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 pressing at 1350 degrees C for 4 h at 400 MPa. The consolidated material exhibited a fine-grained microstructure consisting of a fine dispersion of Cr particles of about 1.7 mu m in a NiAl matrix. The mechanical behavior at temperatures ranging from 650 to 1100 degrees C was investigated by tensile-strain-rate-change tests. Analysis of the strain-stress data with both power law creep and Garofalo's hyperbolic sine relation shows the transition to a low stress exponent creep regime with decreasing stress and/or increasing testing temperature. The measured activation energy for deformation of 300 kJ/mol is consistent with the activation energy for Ni self-diffusion in Ni-50Al. Experiments with coarse grain sizes established that the creep rate is independent of grain size which suggests that the deformation mechanisms must be associated with the motion of lattice dislocations. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.