Processing of hardmetal coatings on steel substrates

The potential to apply WC-Co based hardmetal coatings on steel substrates by means of electrophoretic deposition and subsequent hybrid microwave heating is reported. Crack-free WC-Co powder layers with a green density of 43 % were deposited on cylindrical carbon steel, stainless steel and high speed steel substrates from an acetone-based suspension. The thickness of the green hardmetal coating could be precisely controlled by the EPD process. Moreover, EPD of coatings is a very fast processing technique with processing times below 10 seconds. Fast firing procedures established by means of hybrid microwave heating allowed full densification of the coatings, with a sintered thickness up to 200 gm. Microstructural investigation revealed a gradient concentration profile in the densified coating, caused by the interdiffusion of iron and alloying elements from the substrate. Hardness measurements indicated that the coating was about 6 GPa harder than the thermally quenched steel substrate material. With a high speed steel substrate, the hardness of the coating was about 13.5 GPa.