Excess carbon and microhardness of vapor deposited TiC coating

TiC coatings, vapor deposited on polycrystalline steel substrates (stainless steel and low carbon steel) at 450°C, applied bias (−120 V) and various flow rates (up to 250 sccm) of C2H2, were studied by vibrational spectroscopy (FTIR) and transmission electron microscopy with regard to the identity of excess carbon. The reaction of Ti plasma with C2H2 gas at a relatively high flow rate (250 sccm) produced amorphous aromatic carbon with sp hybridizations and a finer size of TiC crystallite, consequently a relatively high Vickers hardness (3500 kg mm−2). Hydrogen was suggested to chemisorb on excess carbon and Ti-terminated TiC(111) surface. Chromium, leached from stainless steel, caused the Cr23C6 formation, hence the consumption of excess carbon in the coating.