Characterization and properties of tungsten carbide coatings fabricated by SPS technique

Tungsten carbide coatings were fabricated on tungsten substrates with spark plasma sintering method by covering a layer of graphite powders on the substrates. Composition, crystalline structure, hardness, thermal conductivity and corrosion resistance of the coatings were evaluated by scanning electron microscopy, X-ray diffraction, Vickers hardness test, electrochemical impedance spectroscopy and dipping experiment. It was found that the W–C coated samples exhibit three-layer structure containing three different phases, which from the surface to the interior are hexagonal WC, hexagonal W2C and body center cubic W(C), respectively. Thickness of the total W–C coatings is about 20 μm, and closely dependent upon the holding time and sintering temperature; average hardness of the coatings was 2125 HV; thermal conductivity of both uncoated and coated samples is similar and decreases from 180 to 130 W m−1 K−1 in the temperature range of 27–500 °C. Furthermore, W–C coated samples have better corrosion resistance than that of uncoated samples in 3.5% NaCl solution or 10% nitric acid solution at room temperature.