Diffusion in single-phase samples was investigated, using a vapor/solid diffusion couple, at temperatures ranging from 1072 to 1572K. The Al was diffused by using a chemical transportation technique, with AlCl3 as the carrier, and NiAl with a high Al content was formed on the surface of a NiAl substrate of low Al content. The results showed that the interdiffusion coefficients at temperatures above 1367K were almost the same as previously published data. However, the interdiffusion coefficients within the composition range around the NiAl stoichiometry, at temperatures of between 1072 and 1324K, were extremely small. In particular, at temperatures of below 1123K, the compositional dependence of the diffusion coefficients exhibited a completely different tendency to that at higher temperatures. The composition range became wider as the temperature decreased. It was suggested that a miscibility gap existed within a certain composition range.

Single-Phase Interdiffusion in Intermetallic Compound NiAl M.Kato, H.Sasano, K.Honma, T.Suzuki: Journal of the Japan Institute of Metals, 1998, 62[8], 761-5