激光增材制造高性能钛合金结构件的微观组织调控及强韧化机理

The anisotropic characteristic of coarse columnar crystals in the microstructure of Laser Additively Manufactured (LAM) titanium alloys seriously weakens the integrated mechanical properties of the components. Especially, the fracture toughness and low-cycle fatigue behavior of LAM titanium alloy structural parts are far inferior to those of forged ones. Consequently, demands for LAM technology of high-performance titanium alloys from the national defense industries, such as aero-engines and aerospacecrafts industry, cannot be satisfied. To address this issue, the microstructure control methods and toughening mechanisms of LAM high-performance titanium alloy structural parts are detailed researched from the following aspects: (1) The grain size and distribution of LAM as-deposited titanium alloys are controlled and regulated with physical and chemical refining methods, respectively; (2) Formation mechanism of residual stresses in LAM titanium alloys is revealed firstly, then the hereditary property and evolution rules of the as-deposited microstructure during heat treatment are discussed, finally the recrystallization mechanism of as-deposited microstructure of LAM titanium alloys during heat treatment is clarified; (3) Mechanical behavior modelling of as-deposited microstructure under different load modes is constructed, then the degradation and strengthening mechanisms of grain boundaries and inner-grain substructures on the mechanical properties are explained, and next, the failure and fracture mechanisms of LAM titanium alloy parts under different load modes are studied, meanwhile, the toughening mechanisms of the microstructure of LAM titanium alloys are interpreted, and the integrated mechanical properties of the LAM titanium alloy components finally approach or briefly exceed the forging standards. The research is expected to lay a foundation for the LAM fabrication of high-performance titanium alloy structural parts which are applied in large aircrafts.

针对激光增材制造（LAM）钛合金中存在粗大柱状晶组织，该组织各向异性的特点又严重影响钛合金的综合力学性能，尤其使得钛合金结构件的断裂韧性和低周疲劳性能远不如锻件，无法满足国家航空飞机与发动机和航天飞行器等国防工业对高性能钛合金LAM技术的迫切需求。重点研究激光增材制造高性能钛合金结构件的组织控制及强韧化机理。采用物理与化学细化法调控LAM钛合金沉积态晶粒的大小和分布；理清LAM钛合金残余应力形成机制，揭示热处理时钛合金沉积态组织的遗传性及其演化规律，明晰沉积态组织经受热处理时的再结晶机制；建立沉积态组织在不同加载模式下的力学行为模型，揭示晶界结构、晶内亚结构对力学性能的劣化或强化机理，研究LAM钛合金不同加载模式下的失效与断裂机理；揭示钛合金LAM组织的强韧化机制，实现LAM钛合金综合力学性能达到或优于锻件水平，为大型飞机用高性能钛合金结构件的激光增材制造技术奠定科学技术基础。

针对激光增材制造（LAM）TC4钛合金中存在粗大柱状晶组织，其各向异性对结构件的力学性能产生不良影响，使得钛合金结构件的断裂韧性和低周疲劳性能远不如锻件。课题主要通过（1）变质处理；（2）超声冲击；（3）热处理三种方法辅助激光增材制造，获得静态力学性能优于锻件；动态力学性能优于或接近锻件。为航空航天（C919大飞机）制造关键承力结构件提供调控LAM TC4钛合金的组织性能并有效降低各向异性奠定理论与技术基础。.主要研究内容：（1）LAM TC4钛合金成形工艺及沉积态组织形成规律研究；（2）硼变质处理对LAM TC4钛合金组织性能与各向异性的影响；（3）硼变质处理对TC4钛合金动载力学性能（断裂韧性和低周疲劳性能）的影响；（4）搭建超声冲锻辅助激光增材制造实验平台并确定最佳的工艺参数；（5）超声冲锻对LAM TC4钛合金组织性能与各向异性的影响；（6）不同热处理工艺对LAM TC4钛合金组织性能与各向异性的影响；（7）不同热处理工艺对LAM TC4钛合金断裂韧性和低周疲劳性能的影响规律；（8）研究LAM TC4钛合金LAM的强韧化机制和疲劳失效机制；（9）深入剖析LAM TC4钛合金成形工艺-微观组织-力学性能之间的内在机理与对应关系。.重点研究了激光增材制造高性能钛合金结构件的宏微观组织调控技术及其强韧化机理；揭示了LAM TC4钛合金粗大柱状晶的形成机理；探讨了控制和细化钛合金晶粒的有效方法；制定了适合于钛合金LAM技术特征的热处理工艺与规范；最终实现了LAM TC4钛合金结构件水平与垂直两个方向的静态力学性能都超过锻件并且水平与垂直两个方向的各向异性都小于5%；动态力学性能的断裂韧性优于锻件且低周疲劳性能与锻件相当。LAM高性能钛合金结构件的研究为航空航天等装备制造产业的跨越式发展奠定了技术基础，以满足国家航空航天和国防工业对激光增材制造高性能钛合金技术的需求。