SUPERPLASTICITY IN TIAL AND TI3AL 2-PHASE MATERIAL MADE FROM PREPED POWDER

Ti-47 mol%Al alloy powder produced by plasma rotating electrode proces s (PREP) was consolidated by HIPing at 1 423 K and 176 MPa for 10.8 ks . Isothermal hot forging (IHF) with the small samples cut from the as- HIPed compact at 1 223 K and an initial strain rate of 3.8 x 10(-4) s- 1 up to 78% reduction in height was carried out. This IHF process was considered to proceed by super plastic flow. A large pancake (approxim ately 25 mm thick with 140 mm diameter) without any crack was successf ully obtained from the as-HIPed large compact (approximately 60 mmphi with 100 mm height) by the similar 78% IHF process. The results of the tensile strain-rate-change test and elongation to failure test of the specimens machined from the pancake indicated that this material exhi bits fine grain superplasticity at elevated temperature higher than 1 223 K. The maximum elongation to failure value of 398% was obtained at 1 323 K and an initial strain rate of 2.8 x 10(-4) S-1.