Analysis of Enhanced Diffusivity in Nickel

Abstract

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.

On the strain‐enhanced diffusion of α‐iron

“…From the fact mentioned above, we can conclude that the observed strainenhanced diffusion of alpha iron is explained on the basis of the diffusioncontrolled glide motion of screw dislocations having jogs. It is hoped to confirm whether or not the same interpretation can be applied to the strain-enhanced diffusion of other materials [5] On the other hand, large differences were observed between NX1 and N1* in the paramagnetic temperature region. They are much larger than those expected from the grain growth during creep deformation.5) This implies that j ) During creep deformation in the paramagnetic temperature region, the grain growth was observed by optical microscopy; 1 , grew larger by 40%.…”

A study of nucleation and the early stage of growth of nickel powder from a vapour nickel carbonyl precursor

“…For re-crystallisation of the interior of these particles, volume diffusion would be required. Wazzan has developed an expression for the volume self-diffusion coefficient of nickel (Wazzan and Dorn, 1965). Eq.…”

In situ nuclear magnetic resonance study of defect dynamics during deformation of materials

“…It is well known that plastic deformation results in an increased number of vacancies which are produced from climbing jogs on dislocations [9,12,[14][15][16][17][18][19][20]. While theoretical analyses [14][15][16] clearly point to the strain-enhanced diffusion due to the excess vacancies produced during plastic deformation, experimental studies (tracer diffusion, creep, etc.)…”

“…While theoretical analyses [14][15][16] clearly point to the strain-enhanced diffusion due to the excess vacancies produced during plastic deformation, experimental studies (tracer diffusion, creep, etc.) failed to yield consistent results [17][18][19][20], and Ruoff and Balluffi [14][15][16] cited experimental data on creep which exhibited no such presence of excess vacancies. The present NMR study as well as the previous one by In both equations, the coefficients al and ~2 are functions of the plastic strain.…”