Analysis of Enhanced Diffusivity in Nickel

The coefficient of self-diffusion in annealed and prestrained nickel single crystals, Du, determined in the temperature range 948° to 1023°K by radioactive counting of the surface is Du=1.9 exp(−66 800/RT) cm2sec−1. The coefficient of self-diffusion in annealed and prestrained fine-grained nickel crystals, Du′, in the same temperature range is independent of the degree of prestrain: Du′=1.1×10−7 exp(−32 300/RT) cm2sec−1. The coefficient of self-diffusion in nickel single crystals undergoing plastic deformation, Dd, was determined for strain rates ranging from 0.01 to 0.1035 h−1 in the same temperature range. Dd appears to vary with strain but eventually reaches an asymtotic value D̄d. At a constant temperature, D̄d/Du is almost linearly dependent on the strain rate ε: D̄d/Du=1+Kε̇, where K is 162, 225, and 470, (h−1) for temperatures 1023°, 973°, and 948°K, respectively.