超声场中三元复杂包晶型合金的悬浮无容器快速凝固研究

Ultrasonic levitation, which combines containerless processing, high undercooling and acoustic cavitation effects, is an effective method to investigate the solidification process of metallic materials under nonequilibrium conditions. In this proposal, the ultrasonic levitation, drop tube and phase field methods are applied to explore the rapid solidification mechanisms of highly undercooled ternary Ti/Cu based peritectic alloys. Special attention is paid to the shape oscillation and capillary wave of acoustically levitated alloy droplets. The relationship between the kinematics and thermophysical properties of levitated alloy droplet will be established. The specific heat and surface tension of undercooled alloys are determined through non-contact measurements. The undercoolability of liquid alloys and competitive nucleation of the primary and peritectic phases with different crystallographic features are systematically studied. Meanwhile, the mechanisms of coupled growth of these various phases will also be revealed. The influence of highly undercooled state on the solidification microstructures and physical properities is to be clarified. Based on the phase field theory, the formation of solidification microstructures will be analyzed dynamically. The relation between phase selection, crystal growth, microstructure and physical properties will be investigated in details. The final objective is to develop the peritectic solidification theory of multicomponent alloys and to design new peritectic-type materials with high performance.

超声悬浮技术有效集成了无容器、深过冷和空化效应等物理条件，为开展极端非平衡条件下金属材料凝固规律研究另辟路径。本项目选取三元Ti/Cu基包晶型合金作为研究对象，以超声悬浮实验方法为主，辅以自由落体微重力凝固技术，并借助相场理论模拟方法，系统研究三元复杂包晶型合金的深过冷和快速凝固过程。探索超声悬浮条件下合金液滴的形态振荡和表面波动规律，建立悬浮液滴运动特征与熔体热物理性质之间的函数关系，实验测定深过冷合金熔体的比热和表面张力。重点研究超声悬浮合金熔体的过冷行为以及初生相和包晶相的竞争形核规律，分析不同结晶形貌初生相和包晶相的协同生长机制，阐明非平衡凝固条件下三元包晶型合金微观组织和物理性能的相关规律。结合相场理论方法对微观组织形成过程进行动态分析，系统揭示复杂包晶型合金“相选择-组织形态-微观结构-物理性能”之间的本征关系，丰富包晶凝固理论，发展新型高性能多元包晶型金属结构材料。

本项目采用超声悬浮无容器处理方法，辅以落管微重力快速凝固技术，对三元Co-Cu-Sn和多元Ti-Al-X(X=Nb,V)包晶型合金的深过冷和快速凝固机理进行系统的实验研究。主要取得以下五个方面的研究成果：一是揭示了大体积悬浮物体与超声场的交互作用机理，发现了物体尺寸的增大显著增强了声波的阴影效应，阐明了二束相向传播声波的合成可以补偿悬浮驻波场。二是设计并建立了单轴式双束超声悬浮实验系统，成功实现了两类波长级饼状物体和直径半波长钢球的超声悬浮。三是实现了超声悬浮状态下包晶型合金熔体的深过冷和快速凝固，发现超声悬浮促进了离异共生组织和包晶相形核生长的新，熔体复杂运动和声流效应有利于获得均匀凝固组织。四是系统探索了三元包晶型合金快速凝固组织与力学性能之间的相关规律，系统揭示了三元Ti-Al-Nb合金在不同凝固条件下的相选择规律，阐明了快速凝固组织与显微硬度和力学性能的相关规律，进一步发现了低密度TiAlNbV中熵合金在高速应变条件下具有较好的抗剪切变形能力。五是建立了多元单相合金深过冷快速枝晶生长与强韧化机理的内在联系，实现了固溶强化和析出相强化等多种性能调控途径，这一研究成果为新型先进金属材料的高通量设计和成分优化提供重要依据。以上述五方面研究结果为主要内容，发表高水平论文11篇，刊登科普文章1篇，申请和授权国家发明专利5项，获陕西省科学技术二等奖1项和中国材料研究学会一等奖1项。培养博士研究生2人，硕士研究生4人。本项目的研究丰富和发展了超声悬浮原理和技术，同时为高性能金属材料的仿空间制备提供了关键的实验数据和预研基础。