Grain boundary precipitation reactions in a wrought Fe-8Al-5Ni-2C alloy prepared by the conventional ingot process

Abstract

Phase transformations in the Fe-8Al-5Ni-2C alloy, prepared by rapid solidification process (RSP), have been studied by Choo and Kim. They showed that the microstructure of the alloy in the as-solidified condition was austenite phase ({gamma}) containing fine ordered L{prime}1{sub 2}-type precipitates. The formation of these fine ordered L{prime}{sub 2}-type precipitates, lying along the directions in the matrix, was attributed to the spinodal decomposition. It was also shown that, on aging at 823 K, the fine ordered precipitates grew and, at the same, {alpha}(ferrite) and {kappa}-carbide formed by a heterogeneous reaction at the {gamma}/{gamma} grain boundaries. With increasing aging time, the heterogeneous reaction became predominant, leading to a two-phase microstructure of {alpha} and {kappa}-carbide in the end. Recently, the authors performed transmission electron microscopy (TEM) observations of the phase transformations in the Fe-8Al-5Ni-2C alloy, prepared by conventional casting process. It was found that the microstructure of the alloy in the as-quenched condition was austenite phase containing fine ordered L{prime}1{sub 2}-type precipitates, similar to the previous results for the as-solidified alloy. However, when the as-quenched alloy was aged at 823 K for a long time, the equilibrium microstructure was observed to be a mixture of ({alpha} + B2 + {kappa}-carbide), rathermore » than {alpha} + {kappa}-carbide as reported by Choo and Kim.« less