Correlation of microstructure and abrasive and sliding wear resistance of (TiC,SiC)/Ti-6Al-4V surface composites fabrica
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INTRODUCTION
NEW advanced materials developed to enhance surface properties of Ti alloys include surface composites fabricated by using high-energy heat sources such as a laser beam and electron beam.[1–7] Surface compositing is a fabrication method in which wear resistance, corrosion resistance, and thermal resistance can be enhanced by depositing desired elements on a substrate to form a composite layer. This method not only contributes to the development of new materials having excellent properties, but it also reduces production costs by compositing the surface only when fabricating alloys that require high-priced elements. A high-energy (in the energy range of several megavolts) electron accelerator has several advantages: (1) work can be done in air, (2) the thermal efficiency is more than double that of the laser-beam method, and (3) the maximum hardening depth can extend down to several millimeters by momentarily irradiating with an extremely high energy density (104 to 105 kW/cm3).[8,9] When ceramic powders are deposited evenly on a metal surface and then irradiated JUN CHEOL OH is Postdoctoral Research Associate, Department of Materials, University of Oxford, Oxford, OX1 3PH, United Kingdom, and Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784 Korea. Contact e-mail: [email protected] SUNGHAK LEE is Professor, Center for Advanced Aerospace Materials and Department of Materials Science and Engineering, Pohang University of Science and Technology. Manuscript submitted November 6, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
by an electron beam, ceramic/metal surface composites can be fabricated as ceramic powders and substrate, are melted, and the ceramic elements penetrate into the substrate and precipitate. On surface composites are precipitated particles of high hardness such as carbides, borides, and oxides, which greatly improve hardness and wear resistance.[10] However, since they are much harder than the substrate, the matrix is selectively worn out during the wear process, resulting in protruded particles and a rougher worn surface. Some protruded particles fall off from the substrate and work as abrasive particles, thereby accelerating the wear process.[11,12] Depending on the wear modes, e.g., abrasive wear or sliding wear, the hard precipitate particles and the matrix holding the particles can play different roles in the wear process. Thus, intensive studies are required in order to see the level of hardness and the amount of precipitates that can work favorably for improved wear properties and to investigate how the wear mechanism changes with the wear mode. In this study, Ti-based surface composites with enhanced hardness and wear resistance were fabricated by depositing TiC and SiC powders on a Ti-6Al-4V substrate and irradiating them with a high-energy electron beam, and the effects of kind, size, and volume fraction of precipitates on wear resistance were investigated. By varying the ceramic powders which determine the kind and volume
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