Surface coatings have been used on steel tools for cold working in order to obtain mechanical properties superior to those obtainable with the alloy steels such as high hardness, high thermal conductivity, low friction coefficient, high mechanical resistance, and low wear rate. The purpose of this work is thin CVD diamond coatings production on steel tools, with the use of an intermediate layer of vanadium carbide (VC). We will study two forms of VC coatings: by reactive Thermodiffusion process (TD or TRD, from the English Thermoreactive Diffusion) and by laser cladding. The TRD process consists in steel surface thermal activation with substrate immersed in a molten salt, at temperatures between 900 ° C and 1050 ° C, allowing the formation, diffusion and metallic vanadium reaction to form stoichiometric or nearly stoichiometric VC compounds. Although it is a relatively simple process, numerous variables can interfere in the vanadium carbide formation, as the adopted thermal cycle, the proportion of the reactants and composition of the powder mixture (flux, reducing and forming), the chemical composition of the steel, the carbon concentration in the salt bath and, the oxygen presence in the system. The VC Laser cladding is a process in which a powder mixture is dispersed on the surface of a substrate and the incidence of the laser beam form a molten layer composed by the substrate and the powder. This process offers advantages over the thermodiffusion as reduced time and low cost. However, it demands high technology. The purpose of this proposal is to obtain through both techniques uniform intermediate layers and sufficient thickness to inhibit migration of the substrate iron atoms to the surface and alleviate the residual stress resulting tool contraction during cooling from the CVD diamond growth temperature. This work aims to obtain CVD diamond thin films with high adhesion, using intermediate VC coatings, suitable for applications in tools for metal cutting and plastic deformation.
News published in Agência FAPESP Newsletter about the scholarship: