Regulating sublayer Cu distribution in TiAl(Cu)N coating by periodic modulation of Cu target current for enhanced erosion-corrosion resistance

Nanoscale chemical distribution in multicomponent coatings plays a key role in the microstructure and properties, but it is challenging to be precisely controlled under non-equilibrium and dynamic sputtering conditions. In this study, the Cu distribution in TiAl(Cu)N coatings has been investigated by different “tricycle” periodic modulation of Cu target current including constant-mode (G1), decreasing-mode (G2) and increasing-mode (G3). A “composition deviation” phenomenon has been observed in all coatings due to the hysteresis of plasma build-up, target poisoning, re-sputtering and inter-diffusion of deposited Cu atoms under non-equilibrium and dynamic conditions. In contrast to G1 and G3, G2 displays lower and more uniform Cu distribution, which leads to simultaneous improvement in hardness, fracture toughness, and corrosion resistance. Therefore, G2 exhibits the superior 36 h erosion-corrosion resistance (i.e., 4.2 times that of G1 and 1.6 times that of G3). This study not only illustrates the importance of “composition deviation” during coating alloying in nanoscale, but also provides a new target current periodic modulation approach to regulate the chemical composition distribution and achieve improved erosion-corrosion resistance of multicomponent coatings.