US2968586A

US2968586A - Wrought titanium base alpha-beta alloys of high creep strength and processing thereof

Info

Publication number: US2968586A
Application number: US761007A
Authority: US
Inventors: Milton B Vordahl
Original assignee: Crucible Steel Company of America
Current assignee: Crucible Steel Company of America
Priority date: 1958-09-15
Filing date: 1958-09-15
Publication date: 1961-01-17
Anticipated expiration: 1978-01-17
Also published as: GB916801A

Description

Jan. 17, 1961 M. B. voRDAl-u. 2,968,586

WROUGHT TITANIUM BASE ALPHA-BETA ALLOYS OF' HIGH CREEP STRENGTH AND PROCESSING THEREOF Flled Sept. 15, 1958 4 Sheets-Sheet 1 Jan. 17, 1961 M. B. voRDAHL 2,968,585

WROUGHT TITANIUM BASE ALPHA-BETA ALLOYS OF' HIGH CREEP 4 Sheets-Sheet 2 STRENGTH AND PROCESSING THEREOF Filed Sept. 15, 1958 www E EU n p U L n L l/ a @ce v/ LDQG. `Eran Y X5 i 1U@ .Qca E/G Mm /A/ VENTO/a ML TGA/5. VO/PDHI..

Jan. 17, 1961 DAHL 2, 8,586

M. B. voR 96 WROUGHT TITANIUM BASE ALPHA-BETA ALLOYS OF HIGH CREEP STRENGTH AND PROCESSING THEREOF Filed Sept. 15, 1958 4 Sheets-Sheet 4 /V/LTo/v B. V/PDAHL. By

Q4/MMM United States Patent` O `WROUGHTv TITANIUM `BASE ALPHABETA AL- LOYS '0F HIGH CREEP STRENGTH AND PROC- ESSING THEREF Milton B.'Vordahl, Beaver, Pa., assignor to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New Jersey Filed Sept. 15, 1958, Ser. No. 761,007 12 Claims. (Cl. 148-133) This invention pertains to heat treatable titanium-base alloys having at normal temperatures a mixed alpha beta microstructure and to heat treatments thereof which improve the creep strength of such alloys by distributing the high strength alpha phase in the sites at which much of normal creep deformation normally occurs, this distribution comprising a network and/or plate microstructure commonly termed a Widmanstatten microstructure, which is formed and strengthened as hereinafter described in accordance with the invention.

The mixed alpha-beta titanium-base alloys to which the invention is applicable are those containing about 2-15 atomic percent of one or more of the isomorphous and sluggishly eutectoid beta promoters, molybdenum, vanadium, columbium, tantalum, chromium, manganese and iron. The more rapidly eutectoid beta promoters may optionally be present in percentages by weight as follows, up to for tungsten, up to 5% in total amount for cobalt, nickel and copper, up to 2 to 3% for silicon and beryllium. For all such alloying additions to the unalloyed titanium-base metal, the lower effective limit is about 0.25%, except in the case of silicon and beryllium, the lower effective limits of which are about 0.1%.

Preferably present in these alloys is one or more of the alpha promoters, aluminum, tin and antimony, in percentages by weight up to about 10% for aluminum, 23% for tin and 18% for antimony, the lower effective limits of each of these elements being about 0.5%. The interstitials carbon, oxygen and nitrogen, preferably should not be present in total amount exceeding about 0.2%, although up to about 0.3% carbon, up to about 0.2% oxygen and up to about 0.1% nitrogen can be tolerated, these again being in percentages by weight.

'I'his application is a continuation-in-part of my applications Serial No. 132,327, i'lled December 1'0, 1949 (now abandoned); Serial No. 229,143, filed May 31, 1951; Serial No. 671,316, tiled July l1, 1957 (now Patent No. 2,857,269); and Serial No. 435,754, filed .Tune 10, 1954.

In my first three applications above referred to, I have described methods for imparting to titanium-base alloys having a mixed alpha-beta microstructure, optimum cornbinations of room temperature strength and ductility, and high ductility at any given strength level, said methods consisting essentially in subjecting such alloys to prolonged plastic deformation at temperatures within the mixed alpha-beta temperature range, i.e., at temperature below the beta transus temperature at which the microstructure of these alloys transforms on cooiing from an all-beta structure above the beta transus to a mixed alphabeta structure below the beta transus. As set forth in said applications, the preferred temperature range for carrying out said plastic deformation extends from about 400 C. or 750 F., up to about 50 C. or 100F.fbe-, ,A

low the beta transus temperature. As shown in said applications, the effect ofV plastically deforming ,such

mixed phase alloys within the two-phase temperature 2,968,586 Patented Jan. 17, 1961 field, is to impart thereto a microstructure comprising a coherent admixture or dispersion of small bodies of alpha titanium and of beta titanium, usually a globular intermixture of these two major phases. In my last mentioned application Serial No. 435,754, I have described various heat treatments applicable to these mixed phase, alpha-beta, titanium-base alloys for improving properties in various respects, including slow Acooling from above the beta transus for imparting `a structure having a good distribution of the alpha and beta phases, and subsequent quenching .from below the beta transus, in the range of about 50-400 F. below the beta transus and thereafter aging at about 750-1000 F. for improving room temperature mechanical properties of such alloys. As pointed out in said application, the subbeta-transusquenching and aging treatments, thus applied to these alloys as thus previously heat treated by slow cooling from above the beta transus to impart the aforesaid structure, produces a final heat treated structure having room temperature properties comparable to those obtained by plastic deformation in the alpha-beta temperature field as taught by my first mentioned applications, and thus provides a means of duplicating these properties without necessity for plastic deformation in the alpha-beta temperature field, as in the case ofrmassive forgings which cannot be satisfactorily worked in the two-phase field.

My further investigations have Ishown that whereas the processing and heat treatments of my applications aforesaid impart the best combinations of room temperature strength and ductility to these mixed alpha-beta alloys, they do not impart the maximum elevated temperature properties as regards hot creep .and stress rupture strength. The latter I now find to be attained with the network and/or plate or Widmanstatten structure resultingfrom working above the beta transus and slow cooling thence to below the beta transus. However, the Widmanstatten structure thus obtained must be equilibrated in composition by a relatively lon-g soak at a temperature high enough in the alpha-beta temperature field to give reasonable mobility and yet low enough to avoid effective agglomeration of the alpha. I find that within limits, a long time soak at lower temperatures is equivalent to shorter times at higher temperatures. A

Hereafter when the term equilibratingj equilibration or equilibrated is used, it means the purposeful step of soaking the alloy at elevated temperature below the beta transus and preferably in the range extending alpha-beta temperature range gives an alpha content which is much richer in aluminum than the beta. This alpha imparts high resistance to creep, and l find that if" it is so distributed as to interfere with the deformation of 'the beta to a maximum extent, then the entire structure has maximumA creep resistance. In this connection, I should point out that the distribution designed to resist creepis quitedifferent from that designed to resist slip." For creep resistance, ahigh aluminum content, relatively? lmassiv'e component is required to maintain its shape'and through being bonded tot-thebetarcomponent, to resistA change in shape .oftheentirestructure. `ln the case of creep, deformationis-- by way; offa huid-like drift of the,

mass by` indvidual'atOm movements (diffusion), fand. t massive barrersatefmtist effective. In the casehof slip,

the strains and irregularities produced by a much liner and more uniform distribution, is most effective in preventing the cataclysmic and complex sliding along plane surfaces. Y g

The development of a network and/or plate-like or Widmanstatten alpha distribution for providing high hot creep strength is accomplishedv by high temperature decomposition of thebeta phase. Slow cooling, isothermal treatment and -combinations of these are suitable. Extremely slow cooling from the beta temperature -eld causesr the beta phase to reject lalpha of near equilibrium composition-that is, alpha of highest possible aluminum content for `the aluminum-bearing heat treated alloys of the invention. Cooling slowly enough to accomplish this, however, gives an undesirably coarse or brittle structure. Intermediate cooling rates can be chosen to give networks andl Widmanstatten structures of any desired degree of neness, but the alpha is low in aluminum content and accordingly, a long time soak in the alpha-beta temperature field is desirable in order to raise it. On vthe other hand, this soak must lbe carried out at a low enough temperature to avoid effective agglomeration of the structure.

Appropriate cooling rates `for producing the Widmanstatten structure in cooling from above to below the beta transus ordinarily range from about 3f per minute to 30 F. per minute, the preferred cooling rate varying roughly in inverse rel-ation within these in accordancewith the beta content ofthe alloy. That is to say, for the alloys containing beta promoters at the lower limit of about 2 atomic percent, the highest cooling rate of about 30 F. per minute would be appropriate, the rate decreasing progressively asthe beta content increases so that at the upper limit of about 15 :atomic percent of beta promoters, the slowest cooling rate of about 3 F. per minute would be employed.

Widmanstatten structures in which all traces of work distribution of the phases have been destroyed are generally poor in room temperature ductility, and compromises may be required to secure a combination of relatively good hot creep properties and also fairly good room temperature properties. In accordance with this aspect, combinations of Widmanstatten and worked structures can be obtained by heating to some temperature below the beta transus instead of -to an al1-beta temperature. In addition, quenching from 'an intermediate tempera'ture below the beta transus followed by aging in accordance with the teachings of my application Serial No. 435,754 aforesaid, will strengthen the beta phase and give higher room temperature strength and higher short time hot strength than otherwise, all without completely destroying the basic Widmanstatten structure designed for hot creep strength.

In the accompanying drawings:

Fig. l is a macrostructure and Figs. 2 and 3 are macro structures of an Lalpha-beta alloy which has been worked above the `beta transus and slow cooled to impart the Vtidmanstatten structure having high creep strength.

Fig. 4 is a macrostructure, and Figs. 5 and 6 are microstructures of the same alloy as in Fig. l, which has, however, Ibeen plastically deformed in the alpha-beta temperature field to impart the ne grained equiaxed microstructure.

Figs. 710, inclusive, are graphical com-parsions of the 100 hour creep performance lat temperatures of 1000 F., 900 F., 800 F., and 600 F., respectively, of a mixedv alpha-beta alloy which has been processed to provide the Widmanstatten structure on the one hand as compared to the same alloy processed to provide, on the'other hand, the fine grained equiaxed microstructure resulting from plastic deformation in the alpha-beta temperature field. Fig. 11 is a microstructure of' another alpha-beta alloy which has been heat treated to impart the Widmanstatten microstructure, while Fig. 1'2 is a microstructure or" the same alloy as processed by plastic deformation in 4 the alpha-beta temperature field to provide the line equiaxed structure.

The `following Table I compares the room temperature and hot creep properties of typical alpha-beta alloys which have been previously worked in the alpha-beta temperature field to impart a tine grained equiaxed microstructure, 'as-"thereafter heat ltreated above the beta transus, on the one hand, lto impart 'the' Widmanstatten structure and high creep strength, and as heat treated, on the other hand, below the beta transus to impart optimum/room temperature tensile properties.

grained TABLE I y 24 hr. 800 F. Bend creep Treatment, and Room residual at 800 Alloy Temperature Microtensiles F. (a measure of long term creep str.), psi.,v

Ti-6Mo-2A1.. 1,700 F. furnace cool +1,475 F. 33,200

, Water quench +1,000 F. 8 hrs. (199-171-8-5-0) Widmanstatten structure. Ti-GOMo-ZAL.-. 1,400 F. water quench +900 F. 8 10,850

' hrs. (164-127-2030) Equiaxed alphabets. structure. Ti-Al-fiV 1,825 F. furnace cool 1,500 F. 41,000

Water quench +1,0,00` F. 8 hrs. (181-172-4-9) Widmanstatten structure. Ti6A14V 1,550 F. water quench +900 F. 8 36,000

hrs. (185-160-l2-27-5) Equiaxed alpha-beta structure. Tl-6A1-'4M0 --1,875 F. furnace cool +1,550 F. 54,000

water quench +1,000 F. 8 hrs. (141-141-0-0) Widmanstatten` structure. 1 Ti-+0Al'-4'M0 1,550 F'. Water quench +900 F. 16 43, 700

hrs. (-164-17-38-6) Equiaxed alphrnbeta structure.

Referring to the table, the first heat treatment applied to each alloy consisted in heating above the 4beta transus to destroy the equiaxed structure, followed by a furnace cooled to below the `beta transus, and by a subsequent water quench from a temperature high in the alpha-beta field and thereupon aging at a ylower temperature in the alpha-beta field, the furnace cooling serving to impart the Widmanstatten structure of good hot creep strength, and the subsequent quenching and aging treatments serving -to strengthen the beta phase and impart higher room temperature strength and higher short time hot strength, without completely destroying the basic Widmanstatten structure. The second heat treatment applied to each alloy consisted in a water quench from a temperature high in the alpha-beta temperature field, followed by an aging treatment at a lower temperature thereby retaining the fine grained equiaxed alpha-beta structure and imparting optimum room temperature strength to the mater-ial. The beta .transus for these alloys is about 1775 to 1900 F. The room temperature tensile properties resulting from each heat treatment are given in parentheses in the order of ultimate strength-0.2% oiset yield strength-percent tensile elongation-percent area reduction, while the vbend creep properties are given at the right of the table as noted.

It will be seen from these data that the creep strength of each alloy heat treated to impart the Widmanstatten structure. is significantly higher than that orf thesame alloy heat treated to the non-Widmanstatten structure. In this case an attempt was made to obtain equal room temperature tensile strengths in both types of structures in` order that the inlluence of the Widmanstatten structure on hot creep strength might be made4 more clear. As regardsl room temperature tensile properties, it will be seen` that the alloys heat treated to have the non-Widmanstatten structure have much higher tensile elongations and area reductions than when heat treated to have the Widmanstatten structure.. Thus although the alloys when heat.` treated tov have the Widmanstatten structure have` the highest hot creep strength, they are inferior-in al1 assesses other respects, particularly, :as regards room temperature tensile properties, to the alloys processed in the alphabeta temperature field in acrdance with my said applications. Any desired compromise performance as between maximum hot creep strength and maximum roomy temperature tensile properties can of course be achieved in accordance with the teachings of the present invention by subjecting the alloy as heat treated to impart the Widmanstatten structure, to subsequent heat treatments as above noted in the alpha-beta temperature field as by quenching and subsequent aging to the extent and to the degree desired to secure the desired compromise properties.

If the processing of any of these alloys, as by forging or rolling, is completed while the temperature is still above the beta, transus, and the alloy thereafter slowly cooled to room temperature, the so-called unworked Widmanstatten structure will result. If, however, some limited working is continued as the temperature drops below the beta transus temperature, a so-called worked Widmanstatten structure will result. Figs. 1-3, inclusive, of the annexed drawings are illustrative of these effects. These figures show, respectively, `a macro and two microstructures of a Widmanstatten structure for a billet of the Ti-6A1-4V alloy as rolled above the beta transus. Since the center of the billet remained above the beta transus until the rolling was complete, it shows the unworked structure as in Fig. 2. During the rolling, however, the outside of the billet cooled below the beta transus before processing was complete, so it has a worked Widmanstatten structure as illustrated in Fig. 3. Continued working below the beta transus will break up this structure and produce the typical equiaxed alpha-beta structure in accordance with the processing of my applications aforesaid, macro and microstructures of which are shown in the annexed Figs. 4-6, inclusive., for comparison. In

these figures, as in Figs. 1 3, inclusive, a billet made of a Ti--6Al-4V alloy was worked in this instance, below `the beta transus in the alpha-beta temperature field, Fig. 4

lshowing a macrostructure and Figs. 5 and 6 showing microstructures as taken from the center of the billet, Fig. 5, and as taken from the edge of the billet, Fig. 6. Figs. 5 and.6 show clearly the fine grained equiaXed alphabeta microstructure or globular intermixture of these two phases resulting from plastic deformation in the alphabeta temperature field in accordance with my applications above mentioned. V

It should be emphasized that theV structures shown in Figs. 1-3, inclusive, versus those shown in Figs. 4-6, inclusive, were selected to illustrate the major differences `between the two types of structures, namely, the Widmanstatten, on the one hand, versus the fine grained equiaxed structure on the other. It should be borne in mind, however, that these alloys may be processed to provide a relatively smooth transition from :one type of structure to the other, so that at an intermediate stage both types of structures can be produced in a single specimen of these alloys. That is to say, the Widmanstatten structure produced by slow cooling from above the beta transus can be progressively broken up by subsequent working in the alpha-beta temperature field to provide smaller and smaller particles of the Widmanstatten structure as it is progressively broken up and converted to the equiaxed alpha-beta structure of Figs. 4-6, inclusive. Figs. 7-10, inclusive, of the accompanying drawings show the difference in 100 hour creep performance at four temperatures between 600 and 1000 F. for the Ti-7Al-4Mo alpha-beta alloy, as processed to provide the Widmanstatten structure on the one hand, versus processing in the alpha-beta temperature field to provide the non-Widmanstatten structure on the other hand. In each of these figures, the upper graphs A show the creep performance with the Widmanstatten structure, while the lower graphs B give the corresponding performance for the non-Wdman'statten structure. In each instance the Widmanstatten structure was obtained by forging the alloy above the beta transus of 1825 F., followed by annealing for 1 hour below the beta transus at 1450 F., slow cooling thence to 1050 F. and air cooling to room temperature, followed by aging for 24 hours at 1050 F. and air cooling. For the non-Widmanstatten structure of graphs B, to provide the equiaxed alpha-beta structure, the alloy was rolled below the beta transus, and thereupon aged for 6 hours at 1470 F. and air cooled, and thereupon aged again for 39 hours at 1020 F. and air cooled. Thus, the chemistries and the annealing schedules for the alloys thus processed to provide the Widmanstatten structure, on the one hand, and the non-Widmanstatten structure, on the other, were quite similar. Their structures, however, are completely different, as a result of the working temperature employed.

It will be seen fnom Figs. 7-,10, inclusive, that in each instance the alloy as processed to provide the Widmanstatten structure, has a much higher creep strength than the same alloy processed to have the non-Widmanstatten structure, irrespective of the temperature between 600 and 1000 F., employed for the creep tests. It is to be noted, however, that the superiority in. hot creep performance for the Widmanstatten structure versus the non- Widmanstatten structure is highest at the highest temperature 1000 F. employed, this difference becoming progressively less as the creep testing temperature was Vreduced to 600 F.

Abeta transus, andA (c) at 1650 F., below the beta transus.

"TABLE II Creep, structure and tensile properties of Ti-6Al-4V alloy after various processing schedules [Heat (l2-287662 (6.7Al-4.0V-0.13602) after forging at temperatures shown followed by 2 hour 1300 F. anneal] Forging Temperature 1,850 F. 1,750J F. 1,650 F. Microstrueture, Widman- Equi- Equistatten axed axed Creep 1n 50 hours at 50,000 p.s.1., 700 I".

percent.. 06 114 22 Room Temperature Tensiles:

Ultimate, p.S.i.X1,000 141 145 148 .2% Yield, p.S.l.X1,000 124 136 140 Elongation, percent-.-" 12 16 l5 RA., percent 35 44 48 The relative creep performance of the 'Ii-6Al-4V alloy is the same as for the Ti-7Al-4Mo alloy above discussed, namely, it is best for the Widmanstatten structure, and poorest for the alloy as forged at the lowest temperature of 1650 F. in the alpha-beta field. Microstructures of the l850 F. and 1650 F. forged specimens are shown in Figs. ll and l2, respectively, of the accompanying drawings. The Widmanstatten structure is clearly shown in the Fig. 9 microstructure based on the alloy specimen as forged above the beta transus; while the fine grained equiaxed microstructure resulting from forging in the alpha-beta temperature field is clearly shown in Fig. 10.

Reverting to Table II, it will be seen that the room temperature tensile properties of the alloys as thus forged are in the reverse order from their creep strengths, that is, best for the 1650 F. forging, still good for the 175 0 F. forging and poorest for the Widmanstatten structure developed by forging at 0 F. In this particular case, the differences in these respects shown in Table Il are not as great as I have ordinarily encountered inV similar comparisons. l-

Many tests which I have made have confirmed thatthe tensile properties of Widmanstatten structures are poorer than those 0f the equiaxed structures from the same heat.

Ingeneral, both 'strength and ductilities are lower for the `Widmanstatten structures, although reductions "in area happen to be the most sensitive to the Widmanstatten structures. Typical comparisions for the Ti-6Al-4V alloy are shown in Table II above discussed and in Table III presented below; and similar comparisons are shown 4for 'the `Ti'-7Al-4Mo alloy in the succeeding Table 1V.

TABLE =III Summary of heat treated properties obtained on material from fur'Ti-6Al-4V alloy heats processed to give structures shown [All samples heat treated 1 hour at 1700 F., WQ, age 4 holns at 1000* F.]

Heat Structure Ultimate 0.2% Percent Percent Yield El. R.A.

Equlaxed 160 149 13 44 -..do 160 147 13 46 Widmanstatten. 159 146 7 17 do 160 146 8 17 TABLE 1V Heat R 0910 (6.7A1-4.0M0, 1825 F. beta transus):

Widmanstatten structure developed by forging Just above beta transus. Anneal 1 hour 1450 F., slow cool to 1050 F., A C., 24 hours at 1050 F., A C. Equiaxed structure developed by rolling below beta transus. Same anneal as above. Heat Ril-203662 (6.8A1-4.0Mo, 1825 F. beta transus) Rolled below beta transus. Annealed 6 hours at 1470 F., A.C., 39 hours at 1020 F., A.C.

Widman- Equiaxed Equiaxed l OK at 170,000 p.s.i. 2 OK at 210,000 p.s.l.

All the above tables show that these alloys when processed to have the best creep properties, have the poorest room temperature tensile properties, the creep properties ttor the Ti-7Al--4Mo alloy of Table IV being given in Figs. 7-10, inclusive, above discussed.

What is claimed is: Y

1. The method of improving the elevated temperature creep strength of a titanium base alloy `containing about -2 to 15 atomic percent of at least one beta promoter sclected from the group consisting of molybdenum, vanadium, columbium, tantalum, chromium, manganese and iron, and up to 23% of .at least one alpha promoter selected from the group consisting of tin, antimony and aluminum, but not to exceed about 18% antimony and 10% aluminum, which comprises: heating said |alloy in the temperature range extending from substantially the beta transus and above until a substantially all-beta structure is obtained, and cooling thence to at least 50 F. belowthe beta transus at a rate such as to imparta Widmanstatten structure, and thereupon equilibrating the alloy at temperature in the range extending from labout ll00 F. up to about 50 F. below the beta transus and cooling substantially to room temperature.

2. The method of improving the elevated temperature creep strength of a titanium base alloy containing about 2 to l5 `atomic percent of at least one beta promote-r se lected from the group consisting of molybdenum, vanadium, columbium, tantalum, chromium, manganese and iron, and 0 to `23% of at least one alpha promoter selected :from .the --group consisting of tin, antimonp and aluminum, but not to exceed 18% antimony and 10% aluminum, which comprises: heating said alloy in the temperature range extending from substantially the beta transus and above until a substantially all-beta structure is obtained, and cooling thence to at least 50 F. below the beta transus at a rate such as to vimpart a Widmanstatten structure thereto, equilibrating the alloy at a tem perature in the range extending from about l F. kup to about 50 F. below the beta transus, and thereafter aging at about 750 to ll00 F.

3. The method of improving the elevated temperature creep strength and room temperature properties of a titanium base alloy containing about 2 to l5 atomic percent of at least 4one beta promoter selected from the group consisting of molybdenum, vanadium, columbium, tantalum, chromium, manganese and iron, up to 23% of at least one alpha promoter selected from the group consisting of tin, antimony and aluminum, but not to exceed 18% antimony and 10% aluminum, which comprises: heating said alloy in the temperature range extending from substantially the beta transus and above until ya substantially all-beta structure is obtained, and cooling thence to at least 50 F. below the beta transus at a rate such as to impart a VWidmanstatten structure, thereupon equilibrating the alloy in the temperature range extending from about 1100" F. up to about 50 F. below the beta transus, rapidly cooling thence to at least atmospheric temperature, and thereafter aging at about 7 50 to 1100 F.

4. The method of heat treating a titanium base alloy having at room temperature a mixed alpha-beta microstructure, for improving elevated temperature creep strength, which comprises: heating said alloy at temperature in the range extending from substantially the beta transus and above until a substantially all-beta structure lis obtained, thereupon cooling to at least 50 F. below the beta transus at a rate of about 3 to 30 F. per minute and such as to impart a Widmanstatten structure, thereupon equilibrating said alloy at temperature in the range extending from about 1l00 F. to 50 F. below the beta transus, and cooling thence to room temperature.

5. The method of heat treating a titanium base alloy having at room temperature a mixed alpha-beta microstructure, for improving elevated temperature creep strength and room temperature strength, which comprises: heating said alloy at temperature in the range extending from substantially the beta transus and above until a substantially all-beta structure is obtained, and cooling thence to at least 50 F. below the beta transus at a rate of about 3 to 30 F. per minute, and such as to impart a Widmanstatten structure, equilibrating said alloy within the temperature range extending from about 1l00 F. 'up toabout 50 F. below the beta transus and Cooling, and thereupon aging at elevated temperature below about 1l00 F.

6. A wrought and heat treated titanium-base alloy containing about: 2 to 15 atomic `percent of at least one beta promoter selected from the group consisting of molybdenum, vanadium, columbium, tantalum, chromium, manganese and iron, up to about 5% by weight of other beta promoters, up to about 23% by weight of alpha promoters selected from theV group consisting of tin, Vantirnony and aluminum, but not to exceed about 18%v 'antimony 'and 10% aluminum, balance substantially titanium, characterized in having'an equilibrated Widmanstatten microstructure and good-hot creep strength, and in having a room temperature tensile elongation of 'at least 2%.

7. A wrought and heat treated titanium-base alloy consisting essentially of about: 2 to l5 atomic percent of at least one beta promoter selected from the group consisting of molybdenum, vanadium, columbium, tantalum, chromium, manganese and iron, 1 to 23% by weight of at least one alpha promoter selected from the group consisting'oftin, antimony and aluminum, but not to exceed about 18% antimony and 10% aluminum, up to 5% by weight of other beta promoters, up to 0.3% carbon, up to 0.2% oxygen, and up to 0.1% nitrogen, each by weight, balance substantially titanium, characterized by an equilibrated Widmanstatten microsructure and by good hot creep strength at temperatures up to about 1000 F., and in having a minimum room temperature tensile elongation of about 2%.

8. A Wrought and heat treated titanium-base alloy consisting essentially of about: 2 to 15 atomic percent of vanadium, about 0.5 to 10% by weight of aluminum, carbon, oxygen and nitrogen by Weight up to about 0.3%, 0.2% and 0.1%, respectively, balance substantially titanium, characterized by an equilibrated Widman statten microstructure and good elevated temperature creep strength up to about 1000 F., and having a minimum room temperature tensile elongation of about 2%.

9. A wrought and heat treated titanium-base alloy consisting essentially of about: 2 to 15 atomic percent of molybdenum, about 0.5 to 10% by weight of aluminum, carbon, oxygen and nitrogen by weight up to about 0.3%, 0.2% and 0.1%, respectively, balance substantially titanium, characterized by an equilibrated Widmanstatten microstructure and good elevated temperature creep strength up to about l000 F., and in having a minimum room temperature tensile elongation of about 2%.

10. A wrought and heat treated titanium-base alloy consisting essentially of about: 2 to 15 atomic percent of molybdenum and vanadium, including at least one-half percent by Weight of each, 0.5 to 10% by weight of aluminum, carbon, oxygen and nitrogen by Weight up to about 0.3%, 0.2% and 0.1%, respectively, balance substantially titanium, characterized by an equilibrated Widmanstatten microstructure and by good elevated temperature creep strength up to about 1000 F., and in having a minimum room temperature tensile elongation of about 2%.

11. A wrought and heat treated titanium base alloy consisting essentially of about: 2 to 15 atomic percent of at least one beta promoter selected from the group consisting of molybdenum, vanadium, columbium,

tantalum, chromium, manganese and iron, 1 to 23% by Weight of at least one alpha promoter selected from the group consisting of tin, antimony and aluminum, but not to exceed 18% antimony and 10% aluminum, up to 5% by weight of other beta promoters, up to 0.3% carbon, up to 0.2% oxygen, up to 0.1% nitrogen, each by weight, balance substantially titanium, characterized in having an equilibrated Widmanstatten microstructure, a plastic creep at 800 F. of not more than about 0.1% when subjected to a stress of 50,000 p.s.i. for 100 hours, and in having a minimum room temperature tensile elongation of about 2%.

12. A Wrought and heat treated article for use under stress at elevated temperatures, made of a titanium base alloy consisting essentially of about: 2 to 15 atomic percent of at least one beta promoter selected from the group consisting of molydenum, vanadium, columbium, tantalum, chromium, manganese and iron, up to about 5% by weight of other beta promoters, 1 to 23% by Weight of at least one alpha promoter selected from the group consisting of tin, antimony and aluminum, but not to exceed 18% antimony and 10% aluminum, up to 0.2% in total amount of carbon, oxygen and nitrogen, balance substantially titanium, characterized in having an equilibrated Widmanstatten microstructure, a plastic creep at 800 F. of not more than about 01.1% when subjected to a stress or" 50,000 p.s.i. for 100 hours, and in having a room temperature tensile elongation of at least 2% and a minimum tensile strength of about 140,000

p.s.i.

References Cited in the tile of this patent UNITED STATES PATENTS 2,754,204 Jaffee July 10, 1956 OTHER REFERENCES ASM Preprint No. 7, 1953, isothermal Transformation of Titanium-Manganese Alloys, by Frost et al., pages 1-16, page 8 relied upon.

ASM Preprint No. 4, 1953, Heat Treatment of High Strength Titanium-Base Alloys, by Parri-s et al., pages 1-19, page 8 relied upon.

UNITED STATES PATENT oEETCE CERTIFICATION OF CORRECTION Patent N o. 2,968,586 January I7, 1961 Milton B. VOIdahl Column 3, line 54, for "macro" 4, TABLE I, first column thereof, undelf` the heading "Alloy", second line, for "Ti-6OMo-2AI" read Ti-Mo-QAI Signed land sealed this 6th day of June 196,17.

(SEAL) Attest:

ERNEST W. SWTDEE DAVID L. LADD Attesting Officer Commissioner of Patents

Claims

7. A WROUGH AND HEAT TREATED TITANIUM-BASE ALLOY CONSISTING ESSENTIALLY OF ABOUT: 2 TO 15 ATOMIC PERCENT OF AT LEAST ONE BETA PROMOTER SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM, VANADIUM, COLUMBIUM, TANTALUM, CHROMIUM, MANGANESE AND IRON, 1 TO 23% BY WEIGHT OF AT LEAST ONE ALPHA PROMOTER SELECTED FROM THE GROUP CONSISTING OF TIN, ANTIMONY AND ALUMINUM, BUT NOT TO EXCEED ABOUT 18% ANTIMONY AND 10% ALUMINUM, UP TO 5% BY WEIGHT OF OTHER BETA PROMOTERS, UP TO 0.3% CARBON, UP TO 0.2% OXYGEN, AND UP TO 0.1% NITROGEN, EACH BY WEIGHT, BALANCE SUBSTNTIALLY TITANIUM, CHARACTERIZED BY AN EQUILIBRATED WIDMANSTATTEN MICROSTRUCTURE AND BY GOOD HOT CREEP STRENGTH AT TEMPERATURES UP TO ABOUT 1000*F., AND IN HAVING A MINIMUM ROOM TEMPERATURE TENSILE ELONGATION OF ABOUT 2%.