On the origin of the anelastic relaxation effect in Ni₃Al

Abstract

A mechanism is proposed for the anelastic relaxation effect observed at high temperatures for Ni₃Al by Gadaud and Chakib (1993, Mater. Sci. Forum, 119—121, 397). The dependence of the relaxation magnitude on the crystal orientation as found by Mourisco et al. (1996, J. Phys. Paris, IV, C8—235) strongly suggests that the effect is due to stress-induced redistribution of point defects on the sublattice sites for Ni atoms. Both the kinetic and the thermodynamic aspects of the relaxation can be explained quantitatively in terms of reorientation of antisite Al atoms. The properties of the point defects relevant to the effect have been calculated by a thermodynamic model of the Bragg-Williams type and by atomistic computer simulation. The rate and the magnitude of the relaxation observed in experiment are in reasonable agreement with theoretical values estimated from the results of these calculations.