Abstract
For the purpose of studying interdiffusion in the ζ-solid solution of a Ni–Al system, the experiments were performed using a method of vapor-solid couple at 1273∼1573 K . As a vapor source, the fine chips of 12 mass% Al–Ni alloy (ζ+ε phases) were used. The surface concentration of Al in the diffusion annealed test pieces almost coincided with the solubility limit reported in the phase diagram of the Ni–Al system at each experimental temperature.
Fine alumina markers placed on the surface of test pieces prior to diffusion were found in its inside after annealing at each temperature. The composition at the marker position indicated a higher Al concentration with an increase in annealing temperature. The ratio of the intrinsic diffusion coefficients of these two constituents, DAl⁄DNi, was 1.3∼7.0 at the marker position.
The interdiffusion coefficients (\ ildeD) were dependent upon the annealing temperature and Al concentration, and were evaluated to be the orders of 10−15∼10−13 m2/s in this experimental temperature range. Log \ ildeD increased almost linearly with increasing Al concentration.
The activation energies for interdiffusion (\ ildeQ) obtained from the temperature dependence of \ ildeD decreased from 282 to 258 kJ/mol with increasing Al concentration. The impurity diffusion coefficeint of Al in Ni, DAl, at each temperature was obtained from extrapolating of \ ildeD to 0 at%Al and its activation energy, QAl*, obtained from the Arrhenius plot of DAl* was evaluated to be 284 kJ/mol.
The relationship between the entropy term, \ ildeD0, and \ ildeQ can be represented by the following equation:
ln(\ ildeD_0/m^2·s^-1)=3.1×10^-5(\ ildeQ/J·mol^-1)-16.0.
