Mechanical and tribological properties of Ti-Al-Y-N and Ti-Al-Ta-N coatings deposited by HiPIMS: Influence of the bias voltage

Despite extensive research on PVD coatings, few studies explore the use of High-Power Impulse Magnetron Sputtering (HiPIMS) for depositing TiAlYN and TiAlTaN coatings, especially regarding the impact of bias voltage. This study focuses on a monolayer architecture to isolate the impact of substrate bias voltage on the coatings' properties. This study investigates how different substrate bias voltages (-60 V, -90 V, and -135 V) affect the chemical, morphological, mechanical, and tribological properties of these coatings. The results show that increasing the bias voltage leads to a decrease in deposition rate, roughness, and grain size, indicating greater atom mobility and film densification. Both coatings exhibited a face-centered cubic (fcc) structure. An increase in bias voltage resulted in a shift of the diffraction peaks to lower angles, a consequence of increased compressive residual stress. The coatings containing Yttrium (Y) showed a smaller grain size and higher hardness, in accordance with the Hall-Petch effect. Although the coatings containing Tantalum (Ta) were denser, they had lower hardness and resistance to plastic deformation due to their larger grain size. Toughness was optimised at -90 V, resulting in max. values of 248.9 N² for TiAlYN and 195.0 N² for TiAlTaN. The hardness of TiAlYN and TiAlTaN coatings increased 26% and 24% at higher bias voltages. Tribological tests revealed that higher bias voltages reduced the wear track depth and specific wear rates. The main wear mechanism was abrasive. The higher wear rate in the TiAlTaN coatings is due to their lower hardness and resistance to plastic deformation.