Elevated temperature oxidation of laser surface engineered composite boride coating on steel
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I. INTRODUCTION
TITANIUM diboride is a low density, hard ceramic material with excellent wear, abrasion, and oxidation resistance until 1273 K.[1,2] Also, it is chemically inert in corrosive environments, which makes it an excellent coating material for a variety of applications such as cutting and mining tools, wire drawing dies, energy conversion equipment, and aluminum extraction in the Hall–Heroult cell.[3,4] However, there is not enough evidence available in the literature to confirm the aforementioned fact. Additionally, there are very few studies available on the oxidation behavior of TiB2 ceramic.[5–9] Due to inconsistency in the nature of the sample and analysis, these studies contradict themselves and do not provide sufficient conclusive information about oxidation behavior of TiB2. Moreover, all of these oxidation studies were performed on monolithic material that is different from the coating of composite nature. It is, therefore, essential to evaluate the high-temperature oxidation behavior of the composite TiB2 coating. TiB2 is a refractory ceramic, which can be deposited on various metallic substrates using several processes such as physical and chemical vapor deposition,[10] thermal spray,[11] pulsed electrode surfacing,[3,12,13] and laser surface modification.[3,14] Each of these processes has its own limitations and characteristics that result in different coating morphology and composition. Hence, properties of TiB2 coating vary with the change in deposition process. This further stresses the need of evaluating the properties of TiB2 coating as a function of deposition process. In the present study, TiB2 has been deposited on AISI 1010 steel using a laser surface engineering (LSE) technique. ARVIND AGARWAL and LALITHA R. KATIPELLI, Graduate Research Assistants, and NARENDRA B. DAHOTRE, Professor of Materials Science and Engineering, are with Department of Materials Science and Engineering, Center for Laser Applications, University of Tennessee Space Institute, Tullahoma, TN 37388. Manuscript submitted April 27, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
Laser surface engineering provides several advantages over other processes. Laser processing is a nonequilibrium process that involves high cooling rates (103 to 108 K/s), producing metastable phase(s) and a wide variety of microstructures with novel properties that cannot be produced by any conventional processing technique.[15] Moreover, the surface structure can be further tailored to the desired requirements by varying process variables such as laser traverse speed, power, beam size and type, and precursor composition.[16,17] Coatings deposited using lasers are metallurgically bonded providing a sound and adherent interface between the coating and substrate.[17,18] The present study discusses the elevated temperature oxidation behavior of a composite TiB2 coating deposited on AISI 1010 steel using Nd:YAG laser. A detailed qualitative investigation is carried out with respect to changes in coating morphology, oxide scale formation and m
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