Study on Morphological Stability of Interphase Boundary Formed by Diffusional Reaction

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The control of morphology of the interface between different phases is one of the key technology in producting composite materials. In the present work, the phase interfaces in Ti-X, Fe-C base and Ni-Al base systems have been studied from the viewpoints of both the experimental and thermodynamics.(1)alpha/beta interface in Ti-X system : In rge alpha/beta diffusion couples of Ti-X alloys, non planar interfaces were formed for Fe, Co and Ni. This result might due to high speed diffusion of these elements in alpha solid solution.(2)alpha/gamma interface in Fe-C-X system : The alpha/gamma interfaces formed by carburization in Fe-C-X (X : Ti, V, Nb, Ta, Cr, Mo, W, Co and Cr) alloys were stable, while non planar interfaces were observed for P, Al, Sb, Ni, Mn, Si and Ge. These results could be explained quantitatively by the concept of the local equilibrium.(3)Pseudo-interface in beta phase of Ni-Al base diffusion couples : In a single phase region of beta phase in the Ni-Al base couples, an interface which has a clear concentration drop was observed in the concentration profile. This is due to the anomalous variations in diffusion coeffecients in B2 structure arising from its composition dependent defect structure.