Residual stress and microhardness of DLC multilayer coatings

The residual stress and microhardness of diamond-like carbon (DLC) multilayer coatings (about 2.5 mu m thick), prepared by unbalanced magnetron sputtering with various methane gas flow rates, substrate bias voltages and substrate bias ion current densities, have been measured. The experimental results show that the residual stress value is strongly affected by the substrate bias voltage and ion current density. The residual stress value increases with substrate bias voltage, reaches a maximum of 8.5 GPa at a bias of -150 V, and then decreases slightly. However, at a constant bias voltage of -80 V, the residual stress increases with bias ion current density in the range studied here, and reaches a maximum of 8.0 GPa at a bias ion current density of 3.0 mA cm(-2). Furthermore, a close correlation between microhardness and residual stress is observed. Increasing the methane gas flow rate to a certain value leads to higher residual stresses and microhardnesses. However, a further increase in the gas flow rate has no obvious effect.