Superplastic Properties of Fine Grain TIMETAL® 54M (Ti-5Al-4V-0.75Mo-0.5Fe)

Ti-5Al-4V-0. 75Mo-0. 5Fe alloy (Ti-54M, US Patent No. 6,786,985) is a new alloy developed at TIMET. The alloy exhibits superior machinability in most machining conditions and strength comparable to that of Ti-6Al-4V. The flow stress of the alloy is typically 20%similar to 40% lower than that of mill-annealed Ti-6Al-4V under similar test conditions, which is believed to be one of contributors to its superior machinability. Superplastic forming (SPF) properties of this alloy were investigated and a total elongation exceeding 500% was observed at temperatures between 750 degrees C and 850 degrees C at a strain rate of 10(-3)/S. A steady flow behavior that indicates the occurrence of superplasticity was observed at temperature as low as 790 degrees C at a strain rate of 5 X 10(-4)/S. It is well understood that grain size is one of critical factors that influences superplasticity. Fine grain Ti-54M sheets with 2-3 mu m of grain size, produced in a laboratory facility, demonstrated that SPF would be possible at temperatures as low as 700 degrees C. This paper will present superplastic behavior of fine grain Ti-54M compared with Ti-6Al-4V and discuss metallurgical factors that control low temperature superplasticity.