Correlation of microstructure with hardness and wear resistance in (TiC, SiC)/stainless steel surface composites fabrica
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Correlation of Microstructure with Hardness and Wear Resistance in (TiC,SiC)/Stainless Steel Surface Composites Fabricated by High-Energy Electron-Beam Irradiation EUNSUB YUN, YONG CHAN KIM, SUNGHAK LEE, and NACK J. KIM Stainless-steel-based surface composites reinforced with TiC and SiC carbides were fabricated by high-energy electron beam irradiation. Four types of powder/flux mixtures, i.e., TiC, (Ti C), SiC, and (Ti SiC) powders with 40 wt. pct of CaF2 flux, were deposited evenly on an AISI 304 stainless steel substrate, which was then irradiated with an electron beam. TiC agglomerates and pores were found in the surface composite layer fabricated with TiC powders because of insufficient melting of TiC powders. In the composite layer fabricated with Ti and C powders having lower melting points than TiC powders, a number of primary TiC carbides were precipitated while very few TiC agglomerates or pores were formed. This indicated that more effective TiC precipitation was obtained from the melting of Ti and C powders than of TiC powders. A large amount of precipitates such as TiC and Cr7C3 improved the hardness, high-temperature hardness, and wear resistance of the surface composite layer two to three times greater than that of the stainless steel substrate. In particular, the surface composite fabricated with SiC powders had the highest volume fraction of Cr7C3 distributed along solidification cell boundaries, and thus showed the best hardness, high-temperature hardness, and wear resistance.
I. INTRODUCTION
PROCESS techniques such as ceramic coating or joining have been applied generally to improve surface properties of metals, in which better performance can be achieved than in metals by taking advantage of the favorable properties of ceramics.[1–4] However, when these materials are repeatedly exposed to severe conditions of high temperature, impact, and corrosive environment, fracture or separation occurs at interfaces between the metal and ceramic, and causes problems during actual applications. In response to these problems, studies have been made to obtain the desired surface compositions and microstructures by using a laser beam on ceramics such as TiN, TiC, and SiC.[5,6,7] Recently, new attempts have been made by direct irradiation using a high-energy electron beam to achieve surface hardening or surface compositing.[8–11] When a high-energy electron beam irradiates on the material surface, the kinetic energy of electrons is converted to heat. This thermal energy can readily melt ceramics having high melting points.[12,13,14] Upon irradiation on evenly deposited ceramic powders on the surface of the metal substrate, ceramic powders and part of the substrate are melted, and the ceramic elements are dispersed and penetrate into the substrate. During this process, ceramic/metal surface composites can be fabricated. Pores or cracks are rarely developed inside the composites because heating and cooling occur homogeneously.[15] EUNSUB YUN, Research Assistant, and YONG CHAN KI
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