A determination of vacancy properties in AuNi solid solutions, via analysis of stress-induced and short range ordering kinetics

Abstract

Vacancy properties were studied in an α-Au-30 at.% Ni solid solution, with use of electrical resistivity and mechanical after-effect measurements, for the monitoring of short-range and stress-induced ordering kinetics, respectively. Both thermodynamical equilibrium concentrations and quenched-in supersaturations were considered for the vacancy defects. It is shown that, due to the inherent sensitivity of the methods used, valuable information about the vacancy parameters and related atomic mobility can be inferred from analysis of the ordering rate at low temperatures, that is in conditions of non-equilibrium for the α-phase. The respective activation energies for self-diffusion and vacancy migration which were derived from the rate temperature dependence are 1.85 and 1.10 eV, respectively. These values yield a consistent fit to the ordering pattern observed during quench and isochronal anneal cycles. Information about vacancy sink densities and life-times was inferred also. The salient feature of the results is that, while the atom jump rate is not substantially modified by alloying, vacancy mobility is markedly slowed down; conversely the vacancy formation energy appears to be strongly decreased. A Au-5 at.% Ni alloy for which the α-phase is stable at all temperatures was studied also.