SINGLE-PHASE INTERDIFFUSION IN INTERMETALLIC COMPOUND NIAL

Interdiffusion in single-phase NiAl was investigated using a vapor-sol id diffusion couple in the temperature range between 1072 and 1572 K. Aluminum was diffused by a chemical transportation technique in which aluminum chloride was used as the carrier gas and consequently NiAl of high aluminum composition was formed on the surface of the NiAl subst rate of low aluminum composition. The results obtained showed that int erdiffusion coefficients at the temperatures above 1367 K are almost t he same as already reported. However, it was found that the interdiffu sion coefficients in the composition range around the stoichiometric N iAl at the temperatures between 1072 and 1324 K are extraordinarily sm all. Particularly, below 1123 K at which little is known, the composit ion dependence of the diffusion coefficients showed a completely diffe rent tendency from that at higher temperatures. The composition range became wider as the temperature decreased. Based on these experimental results, the possibility that a miscibility gap exists in a certain c omposition range of NiAl phase is discussed.