Titanium alloys of the Ti.sub.3 Al type

Details Titanium alloys of the Ti.sub.3 Al type Titanium alloys of the Ti.sub.3 Al type

1979-07-25

1981-09-29

Rutledge, L. Dewayne

Specialized metallurgical processes, compositions for use therei

Processes

Free metal or alloy reductant contains magnesium

148 115F, 148 127B, 148 325, 148133, C22C 1400, C21D 100

Patent

active

042920779

ABSTRACT:
Titanium-aluminum-niobium alloys having narrow and critical composition ranges are disclosed. The alloys have room temperature tensile elongations of 1.5% or greater and creep strength to density ratios better than certain nickel superalloys. Thus, they may replace other heavier base alloys in many applications up to 750.degree. C. Aluminum content must be closely controlled as excess amount decreases ductility while insufficient amount decreases creep strength. Niobium content is also critical as excess amount adversely affects creep strength-to-density ratio while insufficient amount decreases ductility. And there is an important interrelationship between niobium and aluminum.
Disclosed are alloys having atomic percent compositions of 24-27 Al, 11-16 Nb, balance Ti; more preferred are alloys of 24.5-26 Al, 12-15 Nb, balance Ti. (Nominally, these alloys in weight percent are Ti-13/15Al-19.5/30Nb and Ti-13.5/15Al-25/28Nb.) Vanadium is uniquely found to be substitutional for niobium in the foregoing alloys in amounts up to 4 atomic percent, thereby reducing density and increasing strength-to-density ratio while maintaining properties. Mechanical properties are dependent on heat treatment. For the best combination of strength and ductility, the alloys are heated or forged above the beta transus and controllably cooled to produce a fine Widmanstatten microstructure.

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McAndrew et al., "Investigation of Ti-Al-Cb System . . . ", Wadd Tech. Rpt. 60-99, Apr. 1960, pp. iii, 15, 16.
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