Within the framework of density functional theory, an investigation was made of 3 key properties of a C interstitial solid solution in crystalline Ni. These were the heat of solution, ΔH, the activation energy for C diffusion, E, and the C-C pair binding energy, B. In addition, the effect of Ni magnetism upon each property was assessed. The most energetically favorable lattice site for C was the interstitial octahedral site (O-site), which was 1.59eV lower in energy than the tetrahedral site (T-site). Using the nudged elastic band method, it was determined that diffusion between O sites proceeded via a T-site intermediate. The calculated activation energy (E = 1.62eV) was in good agreement with published experimental data (1.54 to 1.71eV). The binding of C pairs was sensitive to magnetization effects, and was negligible (B ≈ 0eV) in the ferromagnetic state, but repulsive in the paramagnetic state (B = –0.2eV). These results were consistent with anelastic relaxation experiments, which gave B < 0.1eV for the ferromagnetic state. The calculated heat of solution in the paramagnetic Ni state (ΔHp = 0.2 to 0.35eV) was in reasonable agreement with high-temperature experimental values of about 0.4eV, and the magnitude of ΔH in the ferromagnetic state was found to be about 0.4eV greater than that in the paramagnetic state.

First-Principles Study of the Solubility, Diffusion and Clustering of C in Ni. D.J.Siegel, J.C.Hamilton: Physical Review B, 2003, 68[9], 094105 (7pp)