钛合金激光立体成形中凝固与固态相变全流程微观组织演化机制

钛合金激光立体成形(Laser Solid Forming, 简称LSF)是增材制造技术的典型代表。当前两相钛合金LSF构件的延伸率及低周疲劳性能偏低，且存在明显的性能各相异性。这些力学性能的不足与其在凝固及固态相变过程中形成的微观组织密切相关。然而多周期循环往复、剧烈变温的工艺特点决定了LSF构件微观组织表现出强烈的非平衡性及复杂多变性，当前对其从凝固到固态相变的全流程形成机理仍认识有限，无法为LSF构件组织性能的优化调控提供有效指导。本项目采用耦合宏观有限元计算的相场法模拟技术，并结合关键性实验，研究钛合金LSF过程中从快速凝固到固态相变的全流程微观组织演化规律，分析特征组织的形成机理，探索工艺参数与宏观温度、应力分布以及微观组织之间的关联。项目的完成对于钛合金LSF构件微观组织主动调控及综合力学性能提升具有指导作用。

Laser solid forming (LSF) is a typical additive manufacturing technology. The titanium part made by LSF is suffered from low ductility and poor low cycle fatigue performance, as well as obvious anisotropic mechanical behaviors. All of these undesirable mechanical properties are related with the microstructure formed during both solidification and solid-state phase transformation. The multiple rapid thermal cycles result in the very complex non-equilibrium microstructure of LSF component. The present understanding of the microstructure evolution during the solidification and solid-state phase transformation is still very limited, which is insufficient to provide an effective guide for the improvement of property of LSF component. Using the micro-scale phase-field simulation method coupled with macro-scale finite element method, as well as combining with typical validation experiments, we intend to study the microstructure evolution in the whole process from solidification to the subsequent solid-state transformation, analyze the formation mechanism of various microstructure, and explore the relationship between manufacturing parameters, macro scale temperature distribution, stress distribution and microstructures. This work can provide a useful guide for the microstructure control and the improvement of mechanical properties.