Analysis of Enhanced Diffusivity in Nickel

Abstract

The coefficient of self‐diffusion in annealed and prestrained nickel single crystals, D_u, determined in the temperature range 948° to 1023°K by radioactive counting of the surface is $$D_u\text{=1.9\hspace{0.17em}}\exp \text{(−66\hspace{0.17em}800/RT)\hspace{0.17em}}{\mathrm{cm}}^2{\sec }^{\text{−1}}$$ . The coefficient of self‐diffusion in annealed and prestrained fine‐grained nickel crystals, $D_u^{\prime }$ , in the same temperature range is independent of the degree of prestrain: $$D_u^{\prime }{\text{=1.1×10}}^{\text{−7}}\hspace{0.17em}\exp \text{(−32\hspace{0.17em}300/RT)\hspace{0.17em}}{\mathrm{cm}}^2{\sec }^{\text{−1}}$$ . The coefficient of self‐diffusion in nickel single crystals undergoing plastic deformation, $D_d$ , was determined for strain rates ranging from 0.01 to 0.1035 h⁻¹ in the same temperature range. $D_d$ appears to vary with strain but eventually reaches an asymtotic value ${\mathrm{D̄}}_d$ . At a constant temperature, ${\mathrm{D̄}}_d{\mathrm{/D}}_u$ is almost linearly dependent on the strain rate ε: $${\mathrm{D̄}}_d{\mathrm{/D}}_u\text{=1+Kε̇}$$ , where K is 162, 225, and 470, (h⁻¹) for temperatures 1023°, 973°, and 948°K, respectively.