过偏晶合金Ni-40%Pb深过冷凝固组织

采用熔融玻璃净化与循环过热相结合的方法研究过冷Ni-40%Pb(质量分数)过偏晶合金的组织演化规律. 结果发现 过偏晶合金在快速凝固阶段本质上是以枝晶方式生长; 当ΔT《50K时, 合金组织为粗大枝晶+枝晶间Pb相+团块状Pb相; 当100《ΔT《198K时, 合金组织宏观偏析严重; 当ΔT＝292K时, 合金组织呈粒状晶, 第二相均匀弥散分布. 分析表明凝固组织宏观偏析与快速凝固阶段固液相变速率和体系残余液相分数有关; 粒状晶粒化机制属于枝晶碎断再结晶机制.

Solidification structures in deep-undercooled Ni-40%Pb hypermonotectic alloys

Structural evolution in undercooled Ni 40%Pb(mass fraction) hypermonotectic alloys was investigated systematically by employing the method of molten glass purification combined with superheating cycling. Within the achieved undercooling range of 0 to 292?K, the structures were classified into three categories. When the undercooling was less than 50?K, coarse dendrites and interdendritic lead lumps comprised the major characteristics of hypermonotectic alloys. With increasing the undercoolings into the range of 100?K to 198?K, the macrosegregation was serious. When the undercooling was up to 292?K, the granular grains formed, and the refined lead particles distributed homogeneously in the whole sample. Analytical result shows that the degree of macrosegregation is related to the solid/liquid phase transition velocity and the residual liquid fraction during the rapid solidification stage. The granulation mechanism of undercooled granular grains is owing to the dendrite breaking up and recrystallization.