Masahiko Kato1, Hisaoki Sasano2,Kazuhiro Honma2 and Toshiyuki Suzuki1
1Department of Mechanical Engineering, Graduate School of Engineering, Kogakuin University, Tokyo 163-8677
Interdiffusion in single-phase NiAl was investigated using a vapor-solid 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 substrate of low aluminum composition. The results obtained showed that interdiffusion coefficients at the temperatures above 1367 K are almost the same as already reported. However, it was found that the interdiffusion coefficients in the composition range around the stoichiometric NiAl at the temperatures between 1072 and 1324 K are extraordinarily small. Particularly, below 1123 K at which little is known, the composition dependence of the diffusion coefficients showed a completely different 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 composition range of NiAl phase is discussed.
(Received March 24, 1998; In Final Form June 10, 1998)
intermetallic compound, interdiffusion, nickel aluminide, vapor-solid diffusion couple, miscibility gap, phase separation
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