Mechanical and hydrophobic properties of chromium carbide films via a multi-objective optimization approach

In this study, chromium carbide films are deposited on high-speed tool steel and silicon wafers using an unbalanced magnetron sputtering process. A gradient interlayer consisting of Cr/CrN/CrCN between the chromium carbide layer and substrate is prepared in order to enhance the adhesion. In the experimental design, L18 (21 × 37) orthogonal array experiments were used for the statistical purpose and the eight process control factors selected in order to study their contributions to the properties of carbide films. The mechanical and hydrophobic properties were evaluated by means of the coefficient of friction (CoF) and water contact angle (WCA), respectively. For optimizing and balancing the performance of these two properties, a grey relational analysis is applied to combine the two signal-to-noise ratios of self property in a performance index. With the grey Taguchi multi-objective optimization (GTMO) approach, the optimal experimental parameters can be determined and the verification experiments carried out. A comparison of the integrated performance index between the initial and the optimal conditions shows that the magnitude increases from 0.38 to 0.87. For film properties, the CoF decreased from 0.656 to 0.234, and the WCA increased from 83.2 to 96.3°. The gain for integrated performance index by the GTMO from the initial condition is reported as 49% positive.