RESIDUAL-STRESS AND MICROHARDNESS OF DLC MULTILAYER COATINGS

The residual stress and microhardness of diamond-like carbon (DLC) mul tilayer coatings (about 2.5 mu m thick), prepared by unbalanced magnet ron sputtering with various methane gas flow rates, substrate bias vol tages and substrate bias ion current densities, have been measured. Th e experimental results show that the residual stress value is strongly affected by the substrate bias voltage and ion current density. The r esidual stress value increases with substrate bias voltage, reaches a maximum of 8.5 GPa at a bias of -150 V, and then decreases slightly. H owever, at a constant bias voltage of -80 V, the residual stress incre ases with bias ion current density in the range studied here, and reac hes 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.