Hf–Mo–Si–B Oxidation-Resistant Coatings Produced by Magnetron Sputtering in DCMS and HIPIMS Modes

This paper reports on the development of oxidation-resistant coatings in the Hf–Mo–Si–B system. We address issues pertaining to the fabrication of a functionally graded target for subsequent direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HIPIMS), analysis of the gas discharge plasma, structural characterization of the coatings, investigation of their mechanical properties, and assessment of their high-temperature oxidation resistance. The results demonstrate that the working layer of the target, produced by self-propagating high-temperature synthesis and hot pressing, has a uniform structure and contains the following phases (wt %): o-HfSi2, 32; h-HfB2, 19; t-MoSi2, 17; c-HfB, 2; m‑HfSiO4, 9; c-Si, 21. Between the working and supporting layers of the target is located chromium silicide, ensuring strong bonding between them and making it possible to successfully use the functionally graded target in both DCMS and HIPIMS, a high-energy process. The coatings we produced are X-ray amorphous and have a dense microstructure with low defect density and uniform depth profiles of their constituent elements. All of the coatings offer high oxidation resistance at temperatures of 1100 and 1300°C. The protective properties of the coatings were shown to be due to the formation of t-HfSiO4 and m-HfO2 nanocrystallites located in the Si : B : O-based oxide layer. Switching from DCMS to HIPIMS mode led to a decrease in the thickness of the oxide layer by a factor of 3–5 at temperatures of 1100 and 1300°C and helped reduce the surface defect density. The coating grown by HIPIMS at an average/peak power of 1/50 kW exhibited the highest thermal stability and good 1500°C oxidation resistance.