三元Co-Cu-Pb偏晶合金的快速凝固组织形成规律研究

在自由落体条件下实现了三元Co-Cu-Pb合金的液相分离与快速凝固. 实验发现,随液滴直径减小,Co₅₁Cu₄₇Pb₂合金液滴发生由枝晶→两层壳核→枝晶组织的转变,Co₄₇Cu₄₄Pb₉合金液滴的组织形态由壳核组织演化为均匀组织. 两种合金的快速凝固组织均由α(Co),(Cu)和(Pb)固溶体三相组成,α(Co)和(Cu)相主要以枝晶方式生长,(Pb)相分布在(Cu)枝晶间. 关键词： 液相分离 偏晶合金 快速凝固 自由落体

Microstructure formation mechanism of rapidly solidified ternary Co-Cu-Pb monotectic alloys

The metastable phase separation and rapid solidification of ternary Co-Cu-Pb monotectic alloys have been investigated under free fall condition. With the decrease of droplet diameter, the microstructures of Co₅₁Cu₄₇Pb₂ and Co₄₇Cu₄₄Pb₉ alloys display a "dendrite→core-shell→dendrite" transformation and a morphology transition from core-shell to homogeneous microstructure, respectively. X-ray diffraction analysis indicates that the solidified microstructures are composed of α(Co), (Cu) and (Pb) phases. α(Co) and (Cu) phases grow mainly in dendritic manner, and (Pb) phase is distributed interdendritically among (Cu) phase. Both experimental results and theoretical calculations reveal that the interfacial energy between (Co)/(Pb) liquid phases is larger than thoses of (Co)/(Cu) and (Cu)/(Pb) phases. The weak wetting ability between (Co) and (Pb) liquids results in the distribution of (Pb) phase inside the Cu-rich zone instead of Co-rich zone. Three possible solidification routes are deduced according to the solidification microstructure, in which the solidification process consists of phase separation L→L₁(Cu)+L₂(Co), peritectic transformation α(Co)+L→(Cu) and monotectic transformation L(Cu)→S(Cu)+L(Pb).