Effect of mid-frequency pulse insertion on the microstructural and mechanical properties of AlTiN coatings prepared using superimposed HiPIMS process

Abstract

Superimposed high-power impulse magnetron sputtering (HiPIMS) refers to the insertion of medium frequency (MF) pulses during the off-time of the pulse sequence to enhance the rate of thin film deposition. In this work, we investigated the effects of inserting MF pulses (0 to 42) on the deposition rate, microstructure, and mechanical properties of AlTiN films. Our results indicate that the current-voltage (I-V) characteristics discharging with an Al65Ti35 target were affected by the introduction of N2 reaction gas and the additional MF power output, due to an impedance change under given plasma conditions. All samples presented mixed phases of AlN and TiN based on the chemical composition and crystallographic analysis. Superimposition improved the power-normalized deposition rate from 0.034 to 0.149 nm/min.kW without a significant decline in the adhesion quality of the deposited films. Increasing the number of inserted MF pulses from 0 to 42 led to a decrease in the peak power density of HiPIMS from 1357 to 509 W/cm2 and MF from 115 to 60 W/cm2. This can be attributed to the fact that the configuration of the HiPIMS system in this study used only one DC power supply, which outputted HiPIMS and MF modes together. Increasing the number of inserted MF pulses decreased the hardness of the thin film from 23 to 15 GPa as well as the compressive stress, due to an increase in the average size of the columnar crystals. These findings demonstrate that the application of AlTiN films can greatly enhance the corrosion resistance of SUS304.