Abstract
In this study, composite coatings were fabricated by preplacing a TiC layer on H13 tool steel and surface melting with a pulsed Nd: YAG laser. Since the morphology of hard phase particles is one of the determinants of the wear properties of composite coatings, the role of process variables on the shape and size of carbide precipitates was investigated. The transverse cross-section of the laser-scanned samples was studied by an optical microscope to evaluate the geometrical changes of alloyed areas. Scanning electron microscopy and X-ray energy dispersive spectroscopy were used to probe the microstructure and chemical composition of the coating layers. X-ray diffraction was used to identify the phases. The results showed that by the partial or total dissolution of TiC particles in the melt pool, TiC-type MC carbides precipitated as the primary phase. Alterations in pulse laser variables changed the geometry of the alloyed region and hence the concentration of dissolved Ti and C elements in the composite coating. Investigation of the effect of the laser variables in the form of “effective peak power density” (EPPD) revealed that increasing the EPPD led to an increase in the Fe/Ti weight ratio in the composite. As the Fe/Ti weight ratio increased, the shape of the MC precipitates changed gradually, from fully developed dendrites to petal, and polyhedral morphology.
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