Abstract
Carbide coatings have been used to enhance the lifetime service of molds used for hot and cold forging, extrusion and powder metallurgy which are subjected to abrasive forces. Thermal reactive diffusion (TRD) process via molten salt bath is one of the coating processes suitable for the mentioned applications. The process has many advantages including excellent adhesion to the substrate as well as cost efficiency over other similar surface coating methods. The novelty in this research is the formation of hard carbide coatings using two separate oxide baths containing chromium oxide (Cr2O3) and vanadium oxide (V2O5). The coatings were produced on W1 tool steel by using TRD method via molten salt baths at 1000 °C for 8, 10 and 12 h, respectively. Phase structure, composition and microstructure of the coatings were analyzed by scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), and X-ray diffraction (XRD). The hardness of the coatings was evaluated by micro-indentation test. The results showed that chromium carbide and vanadium carbide coatings are formed successfully on the substrate with chemical formula Cr7C3 and VC, respectively. Vanadium carbide layer showed higher hardness (1854 HV) relative to the chromium carbide layer (1782 HV). However, its thickness (16 μm) was relatively lower than that of the chromium carbide layer (20 μm) after similar immersion time of 12 h. Moreover, it was found that, while the coating thickness increases with time, there is a specific time to reach the optimum thickness for each type of coatings.
Published Version
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