自由落体条件下三元Ni-Pb-Cu偏晶合金的快速凝固

来源期刊:中国有色金属学报2009年第2期

论文作者:罗炳池 王海鹏 魏炳波

文章页码:279 - 285

关键词:Ni-Pb-Cu偏晶合金;自由落体;快速凝固;壳核组织;表面偏析

Key words:Ni-Pb-Cu monotectic alloy; free fall; rapid solidification; core-shell microstructure; surface segregation

摘    要:在自由落体条件下研究三元Ni62Pb30Cu8偏晶合金的相分离与快速凝固。XRD分析结果表明;凝固组织由固溶体(Ni)和(Pb)两相构成;随液滴直径减小,三元Ni62Pb30Cu8偏晶合金从壳核组织演变为(Pb)相颗粒分布在 (Ni)枝晶间的组织;在形成的壳核组织中,表面张力较小的(Pb)相始终占据最外层,有利于降低表面相和体系总吉布斯自由能。能谱测定发现,在固溶体(Ni)和(Pb)相中,溶质截留效应十分显著。采用传热模型计算了不同直径液滴的冷却速率与过冷度,二者均随液滴直径的增大而减小。理论分析了合金液滴的内部温度梯度与第二相L(Pb)液滴的Maragoni迁移,发现第二相L(Pb)液滴充分实现二次相分离。在自由落体条件下,合金液滴的最终凝固组织由冷却速率、表面偏析、Marangoni迁移和(Ni)枝晶生长共同决定。

Abstract: The phase separation and rapid solidification of ternary Ni62Pb30Cu8 monotectic alloy were investigated under free fall conditions. X-ray diffraction analysis indicates that the solidified microstructure consists of (Ni) and (Pb) phases. With the decrease of droplet diameter, the morphology transforms from a triple-layer core-shell microstructure into (Ni) dendrite microstructure. In the triple-layer core-shell microstructure, the surface layer is (Pb) phase, which is favourable to reducing the surface Gibbs free energy. EDS analyses reveal that both (Ni) and (Pb) phases exhibit conspicuous solute trapping effect during rapid solidification. The calculated cooling rate and undercooling increase exponentially with the decrease of droplet diameter. Furthermore, the Maragnoni migration of the second liquid (Pb) phase was studied, which indicates that the L(Pb) phase droplets can migrate to the central part. Under free fall conditions, the cooling rate, surface segregation, Maragnoni migration and dendrite growth are responsible for the microstructure evolution.

基金信息:国家自然科学基金资助项目

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