Anomalous eutectic formation in undercooled Ni-P eutectic alloy

To investigate the relationship between anomalous eutectic and the remelting of primary phase, thin samples of Ni-19.6at.%P eutectic alloy were solidified over a range of undercoolings with temperature recalescence depressed. Fully regular eutectic structures were obtained. The thin samples were then rapidly heated to certain temperatures between the nucleation and eutectic temperatures, resulting in anomalous eutectic structure. It was found that the volume fraction of anomalous eutectic increased with increasing target temperature. alpha-Ni particulates were in principle randomly oriented while beta-Ni3P phase was well oriented in the anomalous eutectic formed upon heating. Considering that alpha-Ni is a solid solution while beta-Ni3P is a stoichiometric intermetallic compound, it is unambiguous that anomalous eutectic forms due to remelting of the primary regular eutectic.