过冷Ni-31．44％Pb偏晶合金凝固行为

采用熔融玻璃净化和循环过热相结合的方法研究Ni-31.44%Pb偏晶合金宽过冷区间凝固组织演化规律;结果表明,过冷偏晶合金在快速凝固阶段首先形成枝晶α骨架,再辉重熔后分布于枝晶间的残余液相按照平衡凝固模式进行后续反应;在0～286K过冷范围内,当ΔΤ＜50K时,合金凝固组织为粗大枝晶α+枝晶间Pb相;当70＜ΔT＜232K时,凝固组织为细密枝晶α+枝晶臂上细小的Pb颗粒+枝晶间Pb相;当ΔT＞242K时,凝固组织为过冷粒状晶+均匀细小的Pb颗粒+少量尺寸较大的枝晶间Pb颗粒,过冷粒状晶的粒化机制属于枝晶碎断-再结晶机制.

Solidification Behavior of Undercooled Ni-31.44% Pb Monotectic Alloy

Solidification behavior of undercooled Ni 31.44%Pb monotectic alloy was studied systematically by employing the complex method of molten glass denucleating combined with thermal cycling. Results of structural evolution showed that undercooled monotectic alloy solidified in the form of dendrite essentially during the stage of rapid solidification and after recalescence, the residual melts between the dendrites solidified in the equilibrium mode. Within the achieved undercooling range, the solidification structures were classified into three categories. When the undercooling was less than 50K, the structures were composed of coarse dendrites and interdendritic lead phase. With the undercooling increasing into the range of 70 to 232K, the dendrites were refined and because of solute trapping, fine lead particles separated out from supersaturated dendrite arms. When the undercooling exceeded 242K, the granular structures formed. The granulation mechanism of undercooled granular grains is owing to the primary dendrite disintegration and recrystallization.