Pseudo-interface formation and diffusion behaviour in the B2 phase region of NiAl-base diffusion couples

The microstructure and concentration profiles in the B2 phase region of the diffusion couples of Ni-AI-X (X: Ti, V, Cr, Mn, Fe, Co and Cu) ternary systems were examined by EPMA. A pseudo-interface between beta(1) (low Al) / beta(2) (high Al) characterized by a sharp change in the concentration profiles of both Al and the alloying element is observed in composition range near 50at%Al. The characteristic features of the concentration profiles in the Ni-AL base ternary diffusion couples are presented and the up-hill diffusion of alloying elements observed at the pseudo-interface of the Ni-AI-X (X: Ti, V, Cr, Mn, Fe, Co and Cu) ternary systems is discussed from a thermodynamic point of view.