氢处理-轧压复合对增材制造钛合金显微组织的调控机理研究

The metallurgical structure of metal parts made by Laser Additive Manufacturing material is easy to form columnar crystal and coarse primary grain, which restricts its application on the bearing component. In this project, the idea of combining hydrogenation-rolling-dehydrogenation in laser melting deposition is proposed for titanium alloy, and the comprehensive properties of the component can be improved by the metallurgical regulation of the structure. The mechanism of hydrogen on the thermal-dynamic mechanism of element diffusion, grain nucleation and growth will be revealed by studying on the melting mechanism and metallurgical process of hydrogenated titanium powder. Investigating the influence of hydride formation and decomposition on nucleation, the experimental relationship between hydrogen content and nucleation density, grain intrinsic state (grain size D0, lamellar thickness d) will be constructed. The behavior and law of hydrogen induced high temperature plastic deformation of the deposition alloy in the unsteady state temperature field will be investigated, and the experiment of combining hydrogenation- rolling and laser melting deposition will be carried out. The mechanism of non spontaneous nucleation under the influence of multiple factors would be revealed. The thermal and dynamic conditions of the critical columnar to equiaxed transition (CET) would be determined, and based on this the transformation of CET process will be optimized and established. Finally obtaining the correlation between hydrogen content, rolling pressure, microstructure process and mechanical properties. The research results can provide theoretical basis and experimental basis for precise control of grain size and metallurgical microstructure in Laser Melting Deposition, and promote development of metallurgical theory of incremental manufacturing.

激光增材制造的金属零部件冶金组织易形成柱状晶及粗大初生晶粒，制约了其在承力构件上的应用。本项目提出钛合金置氢-轧压-除氢复合激光熔化沉积的思路，通过组织结构的冶金调控，进而实现构件综合性能提升。研究置氢钛合金粉末熔化机制及冶金过程，揭示氢对元素扩散、晶粒形核长大的热-动力学作用机理；研究氢化物形成与分解对形核质点的影响，阐明氢含量与形核密度、晶粒本征状态（晶粒大小D0，片层厚度d）间的对应关系；研究非稳态温度场内沉积态合金的氢致高温塑性变形行为及规律，开展置氢-轧压复合激光熔化沉积实验；研究复合工艺参数对组织形成、演变的影响及其控制机理，揭示多因素影响下非自发形核的机制，确定临界柱状晶/等轴晶转变(CET)的热-动力学条件，优化并建立CET转变工艺；最终获得氢含量-轧压量-组织-工艺-力学性能相关性；研究成果可为激光熔化沉积冶金组织精准控制提供理论基础和实验依据，促进增材制造冶金理论发展。

增材制造超常冶金环境及其循环沉积制造的显著特征导致成型后钛合金冶金组织柱状晶显著，项目基于氢在钛合金中的可逆合金化原理及其塑形变形细化晶粒的理论，提出了氢处理轧压复合实现组织细晶化的新方法新途径。通过气相充氢和氢化钛混合充氢的方式，系统研究了置氢对钛合金激光沉积成形过程熔池内冶金行为的影响，建立氢对单道沉积、搭接、循环沉积宏微观形貌的影响；通过系统微观组织分析揭示了氢对熔池内溶质元素扩散和凝固形核、晶粒长大的热力学动力学作用以及亚稳相转变机理。掌握了加热冷却过程氢化物生成与分解及其对形核质点的影响，构建了氢含量与晶粒本征状态、相组成间的实验关系，揭示了钛合金非平衡凝固过程氢对溶质扩散、凝固形核及亚稳相变机理的冶金调控机制，从凝固热力学动力学角度阐明了氢对熔池内冶金机制的影响。开展了置氢-变形复合增材工艺研究，通过打印、热塑性变形揭示了氢致沉积态组织热塑性变形机理，建立了含氢沉积态组织循环热处理的再结晶和柱状晶/等轴晶转变的临界条件；建立了置氢-变形对激光熔化沉积熔池内非自发形核质点影响机制，确立了柱状晶/等轴晶转变的关键因素，发展了适用于增材制造组织等轴化，细晶化的方法。项目成果未来有望为钛合金组织调控及拓展应用于航空航天领域钛合金关键承力结构中。