The effect of strain rate and temperature on the tensile properties of NiAl

Abstract

Tensile testing of cast and extruded binary NiAl was performed from 300 to 900 K at strain rates of 1.4 × 10−4 to 1.4 × 10−1 × s−1. The brittle-to-ductile transition temperature (BDTT) was dependent on strain rate, with a three order of magnitude increase in strain rate resulting in approximately a 200 K increase in transition temperature. Regardless of strain rate, at temperatures just above the BDTT the fracture strength increased significantly and the fracture morphology changed from mostly intergranular to predominantly transgranular. It was also determined that the mechanism responsible for the brittle-to-ductile transition in NiAl had an apparent activation energy of approximately 118 kJ/mol. These results support the argument that the mechanism for the brittle-to-ductile transition in NiAl is associated with the onset of a thermally activated deformation process. This process is probably dislocation climb controlled by short circuit diffusion.