Microstructure of WC/C coatings deposited on steel substrates

Electron microscopy, including scanning (SEM), transmission (TEM) and high-resolution (HRTEM) were employed to characterise slightly different tungsten carbide/carbon coatings deposited onto steel substrates. Complementary techniques, such as X-ray diffraction (XRD), Auger electron spectroscopy (AES) and energy filtered TEM (GIF) were also used. The coatings were deposited by magnetron sputtering of pure WC and Cr targets in a plasma decomposition of C2H2 in mixed Ar-C2H2 discharges. The coatings are made up of a chromium interlayer, a coarse WC/C intermultilayer, a WC layer, and the WC/C multilayer. The chromium interlayer has a body centred cubic phase and a dense columnar structure, while the remaining coating is truly amorphous, with the exception of polycrystalline particles and clusters that are present within some layers. Crystalline particles and clusters were identified as having the cubic beta -WC1-x phase. Defects in the coatings were also found, due to substrate surface irregularities and to the growth structure of the chromium columns.