Bulk diffusion coefficients were measured, at homologous temperatures of up to 0.94T, by using a 63Ni tracer (table 9). No curvature was observed in the Arrhenius plot. Differential scanning calorimetry was performed on the same samples, after quenching from 820 or 1015C. This revealed 2 annealing stages; in agreement with previous positron annihilation data. At low temperatures, the activation energy (1.1eV) of a stage which was centered at about 180C was attributed to Ni mono-vacancy migration. It was assumed that a second stage, centered at about 380C, corresponded to the break-up of vacancy clusters. Its activation energy (2.6eV) was in agreement with that (2.42eV) for the bulk diffusion of Ni.

A.Jennane, E.H.Sayouty, J.Bernardini, G.Moya: Philosophical Magazine Letters, 1997, 76[1], 33-40

Table 9

Diffusivity of 63Ni in Ni2Si