Stress decrease above the stress peak temperature (750K) was studied in <123> single crystals of Ni3(Al,3at%Hf). Two thermally activated deformation mechanisms were evidenced on the basis of stress relaxation and strain rate change experiments. From 500 to 1070K, the continuity of the activation volume/temperature curves revealed a single mechanism of activation enthalpy 3.8eV/atom and volume 90b3 at 810K with an athermal stress of 330MPa. Over the very same temperature interval, impurity or solute diffusion towards dislocation cores was evidenced through serrated yielding, peculiar shapes of stress-strain curves while changing the rate of straining and stress relaxation experiments This complicated the identification of the deformation mechanism, which was likely connected with cube glide. From 1070 to 1270 K, the high-temperature mechanism has an activation enthalpy and volume of 4.8eV/atom and 20b3, respectively, at 1250K.

Loss of Strength in Ni3Al at Elevated Temperatures. B.Viguier, T.Kruml, J.L.Martin: Philosophical Magazine, 2006, 86[25-26], 4009-21