Evaluation of some mechanical properties of SiC films deposited on steel by plasma-assisted chemical vapour deposition from tetramethylsilane

Deposits of SiC with various Si:C atomic ratios were obtained. The growth rates are high and their variations are explained in terms of competition between different mechanisms. The hardness and adherence measured by scratch testing are a strong function of the coating composition. Hardness values at infinite loads were determined by a correction method. They range from 2300 to 3500 kgf mm -2 with an excess of silicon; conversely a few per cent of free carbon drastically lowers the hardness. Stresses were evaluated by radii curvature measurements. The variation of “normalized critical load” can be explained by an energy balance only if an energetic term of cohesive failure is introduced. Although the L c values are low, adherence is good and goes through a maximum when the Si:C ratio reaches 1.2.