Microstructure of rapidly solidified Cu-25Â wt.% Cr alloys

Rapid solidification of Cu-25 wt.% Cr alloys was carried out by melt spinning at three wheel speeds 4, 12 and 36 m/s. The microstructure of the ribbons was investigated by scanning electron microscopy (SEM). It was found that the ribbons generally have a microstructure consisting of a fine dispersion of a Cr-rich phase in a Cu-rich matrix, and that the morphology and size of the Cr-rich phase vary with the wheel speed. For lower wheel speeds, the Cr-rich phase shows dual morphologies, dendrites and spheroids. The Cr-rich dendrites are all distributed around the Cr-rich spheroids, and have a larger amount on the free surface than on the wheel surface. The Cr-rich spheroids show a wide distribution of size, and have a larger mean size on the free surface than on the wheel surface. In the ribbons of the lowest wheel speed, small Cr-rich spheroids tend to gather around those big ones forming spheroid clusters. For the highest wheel speed, the Cr-rich phase shows one morphology, spheroids, and a reduced size. The results were discussed with respect to the formation of the Cr-rich spheroids during rapid solidification.