SUPERPLASTIC DEFORMATION AND MICROSTRUCTURE EVOLUTION IN PM IN-100 SUPERALLOY

The superplastic deformation behaviour of PM IN-100 alloys consolidated by hot isostatic pressing (HIP) was investigated in compression tests at temperatures between 1323 and 1373K. The microstructural changes were observed using scanning electron microscopy. In the high strain rate region, grain refinement occurs due to dynamic recrystallization, resulting in the work softening type stress-strain curves. At low strain rates, grain growth occurs during deformation corresponding to work hardening. The strain rate sensitivity index, m, reaches a maximum value (m = 0.6) at the optimum strain rate which depends on the test temperature. The grain size dependence coefficient, p, was determined to be 2.0. The activation energy for deformation was 348kJ mol-1. The rate-controlling mechanism of superplasticity in as HI Ped IN-100 seems to be the grain-boundary sliding controlled by volume diffusion rather than grain-boundary diffusion. © 1990 Chapman and Hall Ltd.