BDT and Creep Behaviors of NiAl-25 at. pct Cr Alloy at Various Temperatures

Brittle-to-ductile transition (BDT) behavior and creep behavior of extruded NiAl-25Cr alloy at elevated temperatures were investigated. The results reveal that the alloy exhibits obvious BDT behavior with the increase in temperature and BDT temperature (BDTT) is sensitive to initial strain rate. When the initial strain rate increases by two orders of magnitude, BDTT has an increase of approximate 80 K. The creep data in the temperature range of 1073～1123 K reveal two distinct regions of creep behavior in this material. At lower temperature, the creep characteristics are consistent with structural controlled creep process where creep deformation is controlled by dislocation climb. At higher temperature, the creep characteristics are consistent with mobility-controlled deformation where viscous glide of dislocations controls creep. The apparent activation energy determined by creep in both regions exceeds the value for lattice self-diffusion in NiAl by a considerable amount. This can be explained in terms of the simultaneous deformation of second phase particles (γ'-Ni3Al and α-Cr phase) along NiAl matrix during creep.