Rapid crystal growth in undercooled hypoeutectic Cu-Sb alloys

High undercoolings of up to 141K(0.176T_L) were achieved for a bulk hypoeutectic Cu_37.5Sb_62.5 alloy using the glass fluxing method. The solidified microstructures were then investigated for the purpose of understanding rapid crystal growth from undercooled melts of a binary eutectic system containing one intermetallic compound. It was found that the microstructures of this alloy depend strongly on the undercooling level prior to solidification. At small undercoolings, coarse plates of the primary intermetallic Cu₂Sb compound coexist with rod-like eutectic structure. Moreover, the larger the undercooling level, the finer both the primary phase and the eutectic structure. As the undercooling level is increased to above 84K, however, the primary phase is changed from faceted Cu₂Sb plates to Sb dendrites, and the eutectic structure changes from the above regular eutectic structure to an anomalous one. In order to understand such changes in the microstructure, the growth velocities of two primary phases and the eutectic growth velocity versus the undercooling level were calculated in terms of the current theories on rapid crystal growth from undercooled melts.