Taiji Nishizawa1 and Akira Chiba1
1Department of Materials Science, Faculty of Engineering, Tohoku University, Sendai
Eifert et al have recently reported that the aluminum contents in the α/β interface in Cu-Al diffusion couples are higher than those given by the equilibrium phase diagram. Similar experiments on the α/γ interface in γ Fe-Cr diffusion couples in this work have proved that the chromium contents in the interface are considerably lower than those in α and γ phases of the equilibrated two-phase alloys. These experiences suggest that the condition of interphase equilibrium is affected by the rate of atom transfer across the phase interface. A phenomenological consideration has been given to the rate of atom transfer concerning the chemical potential gradient and the atomic mobility in the interface layer. The mobility of the α/γ interface in the γ Fe-Cr system has been estimated to be about 1/500 of that of lattice diffusion in the α phase. This concept has also been applied to analyze a result on the non-equilibrium α/α interface found in α Fe-Cr diffusion couples heated at a temperature between 830° to 910°C for a long time, and the reason why the equilibrium phase γ is missing has been discussed.
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