Superplasticity in NiAl intermetallics macroalloyed with iron

In this paper, we aim to examine the superplastic behavior of an extruded N i-28.5Al-20.4Fe (at.%) alloy, which consists of beta+gamma phases with an a verage linear intercept grain size of 30-50 mum. Its tensile properties wer e determined at temperatures from 1123 to 1323 K and initial strain rates f rom 1.04 x 10(-2) to 1.04 x 10(-4) s(-1). A maximum elongation of 233% was obtained at 1123 K and a strain rate of 5.2 x 10(-4) s(-1). Transmission el ectron microscope (TEM) observation found many dislocation-free grains adja cent to grains with a high-dislocation density and subgrains and subgrain b oundaries, which indicate that dynamic recrystallization has occurred as an efficient accommodation mechanism. Scanning electron microscope (SEM) exam ination of the fracture sample after superplastic deformation reveals many voids on the fracture surface. By correlating with the results of TEM obser vation, it is suggested that the superplastic deformation in this alloy sho uld be controlled by a grain boundary sliding-based mechanism accommodated by the movement of dislocation and dynamic recrystallization. (C) 2001 Else vier Science B.V. All rights reserved.