| This study is concerned with the analysis of microstructure, hardness, wear resistance, and fracture toughnes of two-layered VC/Ti-6Al-4V surface composites fabricated by high energy electron beam irradiation. The mixture of VC powders and CaF_2 flux was deposited on a Ti-6Al-4V substrate, and then electron beam was irradiated on these powder mixture to fabricate a one-layered surface composite. A two-layered surface composite was also fabricated by irradiating electron beam again onto the powder mixture deposited on the one-layered surface composite. The composite layers of 1.2∼1.5 ㎜. in thickness were homogeneously formed without defects, and contained a large amount (25∼40 vol.%) of (Ti, V)C precipitates in the martensitic or V-rich β-Ti matrix. This microstructural modification including the formation of hard carbides and hardened matrices in the surface composite layers improved hardness and wear resistance. Particularly in the two-layered surface composite containing more carbides, the wear resistance was greatly enhanced by seven times higher than that of the Ti-6Al-4V substrate. In-situ observation of fracture process showed that microcracks were initiated at carbides and propagated along these microcracked carbides, and that in the two-layer surface composite, more microcracks were easily formed at carbides than in the one-layed composite, thereby showing lower fracture toughness. |
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