Correlation of Microstructure with Wear and Fracture Properties of Two-Layered VC/Ti-6Al-4V Surface Composites Fabricated by High-Energy Electron Beam Irradiation

摘要

Resistance to wear, oxidation, and corrosion of materials largely depends on the composition and microstructure of the material surface, and properties required for the surface may be different from those of bulk substrates in many instances. For enhancement of surface properties, researches have been undertaken using direct irradiation of high-energy beams such as a pulsed-laser beam or electron beam to harden the surface or to make surface composites. Recently, there are many active researches on the fabrication of surface hardened materials or surface composites using a high-energy electron accelerator (several MeV energy range) Studies on surface composites have mainly focused on improvement of wear properties, microstructural modification, and their high-temperature application. In the case of titanium alloys, however, the thickness of surface composites which can be fabricated by one time electron beam irradiation is relatively thin (about 1 mm), and their microstructures are varied with thickness, thereby limiting the enhancement of mechanical properties. It is thus highly required to form thicker surface composite layers with homogeneous microstructure. In the present study, surface composites with enhanced hardness and wear resistance were fabricated by depositing VC powders on a Ti-6Al-4V substrate and irradiating them with a high-energy electron beam. In order to thicken the surface composite layer and to obtain homogeneous microstructure, a two-layered surface composite was fabricated by repeating the electron beam irradiation process, and its microstructure, hardness, and wear resistance were analyzed in comparison with those of an one-layered surface composite fabricated by one time electron beam irradiation. Also, effects of the size and volume fraction of ceramic particles on fracture properties of surface composites were investigated by in situ fracture test.