| Diffusivity [D], and square-root diffusivity [r] matrices for the ternary Ni-Cr-Mo alloy in the approximate single-phase compositional range of Hastelloy C-22 (Alloy 22) were determined for 1215 C. These data will contribute to the understanding of the long-term phase stability of Alloy 22, and its potential use as a corrosion barrier in nuclear waste packages. Experimental diffusion couple data were obtained at selected temperatures from a series of diffusion couples, and evaluated using the constant-diffusivity approach. The approach here treats the data analysis as an optimization problem that simultaneously considers concentration profile data from numerous diffusion couples surrounding a single end-point composition. We make use of the mathematical characteristics of the analytical solution to this problem, reducing the number of parameters to be fitted. The parameter fitting is accomplished using a combination of heuristic and deterministic methods. Discussion of the sources of uncertainty in the diffusivity values is included. |
