深过冷技术制备均质过偏晶合金及其形成机制的研究

Preparation of Homogeneous Hypermonotectic Alloy by High Undercooling Technique and Research on Formation Mechanism

采用熔融玻璃净化和循环过热相结合的方法使Ni 40 % (质量分数 )Pb合金获得 2 92K大过冷度 ,成功制备出大体积均质过偏晶合金。根据BCT模型和组织演化结果分析表明 :过冷粒状晶是在内应力的作用下 ,枝晶发生全面碎断 ,随后在枝晶段表面和应变能的驱动下使晶界移动发生再结晶的结果 ,即枝晶碎断 再结晶机制 ;试样基体上弥散分布的细密铅颗粒是由于快速凝固阶段溶质截留效应而形成的 ,少量较大尺寸铅颗粒的形成主要与慢速凝固阶段分布于枝晶骨架间残余富铅液相的聚合有关。

With the complex method of molten glass purification and superheating cycling, bulk homogeneous Ni 40wt% Pb hypermonotectic alloy were prepared successfully under the undercooling of 292K. The granulation mechanism of granular grains was analyzed based on the microstructural observation as well as the calculations of the solid/liquid phase transition velocity, the dendrite growth velocity and undercooling with BCT model of dendrite growth. It was concluded that the undercooled granulation consisted of two stages. The dendrite is, firstly, broken into fragments owing to the stress caused by uneven shrinking during rapid solidification, then under the driving force of surface and strain energies, the fragments merge through the migration of boundaries. i.e.,recrystallization. The refined lead particles resulted from the lead separation out from the supersaturated primary dendrites formed during rapid solidification because of solute trapping, and the relative large lead particles were mainly due to the aggregation of residual Pb rich melts during common soldification.