Optimizing hydrophobic and wear-resistant properties of Cr–Al–N coatings

Abstract

The objective of this study is to develop a hydrophobic and wear-resistant Cr–Al–N coating. The Cr–Al–N coatings were deposited in Ar/N2 plasma using the reactive magnetron sputtering process. The hydrophobic and wear-resistant properties of the coatings were evaluated by means of the water contact angle (WCA) measurement and ball-on-disk tests, respectively. As for the experimental design, L18 (21×37) orthogonal array experiments were used for statistical purposes to optimize the deposition parameters. Eight process control factors were selected to study their contributions to the hydrophobic and wear-resistant properties of Cr–Al–N coatings. For optimizing and balancing the performance of the hydrophobic and wear-resistant properties, a gray relational analysis is applied to combine the two signal-to-noise ratios of the intrinsic properties in a performance index. The optimal experimental parameters can be determined. The properties of the Cr–Al–N coatings with the optimized parameters show that the WCA of the coatings increases from 64.7° to 100.1°, while the wear rate decreases from 3.67×10−5 to 2.38×10−5mm3N−1m−1. The gray relational grade increases from 0.40 to 0.79. This indicates that the gain for the multiple performance index is 39% positive. The Cr–Al–N coatings deposited at the optimized parameters were further annealed at evaluated temperatures to investigate the thermal effect on the Cr–Al–N coatings. The experimental results show that the Cr–Al–N coatings possess hydrophobic properties after annealing below and at 800°C. With annealing temperatures greater than 900°C, the coatings become hydrophilic and the WCA is only 45° after annealing at 1100°C.