Optimization of coating parameters for duplex treated AISI 5140 steel

The AISI 5140 steel was TiN coated with duplex treatment (ion nitriding + physical vapor deposition, PVD). Discharge current, substrate bias, coating pressure, and substrate type were chosen to be the coating parameters and three levels for each parameter were determined. After duplex treatment, the aim is to minimize wear rate and friction coefficient and to maximize coating hardness. While the optimum conditions were determined, due to existence of more than one goal, the trade-off among goals was considered. First of all, each goal was optimized separately, and then all the goals were optimized together, considering the priority of the goals. When all the goals were taken into account together, the optimum results were obtained at a pressure of 0.4 Pa, at a current of 4 A and for a substrate bias of 70 V on a substrate polished and H2 sputter etched after ion nitriding.