Microstructure Selection in the Interdendritic Region During Directional Solidification of a Ni-23at.%Al Alloy

摘要

Directional solidification experiments of a binary Ni-23at.%Al alloy were carried out to examine the effects of growth velocity on the microstructure selection in the interdendritic region. Only the growth velocity was changed from 5 μm/s to 60 μm/s under a given thermal gradient. As a result, the noticeable change in the microstructure during solidification occurred between the y dendrites. The γ interdendritic microstructure was varied as a function of growth velocity from rod γ-γ' coupled peritectic structure to planar y' structure and then to eutectic structures consisting of stable γ'-p eutectic and metastable γ-p, eutectic structures. The microstructure selected preferentially among the y dendrites was considered by calculating the interface temperature of a phase growing into its parent melt. It is shown that the microstructure selection in the y interdendritic region is determined by a phase or a structure kinetically leading at the highest interface temperature under a given growth condition.