EFFECTS OF ENVIRONMENT AND HEAT-TREATMENT ON THE TENSILE AND FATIGUE PROPERTIES OF TI-24 AT-PERCENT-AL-11 AT-PERCENT-NB

The alpha(2) + beta alloy Ti-24 at%Al-11 at%Nb was evaluated for mecha nical properties in the as-received, mill annealed condition (nearly e quiaxed) and in the beta annealed condition (basketweave). The as-rece ived condition had a moderately strong basal transverse alpha(2) textu re which gave a higher yield strength, higher elastic modulus, and hig her fatigue crack growth rate (FCGR) for loading in the transverse dir ection at room temperature. The beta annealed material was stronger an d more isotropic in both texture and properties. The fatigue crack gro wth rate is higher at 732 degrees C in argon than at room temperature. A hydrogen environment results in a FCGR at 732 degrees C comparable to or less than the FCGR in argon at 732 degrees C for the as-received and beta annealed conditions respectively. Although the hydrogen in s olution at levels as high as several thousand ppm does not embrittle a t elevated temperature, embrittlement is found after cooling to room t emperature.