Rate controlling creep mechanisms in Ti alloys were studied at 1000°F (811°K) as as a function of stress, alloy composition, and heat treatment. Alloying additions of Si, Bi, Ge, Fe, Mo and Nb were added to a base alloy composition of Ti-5Zr-5Al and their effect on creep behavior established. The results of this model alloy study showed dislocation creep was the rate controlling creep mechanism in all alloys, with precipitation on mobile dislocations becoming important in limiting dislocation mobility in the alloys containing Si. In addition, the model alloy study resulted in the selection of two alloys that showed good creep resistance for further creep and mechanical properties evaluations. These were Ti-5Al-5Zr-0.5Si and Ti-5Al-5Zr-lMo-0.5Si. Together with the two model alloys two Si bearing commercial alloys, Ti-11 and IMI-685, were also studied. The creep rate controlling mechanism for the commercial alloys was also shown to be precipitation on mobile dislocations. Both the commercial alloys and the two optimum model alloys resulted in similar creep properties with the Ti-5Al-5Zr-lMo-0.5Si alloy having the greatest creep resistance.
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