Brittle-to-ductile transition of a multiphase intermetallic alloy based onNiAl

The microstructure and mechanical behaviors of a multiphase beta + gamma gamma' + alpha-Cr Ni-Al-Cr alloy have been investigated. This alloy exhibit s only 1% tensile ductility despite the presence of the continuous ductile phases. It is noted that both fractograph and BDTT are typically dependent on strain rate, with a two orders of magnitude increase in strain rate resu lting in approximately a 150 K increase in BDTT. An asymmetry between the c ompressive and tensile yield strength was also observed at low temperature. SEM observation of the side surface of the fractured specimen indicated th at the phase boundary seemed to be weaker than the fracture strength of the constituent phases at temperature below the BDTT; the random orientation r elationship between the beta phase and the gamma/gamma' phases may result i n difficulty in strain transfer from soft phase to hard phase, which, in tu rn, contributes to crack initiation at phase boundary. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.