Recalescence behavior and formation of anomalous eutectic in the deeply undercooled Ni_(80.3)B_(19.7)alloys

Ni80.3B19.7 hypereutectic alloy melt was undercooled to 407 K(0.295TL) with fluxing glass and gas protection technique. The recalescence behaviors were investigated. When the initial undercooling is less than 112 K, recalescence is a slow temperature-cooling course. There are two recalescence peaks, when the alloy melts is undercooled between 112 K and 323 K, the first one is accord with the crystallization of primary phase Ni3B and the latter is caused by the eutectic solidification. While the undercooling lies in the range of 323-407 K, only one recalescence peak appears in the cooling curve. The recalescence rises up with the increasing of undercooling, because the volume of primary solid phase increases with the undercooling increasing. Based on the experiment results, thermodynamic and kinetic theory, the formation mechanism of anomalous eutectic was elucidated.