Compression Property, Deformation Behavior, and Fracture Mechanism of Additive-Manufactured Ti-6Al-4V Cellular Solid wit
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ADDITIVE manufacturing (AM) is a versatile method for fabricating materials with complex three-dimensional geometry and designed pore characteristics.[1–3] Both nearly fully-dense materials and high-porosity cellular materials can be built by AM layer-by-layer. Powder bed fusion (PBF) with a laser beam or electron beam as the heating source is the dominant technique for AM metallic materials.[4–9] Among the AM metallic materials, Ti-based alloys, particularly Ti-6Al-4V, are promising materials for various applications and have been widely produced and studied.[8–18] The mechanical properties and fracture behaviors of AM cellular Ti-6Al-4V are dominantly controlled by the type of lattice and the porosity. Several unit cell designs, MING-WEI WU, JHEWN-KUANG CHEN, PO-HSING CHIANG, PO-MIN CHANG, and MO-KAI TSAI are with the Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, No. 1, Sec. 3, ZhongXiao E. Rd., Taipei 10608, Taiwan. Contact e-mail: [email protected] Manuscript submitted January 15, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
including cubic, diamond, rhombic dodecahedron, truncated cuboctahedron, and G7, have been extensively investigated.[18–21] Li et al.[19] investigated the effects of cell shapes (cubic, rhombic dodecahedron, and G7) on the compression properties of electron beam melted (EBM) Ti-6Al-4V cellular solid. They found that the compressive strength and deformation behavior are dominated by the bending and buckling mechanisms during loading. The cubic lattice, deformed mainly by the buckling mechanism, possesses a higher compressive strength and Young’s modulus than do the rhombic dodecahedron and G7 lattices, and it exhibits brittle crushing failure. In contrast, the G7 mesh, deformed in a high bending component, exhibits ductile characteristics under compressive stress. A unit cell with a higher strength presents lower ductility.[19] It is difficult to create a cellular alloy with both high strength and high ductility. In addition to the design, several other factors of a unit cell, including orientation,[15] strut thickness,[22] and cell size,[23] also influence the mechanical properties and fracture mode of AM cellular alloys. Weibmann et al.[15] found that the unit cell orientation dominantly changed the compression performance of selective laser melted (SLM) Ti-6Al-4V lattice. The elastic modulus and compressive strength ranged from 4.6 to 26.3 GPa and
from 128 to 403 MPa, respectively, depending on the orientation of the unit cell. Choy et al.[22] investigated the influences of the strut thickness of cubic and honeycomb unit cells on the compression properties and fracture modes of SLM Ti-6Al-4V cellular material. They found that increasing the strut thickness shifted the deformation behavior from layer-by-layer fracture to diagonal crack failure. Moreover, some studies have shown that the mechanical properties of porosity-graded AM cellular metallic materials are better than those of their counterparts with uniform porosity.[24
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