Microstructure of TiB 2 /carbon steel surface-alloyed materials fabricated by high-energy electron beam irradiation
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I. INTRODUCTION
PROCESS techniques such as laser cladding, chemical vapor deposition,[2] cathodic arc ion plating,[3] dynamic ion mixing,[4] and sputtering[5] have been applied to improve the surface properties of metals. Better performance can be achieved in ceramics than in metals by taking advantage of the favorable properties of ceramics such as excellent resistances to heat, corrosion, and abrasion. However, when these materials are repeatedly exposed to severe conditions of high temperature, impact, and corrosive environment, fracture or separation occurs in the interfaces between metal and ceramic. In response to these problems, work has been performed to obtain the desired surface compositions and microstructures by using laser beams on ceramics such as TiN[6,7] and TiC.[8] Recently, a new processing method has been introduced by irradiating accelerated high-energy electron beams directly on the material in air.[9–14] When a high-energy electron beam is irradiated on the material surface, the high kinetic energy of electrons is momentarily converted to high thermal energy by forming phonons as electrons strike the lattice. This thermal energy can easily melt ceramics with high melting points. 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 penetrated into the substrate. During this process, ceramic/metal surface-alloyed materials can be fabricated. The electron beam irradiation method has a good thermal efficiency, about twice that of laser beams. Pores or cracks are rarely developed inside the materials because heating and cooling are done homogeneously. Due to the short irradiation [1]
KWANGJUN EUH, Research Assistant, and SUNGHAK LEE, Professor, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784 Korea. KEESAM SHIN, Assistant Professor, is with the Department of Metallurgy and Materials Science, Changwon National University, Changwon, 641-773 Korea. Manuscript submitted April 2, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
time, surface oxidation and intrusion of inclusions can be prevented. Because the work is performed in air, a continuous process is possible and a wide area can be treated at one time. Thus, this method is advantageous to process largescale materials in mass production. In the present study, surface-alloyed materials with improved surface properties were processed by depositing TiB2 powders on the surface of a plain carbon steel substrate and by irradiating high-energy electron beam. TiB2 powders have high hardness and excellent resistances to high temperature, abrasion, and corrosion. Because of their stability at high temperatures, with a melting point of about 3225 8C 6 20 8C,[15] TiB2 powders are widely used in antiabrasion coating for tools and in coating of aerospace materials to enhance high-temperature properties. Figure 1 is a scanning electron microscope (SEM) microgra
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