Correlation of microstructure with wear and fracture properties of two-layered VC/Ti-6Al-4V surface composites fabricated by high-energy electron-beam irradiation |
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Authors: | Jun Cheol Oh Chang Sup Lee Sunghak Lee |
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Affiliation: | (1) the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, 790-784 Pohang, Korea;(2) the Materials Science and Engineering Department, Pohang University of Science and Technology, Korea |
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Abstract: | Correlation of microstructure with the hardness, wear resistance, and fracture toughness of two-layered VC/Ti-6Al-4V surface
composites fabricated by high-energy electron-beam irradiation was investigated in this study. A mixture of VC powders and
CaF2 flux was deposited on a Ti-6Al-4V substrate, and then an electron beam was irradiated on these powder mixtures to fabricate
an one-layered surface composite. A two-layered surface composite was fabricated by irradiating an electron-beam again onto
the powder mixture deposited on the one-layered surface composite. The composite layers of 1.2 to 1.5 mm in thickness were
homogeneously formed without defects and contained a large amount (25 to 40 vol pct) of carbides in the martensitic or β-Ti matrix. This microstructural modification, including the formation of hard carbides and hardened matrix, improved the
hardness and wear resistance. Particularly in the two-layered surface composite containing more carbides, the wear resistance
was greatly enhanced to a level 7 times higher than that of the Ti-6Al-4V substrate. In-situ observation of the fracture process showed that microcracks were initiated at carbides and propagated along these microcracked
carbides and that shear bands were formed in the matrix between these microcracks. In the two-layered surface composite, numerous
microcracks were initiated at many carbides and then rapidly propagated along them, thereby lowering the fracture toughness. |
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