Microtribological characterization of group V and VI metal-carbide wear-resistant coatings effective in the metal casting industry

Abstract

The molds used in metal casting and molten metal injection industrial processes can be protected with a novel thin film coating that reduces the wear of the molds after repeated usage, and greatly eases the unmolding operation. These coatings are based on the group V and VI metal carbides and are obtained by plasma assisted arc deposition from pure metal targets and argon and hydrocarbon gas mixtures. The coatings are deposited on the inner surface of the hot working steel molds, with a metal nitride thin film inter-layer. The carbide layer compositions are over-stoichiometric in carbon. These coatings have a low chemical reactivity against molten metals and they show a low friction coefficient and wear rate, these last properties being enhanced when the carbon content in the carbide layer is increased. We examine the surface mechanical properties of these coatings: hardness, friction coefficient and wear rate as measured by micro-indentation and micro-scratch analysis, and we relate these properties to the process parameters of the coating deposition. Finally, we discuss the mechanisms that may account for the notable performance of these coatings.