Effects of duty cycle and pulse frequency on the fabrication of AlCrN thin films deposited by high power impulse magnetron sputtering

Abstract

High power impulse magnetron sputtering (HIPIMS) is a newly developed coating technology, characterized by its ultra-high peak current and peak power density to achieve unique thin film properties, such as high hardness, good adhesion and tribological performance. In this study, an AlCr alloy target was used to deposit AlxCr1−xN coatings on various substrates by the HIPIMS technique. The aim of this work was to systematically study the microstructure evaluation and mechanical properties of AlxCr1−xN coatings as a function of duty cycle and pulse frequency. The experimental results showed that the peak power density increased linearly as the duty cycle decreased from 5% to 2% at constant frequency of 1000Hz. A maximum peak power density of 2.76kWcm−2 was achieved at the duty cycle of 2% and repetition frequency of 833Hz. A mixture of cubic and hexagonal AlxCr1−xN phases was found for each coating. The x value of AlxCr1−xN thin films changed from 0.72 to 0.75 and showed no direct relationships with duty cycle and repetition frequency. The peak power density had great influence on the microstructure evolution and altered the microstructure from coarse columnar to fine columnar structure. Re-nucleation grains were also found between columnar grains. The hardness increased with increasing frequency at constant duty cycle of 2% and reached the optimum hardness of 39.9GPa at x=0.75. Good adhesion and wear resistance was observed for each coating. The critical load increased as the repetition frequency increased from 500 to 1250Hz at the same duty cycle of 2%. Since the wear resistance for each coating was excellent, the duty cycle and pulse frequency showed limited influence on the wear resistance of thin films.