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 3 1.44%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～ 2 86K过冷范围内 ,当ΔΤ <5 0K时 ,合金凝固组织为粗大枝晶α +枝晶间Pb相 ;当 70 <ΔT <2 3 2K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 >2 42K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 4 0 %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 <5 0K时 ,合金组织为粗大枝晶 +枝晶间Pb相 +团块状Pb相 ;当 10 0 <ΔT <198K时 ,合金组织宏观偏析严重 ;当ΔT =2 92K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。

Microstructures and evolution mechanism of highly undercooled Ni-Pb hypermonotectic alloy

The microstructures and evolution mechanism of the undercooled Ni-20%Pb（molar fraction） alloy were investigated systematically by high undercooling solidification technique. The experiment results indicate that the morphology of α-Ni phase and the distribution of Pb element in undercooled Ni-20%Pb alloys change with the increase of undercooling. The main evolution mechanisms of α-Ni are dendrite remelting and recrystallization. Pb phase in the microstructure of Ni-20%Pb hypermonotectic alloy originates from L2 phase separated from the parent melt during the cooling process through immiscible gap and L′2 phase formed at the temperature of monotectic transformation. The solubility of Pb element in α-Ni phase under high undercooling condition is up to 5.83% which is obviously higher than that under equilibrium solidification condition. The real reason that causes the solubility difference is distinct solute trapping.