium, 5 zirconium alloy to produce ian increase in tensile strength with only a slight fall in ductility.

The most beneficial effect of silicon is in improvement in total plastic stra-in `after heat-treatments involving heating in the beta field at temperatures of 975 C. or more, air cooling and ageing at temperatures in the range 500 C. to 700 C. In one condition of heat-treatment involving heating to 1000 C., air lcooling yand re-heating to 700 C. and air cooling the total plastic strain is reduced to 0.083% in 300 hours under tons/sq. in. at 500 C., Aand in another condition of heat-treatment involving heating to 1000 C. air cooling and reheating to 500 C., 'and air cooling, the total plastic strain under the same test conditions is reduced to 0.070%.

The improvements in the properties of the 11% tin, 2.25 aluminium, 5% zirconium alloy 'brought about by -silicon additions and by heat-treatment are shown in Tables VII, VIII Iand IX, the 0.2% silicon being the preferred addition. A useful range `of composition is .05%-0.3% silicon and on a production 'basis a suitable range for a nominal composition of 0.2% is 0.1%-0.25%.

Copper between 0.1% and 2.5% may be added to the 11% tin, 2.25% aluminium alloy lbut is notas effective as silicon in improving creep properties.

When added to the 11% tin, 2.25% aluminium, 5% -zirconium alloy, the copper additions should preferably be in the upper part of the range, ie. l%-2.5%, in order to obtain maximum benefit. Copper 'and silicon may be added together in the yalloys herein described in the amounts specified ffor single additions without loss of the benecial properties which result from the addition of either copper or silicon.

Additions of zirconium improve the elevated temperature tensile properties of titanium lalloys containing tin and aluminium 'and the extent `of the improvement can be seen in Table X which compares properties of the preferred ternary alloy composition with alloys having the same tin -and aluminium contents and containing varying amounts of zirconium and molybdenum .and tested at room and at two elevated temperatures.r All test-pieces Were heat-treated: l5 mins. at ll00 C., air cooled and reheated 1 hour at 700 C. and furnace cooled. An :addition of 1% molybdenum produces a similar effect on properties to 5% of zirconium yand it will be seen that strength and ductility yare very `good lat both 400 C. and 500 C.

Creep tests on the preferred ternary composition with the Iaddition of zirconium and molybdenum separately and together show that the additions are in gener-al particularly eifective -at a temperature of 400 C. in reducing total plastic strain whereas yat 500 C. there is a'greater amount of creep. The results of creep tests on such same as that in Table X.

When, in the fabrication or treatment of alpha-type and alpha plus beta-type alloys, it is necessary to heat them into the beta iield, there is in certain cases a loss of ductility particularly when measured by reduction in area and the alloys may have a coarse-grained fracture. Whilst the ductility can be restored by working the alloys in the alpha plus beta eld by considerable amounts, serious loss of ductility can be avoided by the addition of boron to the alloy.

lBoron can also be used to increase the strength of the alloys without loss of ductility and to reduce the total plastic strain under creep conditions particularly at temperatures around 400 C. Improvements in creep properties and strength resulting from addition of boron are illustrated in the results set out in Table XII in which specimens were heat-treated by air cooling from 1l00 C., reheated to 700 C. and furnace cooled. The range over which boron additions are effective in this respect is from 0.005% to 0.5% preferably 0.005 to 0.2%. The actual amount to be added depends upon the particular alloy but additions of the order of 0.025% have been found to be advantageous in many alloys. Alloys of the present invention may, therefore, be modified by the addition of boron within the above-mentioned ranges in order to avoid serious loss of ductility on heating into the beta eld. This is 0f importance in permitting forging to be carried out in the beta eld Without impairing ductility seriously.

The `outstanding creep properties described above depend in the first place on a titanium-tin-aluminium base which at -all commercial hydrogen contents has good creep properties and is inherently free from embrittlement. The addition elements raise the levels of the properties of the base but do not remove the embrittlement characteristics of a base which is inherently of low ductility under creep conditions. It is an important feature of the invention that by selecting appropriate compositions an -alloy may be produced having the optimum properties for the particular application envisaged having regard to the service temperature and stress involved.

Table l [Tensile properties of titanium-aluminium-tin alloys containing about 180 p.p.m. hydrogen after heat-treatment] Table II [Tensile properties of titanium-tin-eluminium allo Table V ,A [Creep properties 0f 11% Sn, 2.25% A1, 5% Zr alloy at 500 C. at 15 tons ys containing about 180 p.p .111. hydrogen after heat-treatment] sq. u1. after various heat treatments] Table VI l About.

Table IV [Creep properties at 25 tons/sq. in. at 400 1-Alloys heat-treated 15 Table VII [Effect of additions o silicon on creep and tensile properties of 11% Sn,`

% Zr-Heat-treatment 8 hours at 800 C mins. at 1100 C., air cooled, reheated 1 hour at 700 C. and furnace cooled] air cooled, creep Table VIII [Eiect of treatment on properties of 11% Sn, 2.25% Al, 5% Zr with and without 0.2% Si, creep tested at 25 tonslin.2 at 400 0.]

Table IX [Eicct o( Si contents of up to 0.4% on creep properties of 11% Sn, 2.25% Al, 5% Zr at 500 0.]

- Tensile properties after creep Percent testing Tons/in.a total Composition Treatment stress plastic strain in U. T. Percent Percent 300 hrs. t./in.2 on reduction l Aiw/Z area 11+2%+5 8 hours at 800 C. air cooled 15 0. 112 58. 3 18 37 11+2%+5+0.1% Si -do 15 0.206 60.8 18 38 11+2%|5+0.2% Si in 15 0. 202 61. 8 Y 18 38 11+2%+5+0.4% SL..- do 15 0. 300 66. 4 -13 34 11+2%+5 l hour at 1,000 C. air cooled and 1 hour at 700 C. 20 0. 144 60. 3 16 27 furnace cooled. Y 11+2%+5+0.1%Si do 20 0.111 63.3 13 20 11|2%+5+0.2% S1 do 20 0.083 65. 9 11 17 11+2%+5+0.4% SL..- d0 20 0. 110 67. 4 16 30 11+2%-|5 1 hour at 1,000 C. air cooled and 24 hours at 20 0. 136

550 C. air cooled. 11+2%+5l0.2% Si do 20 0. 080 11+2%+5 1 hour at 1,000 C. air cooled and 24 hours at 20 0. 160

500 C. air cooled. 11-|2%+5+0.2% Si do 20 0. 070

Table X [Effect of Mo and Zr on elevated temperature tensile properties of Ti, 11% Sn, 2% A1 heat treated 15 mins. at

1100 C., air cooled, and 1 hour at 700 C., furnace coole Limit of 0.05% proof Percent Percent Composition Test proportionstress tons/ U.T.S., on reduction temp., C. ality, tons/ in 2 t./i11.2 in area in z 4 M 11 Sn plus 2% A1 20 44. 5 48. 7 55. 4 12 27 ll Sn plus 2% Al plus 1 Mo. 2O 43. 7 48. 3 59. 5 9 17 11 Sn plus 2% A1 plus 2 Mo- 20 50. 0 53. 2 61.6 4 6 11 Sn plus 2% A1 plus 5 Zr..- 20 49. 3 54. 9 65.0 16 31 11 Sn plus 2% A1 plus 10 Zr 20 50. 9 54. 9 64. 4 10 14 11 S11 plus 2% A I.. v 400 17. 6 21. 1 30. 9 18 35 1l Sn plus 2% Al plus 1 Mo. 400 22. 3 27. 6 40. 1 18 53 11 S11 plus 2% Al plus 2 M0. 400 27. 2 34. 4 47. 2 14 21 11 Sn plus 2% Al plus 5 Zr 400 23. 7 27. 4 39. 7 19 30 11 S11 plus 2% Al plus 10 Z 400 28. 8 33. 5 47. 9 13 26 11 Sn plus 2% A1 500 16. 5 20. 5 28. 8 18 31 11 Sn plus 2% Al plus 1 500 21. 6 25. 9 37. 2 21 68 11 Sn plus 2% Al plus 2 M 500 28. 2 32. 6 44. 5 12 1l Sn plus 2% Al plus 5 Zr 500 21. 8 25.4 37. 5 19 42 11 Sn plus 2% A1 plus 10 Zr. 500 25.4 29. 6 43. 7 14 28 Table XI [Creep properties at 400 C. and 500 C. o! Ti, 11% Sn, 2%% Al containing Mo and Zr, heat treated] Tensile properties after creep Percent 0.01% prooi testing total stress at Composition Test conditions plastic test temstrain in perature U.T.S., Percent Percent 300 hours t./in. 2 el. on 4/A reduction m area 11 Sn plus 2% A1 plus 5 Zr 35 tons/in.2 at 400 C 2. 196 21.8 60. 5 14 15 1l Sn plus 2% A1 plus 10 Zr -do 0. 200 31.2 68.4 10 12 11 Sn plus 2% Al plus 2 Mn do- 0. 415 30.1 66.5 8 10 l1 Sn plus 2% A1 plus 5 Zr plus Mo do 04 234 27.7 62. 4 12 15 11 Sn plus 2% Al plus 5 Zr plus 1 Mo .do 0. 096 35 68. 9 9 10 11 Sn plus 2% A1 plus 5 Zr 15 tons/in.2 at 500 0-... 0. 049 15 62. 2 15 23 11 Sn plus 2% A1 plus 10 Zrdo 0. 080 15 66.0 15 19 11 Sn plus 2% Al plus 2 Mo 0. 398 15 70. 0 8 8 11 Sn plus 2% Al plus 5 Zr plus Mo- 0.132 15 65.9 7 10 11 Sn plus 2% A1 plus 5 Zr plus 1 Mo 0.202 15 69. 9 6 6 Table XII [Eieet of boron on creep and tensile properties of 11% Sui-254% Al+5% or 10% Zr with and without molybdenum] Temp Percent Percent Percent Composition percent Stress o C total plastic U.T.S. 61.0114@ reduction strain in area 11+2%+5 Zr 35 400 1. 424 62. 5 17 27 11+2%i5 Zr plus 0.025 B 35` 400 0. 784 (i44 4 18 31 11+2M+5 Zr plus 0.05 B-- 35 400 0. 674 62. 3 18 37 11-1-254-1-5 Zr plus 0.10 B-- 35 400 0. 479 63.5 15 35 11-1-2%+5 Zr plus 0.20 B 35 400 0. 300 15 32 11+2%+10 Zr 35 400 0. 265 64. 2 15 20 1l-l2%+10 Zr plus 0.025 B..- 35 400 0. 242 66. 4 15 15 11+2M+10 Zr plus 0.05 13---- 35 400 0.215 68. 5 14 24 11+2l4-l-10 Zr plus 0.10 13--..- 35 400 0. 186 n 70. 4 15 30 11+2%+10 Zr plus 0.20 B. 35 400 0.160 72. 0 16 25 1l+2%+5 Zr plus 0.5 Mo 15 500 0. 132 65. 9 7 10 11+2M+5 Zr plus 0.5 Mo plus 0.2 B 15 500 0.139 68. G 16 31 11+2%+5 Zr plus 1.0 Mo 35 400 0. 096 68. 4 10 12 ll+2%+5 Zr plus 1.0 Mo plus 0.025 B Y 35 400 0. 093 69. 3 13 23 N oren-All specimens heat-treated 1 hour at 1,100a C. air cooled and l hour at 700 C. furnace cooled.

We claim:

l. Titanium-base alloys having 10W creep rates at high temperature and high tolerance for hydrogen consisting essentially of tin and aluminum in the area defined by straight lines connecting the following four compositions in the ternary constitutional diagram of the titanium-tinaluminum system: 14% tin, 0.5% aluminum; 14% tin, 2.2% aluminum; 7% tin, 4.25% aluminum; 7% tin, 2.5% aluminum; `0.05%-0.5% silicon, 1%-10% zirconium, 0.005%-0.5% boron, balance titanium and usual impurities, said percentages being by weight.

2. A titanium-base alloy having low creep rates at high temperature and high tolerance for hydrogen consisting essentially of, by Weight, 10.5 %11.5% tin, 2.0%2.5% aluminum, 8%-10% zirconium, 0.1%-0.25% silicon, balance titanium and usual impurities.

3. An alloy consisting essentially of, by weight, 11% tin, 2.25% aluminum, 5% zirconium, 0.2% silicon, balance titanium and usual impurities, having an acicular type structure, less than 0.1% total plastic strain in 300 hours under a load of 25 tons per square inch at 400 C. and elongation of not less than 10% when exposed to hydrogen at a 'concentration greater than 10 parts per million.

4. A titanium-base alloy consisting essentially of by weight 10.5%-11.5% tin, 2.0%2.5% aluminum, 4%- 6% zirconium, 0.1%-0.25% silicon, balance titanium and usual impurities, having an acicular type structure, less than`0.1% total plastic strain in 300 hours under a load of 25 tons per square inch at 400 C. and an elongation of not less than 10% when exposed to hydrogen having a concentration greater than 10 parts per million.

References Cited in the ile of this patent UNITED STATES PATENTS 2,669,513 Ja'ee et al Feb. 16, 1954 2,779,677 Jaffee et al Jan. 29,; 1957 2,797,996 Jaee et al July 2, 1957 2,867,534 Jaiee et al. Ian. 6, 1959 2,892,705 Jafee yet al I une 30, 1959

Claims

1. TITANIUM-BASE ALLOYS HAVING LOW CREEP RATES AT HIGH TEMPERATURE AND HIGH TOLERANCE FOR HYDROGEN CONSISTING ESSENTIALLY OF TIN AND ALUMINUM IN THE AREA DEFINED BY STRAIGHT LINES CONNECTING THE FOLLOWING FOUR COMPOSITIONS IN THE TERNARY CONSTITUTIONAL DIAGRAM OF THE TITANIUM-TINALUMINUM SYSTEM: 14% TIN, 0.5% ALUMINUM; 14% TIN, 2.2% ALUMINUM; 7% TIN, 4.25% ALUMINUM; 7% TIN, 2.5% ALUMINUM; 0.05%-0.5% SLICON, 1%-10% ZIRCONIUM, 0.005%-0.5% BORON, BALANCE TITANIUM AND USUAL IMPURITIES, SAID PERCENTAGES BEING BY WEIGHT.