Enhanced superplasticity of ultra-fine grained Ti-17 powder compact prepared through HIP/IF

The superplasticity of ultra-fine grained Ti-17 powder compact prepared through hot isostatic pressing and isothermal forging was investigated in the range of temperature from 780 °C to 920 °C and strain rate from 5 × 10−4 to 1 × 10−2 s−1. A uniform microstructure with the size of many equiaxed α phases less than 1 μm was produced. Superplastic tensile experiments indicate that this ultra-fine grained Ti-17 powder compact exhibits superplasticity in all tested conditions and a maximum elongation-to-failure of 1353% is obtained at temperature of 830 °C and initial strain rate of 5 × 10−4 s−1. During superplastic deformation of prepared Ti-17 powder compact, the coarsening of the microstructure is seriously influenced by the coalescence of dynamically recrystallized grains and the superplastic failure is caused by a combination of necking, cavity growth and cavity interlinkage. Almost all prepared Ti-17 powder compact specimens present better superplasticity than conventional cast and forged Ti-17 alloy even at high strain rate of 10−3 s−1.