Microstructure and high-temperature mechanical behavior of the NiAl-27 AT.% Cr intermetallic composite

A NiAl-27 at.% Cr composite material was prepared by a powder metallurgical route, involving argon atomization and consolidation by hot isostatic pres sing at 1350 degrees C for 4 h at 400 MPa. The consolidated material exhibi ted a fine-grained microstructure consisting of a fine dispersion of Cr par ticles of about 1.7 mu m in a NiAl matrix. The mechanical behavior at tempe ratures ranging from 650 to 1100 degrees C was investigated by tensile-stra in-rate-change tests. Analysis of the strain-stress data with both power la w creep and Garofalo's hyperbolic sine relation shows the transition to a l ow stress exponent creep regime with decreasing stress and/or increasing te sting temperature. The measured activation energy for deformation of 300 kJ /mol is consistent with the activation energy for Ni self-diffusion in Ni-5 0Al. Experiments with coarse grain sizes established that the creep rate is independent of grain size which suggests that the deformation mechanisms m ust be associated with the motion of lattice dislocations. (C) 1999 Acta Me tallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.