激光增材制造技术在航天构件整体化轻量化制造中的应用现状与展望

采用激光增材制造技术制备了组织致密且无缺陷的Ti6Al4V/NiTi仿生功能梯度材料 (bionic function graded materials, BFGM)，并对其界面微观结构、析出相特征和力学性能进行了研究. 结果表明，Ti6Al4V/NiTi BFGM呈现由多种晶粒形貌和不规则异常共晶组织组成的非均匀组织，主要为富钛和富镍的固溶体以及(Ti, Ni)化合物. 随着 NiTi合金含量增加，不同沉积层中析出相的数量和形态发生了显著变化. BFGM的显微结构发生了一系列转变：α + β双相组织→柱状晶 + 不规则共晶结构→柱状晶→等轴晶→等轴晶 + 柱状晶. 凝固过程中的相聚集、分离和偏析现象严重影响BFGM的力学性能，BFGM最大显微硬度为730.9 HV，归因于脆性Ti₂Ni相的存在. BFGM的抗拉强度为202 MPa，断后伸长率为6.5%，显著高于直接连接的Ti6Al4V/NiTi异种材料. 拉伸断口具有脆性断裂特征，多个次级裂纹沿晶扩展.

Research status of laser additive manufacturing in integrity and lightweight

Ti6Al4V/NiTi bionic function graded materials (BFGM) with dense and defect-free microstucture were prepared by laser additive manufacturing technology, and their interfacial microstructure, precipitation phase characteristics and mechanical properties were investigated. The results show that the Ti6Al4V/NiTi BFGM exhibits a non-uniform microstructure consisting of various grain morphologies and irregular and abnormal eutectic tissues, which are mainly titanium-rich and nickel-rich solid solutions and (Ti, Ni) compounds. As the content of NiTi alloy increases, the number and morphology of precipitated phases in different deposition layers change significantly. The microstructure of BFGM undergoes a series of transformations: α + β biphasic microstructure → columnar crystals + irregular eutectic structure → columnar crystals → equiaxial crystals → equiaxial crystals + columnar crystals. Phase aggregation, separation and segregation during solidification have significantly affected the mechanical properties of BFGM. The maximum microhardness of BFGM is 730.9 HV, which is attributed to the presence of brittle Ti₂Ni phase. The tensile strength is 202 MPa and the elongation is 6.5%, which is significantly higher than that of the directly connected Ti6Al4V/NiTi heterogeneous material. The tensile fracture is characterized by brittle fracture with multiple secondary cracks extending along the crystal.