Effect of target composition on the microstructural, mechanical, and corrosion properties of TiAlN thin films deposited by high-power impulse magnetron sputtering

Ti1−xAlxN thin films were deposited using reactive high-power impulse magnetron sputtering on silicon Si (100), tungsten carbide (WC-Co), and SUS304 substrates using three metallurgical TixAly alloy targets with Al/(Al + Ti) atomic ratios of 0.19, 0.36, and 0.57. A fixed duty cycle of 1% and a N2/Ar ratio of 15.8% was used. The current-voltage characteristics of the TixAly alloy targets were first investigated. Then, the microstructural evolution and the mechanical and corrosion properties of the as-deposited Ti1−xAlxN thin films were analysed by scanning electron microscopy, grazing incident X-ray diffractometry, X-ray photoelectron spectroscopy, transmission electron microscopy, nanoindentation, and anodic potentiodynamic polarisation tests. The power density of 1.86 kW/cm2 achieved with the square-like power output wave obtained in the constant current mode was higher than the 1.37 kW/cm2 power density obtained with the triangular-like power output wave. The deposition rates of the Ti1−xAlxN thin films increased from 13.4 to 28.6 nm/min with an increasing alloy target Al/(Al + Ti) atomic ratio due to the higher sputter yield of Al than Ti. The Al/(Al + Ti) atomic ratio of the alloy target determines the structure, which changed from a highly preferred TiN (111) orientation (Al/(Al + Ti) ratio = 0.19) to a nanocomposite structure (Al/(Al + Ti) ratio = 0.57). The nanoindentation results indicated that the highest hardness and elastic modulus values of the Ti1−xAlxN thin films were 33.3 GPa and 405.9 GPa, respectively, obtained using the Al/(Al + Ti) = 0.19 alloy target. In addition, the friction coefficients of the Ti1−xAlxN thin films were between 0.68 and 0.77. However, the potentiostatic polarisation measurements showed that the amorphous TiAlN films exhibited the highest corrosion resistance in 3.5% NaCl solution, as the corrosion resistance of the Ti1−xAlxN coatings increased as the Al/(Al + Ti) atomic ratio increased.