深过冷Ni_(80.3)B_(19.7)合金的再辉和非规则共晶的形成

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

采用熔融玻璃净化结合气体保护的方法,使Ni80.3B19.7过共晶合金获得了407K的大过冷度,研究了其在不同过冷度下快速凝固过程中的再辉行为.结果表明,Ni80.3B19.7过共晶合金在0-112K过冷度范围内无明显再辉,在112-323K过冷度范围内,其再辉曲线表现为两个再辉峰,而在323-407K过冷度范围内,其再辉曲线为一个再辉峰.初生固相含量的随着过冷度的增大而增大,导致一次再辉度随着过冷度的增大而增大.深过冷Ni80.3B197合金凝固组织中非规则共晶的形成,归因于共晶两相在快速凝固阶段以自由枝晶的形式进行的非耦合生长和再辉后的慢速凝固阶段两相枝晶所发生的形态上的转变.

Ni80.3B19.7 hypereutectic alloy melt was undercooled to 407 14（0.295 TL） 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 323～407K, 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.