Oxidation resistance and thermal stability of (MoZrHfTaNb)-Si-B coatings deposited by HIPIMS method with different Ar pressure

Abstract

The influence of argon pressure on the structure, mechanical characteristics, oxidation resistance, and thermal stability of (MoTaNbZrHf)-Si-B coatings deposited by HIPIMS method using a composite target based on high-entropy (MoZrHfTaNb)Si2 silicide and (MoZrHfTaNb)B2 boride was studied. Coatings deposited at Ar pressure of 0.1–0.2 and 1.3–2.2 Pa had a dense, defect-free structure. Increasing the Ar pressure to 37–42 Pa led to the formation of a coating with a columnar structure, while, according to X-ray diffraction and transmission electron microscopy, all coatings were amorphous. Increasing the Ar pressure from 0.1 to 0.2 to 37–42 Pa led to a magnifying the growth rate of coatings in 2.5 times. All coatings were characterized by a similar hardness of 14–15 GPa. The elastic modulus and elastic recovery decreased from 196 to 178 GPa and from 40 to 34 % when the argon pressure increased from 0.1 to 0.2 to 37–42 Pa, respectively. The coatings successfully resisted oxidation at temperatures of 1100 °C and 1300 °C. The protective properties of the coatings are due to the formation of a dense oxide film based on a-Si:B:O amorphous phase with crystallites of the m-HfO2, m-ZrO2, m-Nb2O3, o-Ta2O5, t-ZrSiO4 and t-HfSiO4 phases. Heating in a TEM column showed that the coating deposited at an Ar pressure of 0.1–0.2 Pa crystallizes immediately upon reaching a temperature of 700 °C with the release of predominantly the h-MoSi2 phase. Crystallization of the coating obtained at an Ar pressure of 37–42 Pa also occurs at 700 °C, but only during long-term exposure and is accompanied by the precipitation of the h-Ta5Si3 and t-Nb5Si3 phases. Thus, it has been shown that by increasing the gas flow rate, the productivity of sputtering in the HIPIMS mode can be increased without a significant loss in hardness, oxidation resistance and thermal stability of coatings.