Thermal stability and high-temperature oxidation behavior of Si–Cr–N coatings with high content of silicon

Si–Cr–N coatings are promising candidates for protective coatings for materials with a poor resistance to oxidation at elevated temperatures. In this article, we examine and present the thermal stability and high temperature oxidation behavior of reactively magnetron sputtered SixCryNz coatings with high content of silicon (> 30 at.%) and N/metal ratios of 0.48 and 1.1. These coatings are investigated under isothermal and dynamic conditions using differential scanning calorimetry and thermal gravimetric analysis for temperatures of up to 1400 °C. The structure and morphology of the oxidized coatings are studied by X-ray diffraction, and electron microscopy. As-deposited SixCryNz coatings represent a composite system consisting of two chemically separated amorphous phases: a-SiNx phase and a-SiCrN phase. The decomposition process connected with N2 release occurs in SixCryNz coatings at an annealing temperature Ta ≥ 1000 °C in an Ar atmosphere and involves a formation of nanocrystalline hcp-Cr2N, Cr5Si3, hcp-Si3N4 and hcp-CrSi2 phases. These structural changes are reflected in an increase in hardness from 13.2 GPa and 19.3 GPa to 34 GPa and 25.6 GPa for Si0.66Cr0.34N0.48 and Si0.66Cr0.34N1.1 coatings, respectively. SixCryNz coatings exhibit considerable oxidation resistance due to the formation of stable and dense Cr2O3 scales. The rapid oxidation of SixCryNz coatings starts as temperature Ta reaches ~ 1090 °C. The dense oxide scale of ~ 0.4 μm is formed during isothermal oxidation of Si0.66Cr0.34N1.1 coatings at the temperature of 1100 °C for 48 h.