The kinetics of vacancy annihilation and short range order formation in Ni 11.4 at % Cr

Abstract

In Ni-Cr alloys annealing after quenching from high temperatures leads to an increase of electrical resistivity which is attributed to a short range order state often denoted as K-state. Here the kinetics of the formation of the K-state in a Ni 10% Cr alloy is investigated by resistivity measurements for different quenching and annealing temperatures. The measurements are analyzed by an extended Schulze-Lücke method [22] which assumes that the rate of resistivity change is proportional to the vacancy concentration and that this rate as well as the rate of vacancy annihilation is described by a chemical rate equation. This analysis allowed a quantitative determination of the parameters determining the kinetics of short range order formation under different vacancy concentrations as well as the kinetics of annealing out of the quenched-in surplus vacancies. Among other quantities this treatment yielded the activation energies for vacancy formation H F = 1.16 eV, for vacancy migration H M = 1.56 eV and, as an independent cross check, for self diffusion H D = 2.73 eV in good agreement with H F + H M = 2.72 eV.