薄壁复杂结构钛合金异形件电子束增材制造成形机制研究

Thin-walled (wall thickness less than 5mm) complex shape titanium alloy structure function integration material in the modern aerospace, shipbuilding industry and other key areas have important application prospects. Poor precision parts, mechanical properties and other defects become the bottleneck restricting its application. In this project, electron beam powder bed additive manufacturing technology is adopted. Through the micro finite element structure analysis the heat, momentum transfer relaxation during special solidification process and the molten pool morphology, temperature and residual stress evolution mechanism. The boundary conditions and the orientation of solid martensitic transformation were proved, and the microstructure and mechanical properties of the component in a specific area were achieved. Combined with electron beam powder bed additive manufacturing technology with high preheating temperature, high vacuum pollution, self-tempering, etc.The project focus on the heat flow dynamics and heat stress evolution of the molten pool during the forming process and the grain orientation during the solidification process. The high temperature residual initial β-phase decomposition mechanism and temperature field (transient pool characteristics) interaction mechanism are mainly studied. By controlling of shape and performance, the research clarifies the relationship between micro-unit, phase transition, microstructure and mechanical properties. A homogeneous, thin-walled, complex titanium alloy shaped part structure and functionally integrated material with uniform microstructure and mechanical properties was prepared. The research results of this project have important reference value and research significance for the development of additive manufacturing technology and the application of thin-walled and complex titanium alloy parts.

薄壁（壁厚小于5mm）复杂形状钛合金结构功能一体化材料在现代航空航天、船舶工业等关键领域中有重要的应用前景，零件精度差、力学性能分散等缺陷成为制约其应用瓶颈。本项目采用电子束粉床增材制造技术，通过微单元有限元结构分析特殊凝固过程中热量、动量传递松弛与熔池形貌、温度及残余应力演化机理，探明固态相变马氏体分解边界条件、位向关系，实现构件在特定区域微观组织及力学性能；结合电子束粉床增材制造技术具有高预热温度、高真空无污染、自回火等优点，重点研究成形过程中熔池热流动力学及热应力演化行为、凝固过程中晶粒取向及高温残留初始β相分解机制与温度场（瞬态熔池特征）相互作用机制。通过控形和控性，阐明微单元-相变-显微组织-力学性能之间的关系，制备微观组织均匀细小和力学性能的均一的薄壁复杂钛合金异形零部件结构功能一体化材料。本项目的研究结果对增材制造技术发展及薄壁复杂钛合金零件应用有着重要的参考价值和研究意义。

具有薄壁（壁厚小于5mm）复杂形状钛合金结构功能一体化材料在现代航空航天、生物医疗、船舶工业等关键领域中有重要的应用前景。针对钛合金零件外部形状不规则、薄壁、具有双斜面结构、外形薄壁易变形，零件报废率高，加工周期长等制造难题。本项目首先将复杂薄壁构件将分解为不同厚度和不同成形角度的组合，研究增材制造成形不同厚度和角度的成形能力。研究发现随着壁厚的增加，薄壁构件的尺寸精度和表观密度逐渐增加。薄壁构件的相组成为αʹ相、少量α相和微量β相，主要发生的固态相变为：β→αʹ，在重熔区域，部分亚稳相αʹ相发生原位分解，从αʹ中析出成分不均匀的β，导致αʹ所含的V元素贫化，转变为α。针状αʹ马氏体的晶粒尺寸呈现出明显的层级结构。倾斜角度（30°和45°）样品中发现了块状相变，且块状相的晶粒尺寸随着构筑角度的变化而不同，30°样品中块状相晶粒尺寸约为5 μm，45°样品中块状相晶粒尺寸约为10 μm。其次，根据薄壁构件的基础研究，开展复杂点阵钛合金的力学性能研究。研究发现点阵材料的压缩/拉伸强度与压缩/拉伸弹性模量均随着长径比的减小而增加在点阵结构四周添加Z轴实体支柱加强筋，其沿Z轴的压缩强度较原始结构增加了295.81%，而密度仅增加了79.21%。最后，根据增材制造成形钛合金复杂构件存在塑性低（压缩应变普遍<10%）和高表面粗糙度的问题，研究了双重固溶+时效热处理以及预化学抛光微弧氧化双重表面改性处理对点阵结构的相成分、显微组织、力学性能的影响。双重固溶+时效热处理在均匀化显微组织、消除残余应力的同时获得了跨尺度的α板条与β纳米颗粒。预化学抛光微弧氧化双重表面改性技术在去除材料沉积态试样表面粘附粉末的同时亦保证了其承载能力。本项目的研究结果对增材制造技术发展及薄壁复杂钛合金零件应用有着重要的参考价值和研究意义。