Influence of pore structure on mechanical properties of 3D printing porous tungsten
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摘要:
利用ANSYS有限元软件设计了正方体和三棱锥两种孔隙结构的多孔钨。研究发现，当分别承受点、线和面载荷时，正方体和三棱锥骨架单元受力不均匀。当骨架单元分别承受面和线载荷时，有支撑的棱柱处应力较小，没有支撑的棱柱处应力较大，并引起了较大的变形量。当骨架单元承受点载荷时，其应力和变形量均在加载处最大。采用选区激光熔化技术制备两种孔隙结构的高孔隙率多孔钨，分析了孔隙形状和尺寸对其力学性能的影响。结果表明，两种多孔钨的宏观形貌与其设计结构无明显差别，由于骨架棱柱（边）上易悬垂和粘粉导致孔隙率较设计值有所降低。预设孔隙率为50%和80%的正方体多孔钨抗拉强度分别为127.4 MPa和55.8 MPa，抗压强度分别为667.1 MPa和213.0 MPa，冲击韧性分别为6.764 J/cm2和4.492 J/cm2，硬度值相差不大。预设50%和80%孔隙率的三棱锥多孔钨抗压强度分别为231.1 MPa和65.3 MPa，冲击韧性均为2.030 J/cm2，硬度与正方体骨架相同。正方体和三棱锥多孔钨的拉伸和压缩断口形貌均呈现出典型的准解理脆性断裂特征。
Abstract:The porous tungsten with the cube and triangular pyramid shape was designed by ANSYS finite element analysis in this paper. In the results, when the point, line, and plane loads are applied, respectively, the stress on the cube and triangular pyramid skeleton units is uneven. When the skeleton unit is subjected to the plane and line loads, respectively, the stress at the supported struts is relatively small, while the stress at the unsupported struts is relatively large, causing a large amount of deformation. When the skeleton unit is subjected to the point load, the stress and deformation are both the maximum at the loading point. The porous tungsten in the shape of cube and triangular pyramid with high porosity was fabricated by selective laser melting (SLM) technique, and the effects of pore shape and size on the mechanical properties were investigated. The results show that the macrostructure of these skeleton structure is not significantly different from the designed structure, but the porosity is lower than that of the designed value, because of the hanging and sticky powders on the skeleton struts. The tensile strength of cube skeleton with 50% and 80% porosity is 127.4 MPa and 55.8 MPa, the compressive strength is 667.1 MPa and 213.0 MPa, the impact toughness is 6.764 and 4.492 J·cm−2. The compressive strength of the triangular pyramid skeleton with 50% and 80% porosity is 231.1 MPa and 65.3 MPa, the impact toughness is 2.030 J·cm−2, and the hardness is similar as that of the cube skeleton. The tensile and compressive fracture morphology of the cube and triangular porous tungsten show the typical quasi-cleavage brittle fracture.
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Keywords:
- porous tungsten /
- pore structure /
- finite element /
- microstructure /
- mechanical properties
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图 1 多孔骨架单元结构示意图：（a）正方体骨架单元；（b）三棱锥骨架单元
Figure 1. Schematic of the porous skeleton units: (a) cube skeleton unit; (b) triangular pyramidal skeleton unit
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图 2 不同单元结构网格划分：（a）正方体单元；（b）三棱锥单元
Figure 2. Meshing for the different cells: (a) cube; (b) triangular pyramid
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图 3 正方体骨架单元在不同加载模式下有限元分析应力和变形量分布云图：（a）应力，面加载；（b）变形量，面加载；（c）应力，线加载；（d）变形量，线加载；（e）应力，点加载；（f）变形量，点加载
Figure 3. Stress and deformation distribution in finite element analysis of the cube skeleton unit under different loading modes: (a) stress, plane loading; (b) deformation, plane loading; (c) stress, line loading; (d) deformation, line loading; (e) stress, point loading; (f) deformation, point loading
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图 4 三棱锥骨架单元在不同加载模式下有限元分析应力和变形量分布云图：（a）应力，面加载；（b）变形量，面加载；（c）应力，线加载；（d）变形量，线加载；（e）应力，点加载；（f）变形量，点加载
Figure 4. Stress and deformation distribution in finite element analysis of the triangular pyramid skeleton unit under different loading modes: (a) stress, plane loading; (b) deformation, plane loading; (c) stress, line loading; (d) deformation, line loading; (e) stress, point loading; (f) deformation, point loading
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图 5 钨粉显微形貌及其多孔骨架设计结构图：（a）钨粉显微形貌；（b）三棱锥骨架，孔隙率50%；（c）正方体骨架，孔隙率80%
Figure 5. Microstructure of W powders and the porous skeleton models: (a) microstructure of W powders; (b) triangular pyramid skeleton with 50% porosity; (c) cube skeleton with 80% porosity
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图 7 多孔钨骨架宏观和表面显微形貌：（a）正方体骨架宏观图；（b）、（c）正方体骨架，沿打印方向；（d）三棱锥骨架宏观图；（e）、（f）三棱锥骨架，垂直打印方向
Figure 7. Macrographs and SEM images of the porous W skeleton: (a) macrographs of cube skeleton; (b), (c) cube skeleton parallel to the print direction; (d) macrographs of triangular pyramid skeleton; (e), (f) triangular pyramid skeleton perpendicular to the printing direction
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图 8 多孔钨不同方向金相形貌：（a）沿打印方向；（b）垂直打印方向
Figure 8. Metallographic morphology of the porous W: (a) parallel to the print direction; (b) perpendicular to the printing direction
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图 9 不同孔隙三棱锥和正方体孔形状多孔钨的拉伸和压缩应力应变曲线：（a）拉伸；（b）压缩
Figure 9. Stress-strain curves of the cube and triangular pyramid porous W under different porosity: (a) tensile; (b) compressive
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图 10 多孔钨断口形貌：（a）、（b）冲击实验；（c）、（d）压缩实验；（e）、（f）拉伸实验
Figure 10. Fracture morphology of the porous W: (a), (b) impact test; (c), (d) compressive test; (e), (f) tensile test
密度 / (g·cm−3) 泊松比 弹性模量 / MPa 体积模量 / MPa 剪切模量 / MPa 19.5 0.28 4.1000 ×1053.1136 ×1051.6055 ×105
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表 2 选区激光熔化制备多孔钨工艺参数
Table 2 Process parameters of the porous tungsten skeleton prepared by SLM
激光功率 / W 扫描速度 / (mm·s−1) 铺粉层 / μm 扫描间距 / μm 光斑直径 / μm 300 450 25 60 100
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表 3 正方体骨架和三棱锥骨架实测孔隙率、硬度和冲击韧性
Table 3 Measured porosity, hardness, and impact toughness of the cube and triangular pyramid skeleton
孔隙结构 设计空隙率 / % 测量孔隙率 / % 硬度，Hv 冲击韧性 / (J·cm−2) 正方体骨架 50 22.05 468.9 6.764 80 57.10 472.8 4.492 三棱锥骨架 50 53.68 473.7 2.030 80 73.79 471.3 2.030
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