电子束熔丝增材制造TC11钛合金组织及力学性能

采用电子束熔丝增材工艺制造了直径260 mm的试环。分析了不同热处理状态的增材制造TC11钛合金微观组织和室/高温拉伸性能及其各向异性。并测试分析了锻件基体晶粒2次热处理和锻件基体与增材界面处的组织和性能。结果表明：沉积态微观组织为沿<001>β方向生长的柱状晶。晶界存在连续α相,晶体内部由集束和网篮α相组成的片层组织。经950℃/2h/空冷+530℃/6h/空冷的热处理后晶界连续α相破碎,晶内α相宽度从1.1μm增加至1.8μm。并形成具有二次α相的双片层组织。锻件与增材过渡区锻件一侧,等轴初生α相转变为“雪花”状初生α相。锻件基体2次热处理后等轴初生α相轮廓光滑,转变β相比例增加,并形成大量细小的针状二次α相。沉积态室温及500℃高温拉伸性能均具有明显的各向异性。经过热处理后室/高温拉伸性能均获得改善并高于锻件要求且各向异性明显降低。与沉积态相比,热处理态室温抗拉强度和断后伸长率各向异性分别从4.4%和27.1%降低至1.6%和5.4%。柱状晶及其晶界连续α相是引起塑性各向异性的原因。锻件+增材界面处热处理后其室/高温拉伸性能均满足锻件要求。

Microstructure and Mechanical Properties of TC11 Titanium Alloy Fabricated by Wire-feed Electron Beam Additive Manufacturing

In this study, a α+β high-temperature titanium alloy TC11 ring (f260 mm) was fabricated by wire-feed electron beam additive manufacturing (EBAM). The microstructure, tensile property and the anisotropy of the tensile properties of the fabricated alloy were investigated. The microstructure and tensile property of the wrought alloy and the wrought + additive manufacturing interface were also evaluated. Optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction were employed to study the microstructure characteristics. The tensile properties along the vertical (V) and horizontal (H) directions were evaluated at both room temperature and 500 ℃. Results indicated that the microstructure of the as-built alloy was characterized by coarse columnar grains, lamellar α (colony and basket-weave), and the continuous grain boundary α. The prior β grains had a strong <001>_βtexture along the grain growth direction. Compared to the as-built alloy, the lamellar α phase was coarsened from 1.1 μm to 1.8 μm, the discontinuous grain boundary α and bi-lamellar α phase formed by post-deposition heat treated at 950 ℃/2 h/AC+530 ℃/6 h/AC. The equiaxed primary α of the wrought substrate alloy changed from globular to snowflake near the interface. After heat treatment, the volume fraction of the transformed β decreased for the wrought substrate alloy. In terms of tensile properties, the vertical specimens exhibited lower strength but higher ductility than the horizontal specimens at both room and elevated temperatures. The anisotropic elongation results from the directional columnar prior β grains and continuous grain boundary α phase, which facilitated the intergranular cracking. The tensile strength and ductility were simultaneously enhanced by the heat treatment to meet the standard requirements for wrought counterparts. Moreover, the anisotropy of the tensile strength and elongation for the post-deposition heat treated alloy was decreased significantly from 4.4% and 27.1% to 1.6% and 5.4%, respectively, in comparison to the as-built alloy. The tensile property of the wrought+additive manufacturing interface can meet the standard requirements for wrought counterparts.