激光熔化沉积TiAl合金的组织与力学性能

Microstructure and Mechanical Properties of TiAl Alloy Fabricated by Laser Melting Deposition

摘要:

利用激光增材技术能够制造形状复杂的TiAl合金零部件，从而进一步拓展这一轻质高温合金在航空航天领域的工程应用。但目前对激光熔化沉积TiAl合金工艺、组织及性能之间内在关系的研究较少。以Ti-48Al-2Cr-2Nb合金粉末为实验材料，采用激光熔化沉积技术制备了宏观质量良好的TiAl合金试样，系统研究了优化工艺参数条件下沉积层的显微组 织、相组成、硬度分布以及沉积试样的室温力学性能。结果表明，沉积层的显微组织结构主要由大量γ-TiAl相和少量的 α₂-Ti₃Al相构成；沉积层组织表现出由柱状晶、等轴晶、胞状晶及板条状组织形成的层带组织特征，沉积层组织内的晶粒细化较明显。沉积层的硬度分布范围为537~598 HV_0.3，底部的维氏硬度比中部及顶部高。TiAl合金试样在室温下的极限 抗压强度为(1545±64) MPa，压缩应变为(17.68±0.07)%；室温下沿激光扫描方向的极限抗拉强度为(514±92) MPa，断后伸长率为(0.2±0.04)%；沿构建方向的极限抗拉强度为(424±114) MPa，断后伸长率为(0.15±0.07)%，TiAl合金试样的室温拉 伸断口形貌特征属于准解理断裂。通过优化扫描策略并辅以后续热处理，有望改善合金组织均匀性及力学性能的各向 异性。

Abstract:

Complex shaped TiAl alloy components can be manufactured by laser additive manufacturing technology, further expanding the engineering applications of this lightweight high-temperature alloy in the aerospace field. However, there is currently limited research on the intrinsic relationship among the laser melting deposition process, microstructure, and properties of TiAl alloys. TiAl alloy specimens with good macroscopic quality were prepared by laser melting deposition using Ti-48Al-2Cr-2Nb alloy powder as raw materials. The microstructure, phase composition, hardness distribution of the deposited layer, and room temperature mechanical properties of the deposited specimens were studied under optimized process parameters. The results show that the microstructure of the deposited layer mainly consists of a large number of γ-TiAl phases and a small amount of α₂-Ti₃Al phases; the microstructure of the deposited sample exhibits a layer characteristics formed by columnar crystals, equiaxial crystals, cytosolic crystals, and laths structure, and the grain refinement in the microstructure of the deposited layer is obvious. The hardness distribution of the deposited layer ranges from 537 HV_0.3 to 598 HV_0.3, and the Vickers hardness at the bottom is higher than that at the middle and the top. The ultimate compressive strength of the TiAl alloy specimens is (1545±64) MPa at room temperature, with a compressive strain of (17.68±0.07)%, and the ultimate tensile strength along the scanning direction of the laser is (514±92) MPa at room temperature, with an elongation of (0.2±0.04)% after break; the ultimate tensile strength along the building direction is (424±114) MPa, with an elongation of (0.15±0.07)% after break. The tensile fracture morphology of TiAl alloy specimens exhibits quasi cleavage fracture characteristics. By optimizing the scanning strategy and assisting with subsequent heat treatment, it is expected to improve the uniformity of alloy structure and the anisotropy of mechanical properties.