High-temperature tribological properties of (TiZrNbMoTa)N and (TiZrNbMoTa)CN ceramic coatings

Abstract

As dry-cutting tool coatings, high-entropy ceramics (HECs) exhibit excellent hardness, toughness, and wear resistance properties. However, the hardening mechanism of HEC coatings and their mechanical and frictional properties under high-temperature conditions have not been studied. In this study, we successfully prepared (TiZrNbMoTa)N high-entropy nitride (HEN) and (TiZrNbMoTa)CN high-entropy carbon nitride (HECN) coatings using reactive magnetron sputtering technology. The strengthening mechanism and thermodynamic properties of HEN and HECN coatings were systematically studied using the Debye-Grüneisen quasi-harmonic approximation model combined with density functional theory (DFT) calculations. At room temperature (RT, 25 °C) and high temperature (HT, 500 °C), the microhardness of HECN is 62 % and 56 % higher than that of HEN, respectively. Especially at RT, the microhardness of HECN reaches 46.37 GPa. Through in-situ XRD, in-situ nanoindentation, and high-temperature friction and wear analysis, we conducted in-depth research on the phase stability, high-temperature mechanical properties, and high-temperature tribological properties of HECs coatings in high-temperature. XRD test results show that HEN and HECN coatings exhibit a single-phase FCC structure and maintain good stability under HT. DFT calculation results show that the M − C bond in HECN is stronger than the M − N bond in HEN, which is why the HECN coating is harder. At HT, the wear rate of HECN coating is only reduced by 10 % compared with HEN coating. Different from RT, under high-temperature conditions, the primary wear mechanism of the coating is oxidative wear. The coating's red hardness and friction coefficient (COF) have a limited impact on the coating's high-temperature anti-wear performance. This research provides a theory and technical basis for designing and preparing protective coatings with high hardness and low friction coefficient.