Flow behavior and mechanisms of NiAl–9Mo alloy during superplastic deformation

The superplastic deformation of the as-extruded NiAl–9Mo eutectic alloy is observed as a function of temperature and strain rate, and characterized by the constitutive equation and the deformation microstructure. In the region of high strain rate (and low temperature), the flow curve exhibits a stress peak followed by weak softening, and then by a dynamic restoration (DR) process. The activation energy of deformation in this region is estimated to be Q=207 kJ/mol, similar to that of bulk diffusion in NiAl. It is suggested that the mechanism associated with DR is responsible for the deformation in this region. In the region of low strain rate (and high temperature) the flow curve exhibits continuous work hardening until fracture, and concomitant grain boundary sliding and grain growth occur. The activation energy of deformation in this region is estimated to be Q=113 kJ/mol suggestive of grain boundary diffusion in NiAl. Larger tensile elongation, i.e., superplastic deformation, is observed in the latter region.