Effect of the gas mixture composition on high-temperature behavior of magnetron sputtered Si–B–C–N coatings

The effect of the gas mixture composition on the high-temperature behavior of amorphous Si–B–C–N coatings was systematically investigated up to 1700 °C in a flowing air and inert gases (He and Ar). The Si–B–C–N coatings were deposited by reactive dc magnetron co-sputtering using a single B4C–Si target in two nitrogen–argon gas mixtures (50% N2 + 50% Ar or 25% N2 + 75% Ar). A fixed 75% Si fraction in the target erosion area, an rf induced negative substrate bias voltage of − 100 V, a substrate temperature of 350 °C and a total pressure of 0.5 Pa were held constant in depositions. The high-temperature behavior of the coatings, including their oxidation resistance in air and thermal stability in inert gases, was characterized by means of high-resolution thermogravimetry, differential scanning calorimetry, X-ray diffraction, Rutherford backscattering spectrometry and elastic recoil detection analysis. It was found that the Ar fraction in the gas mixture determines an important N / (Si + B + C) concentration ratio in the coatings, and hence their high-temperature behavior. The coating prepared with a 50% Ar fraction exhibits extremely high oxidation resistance (Δm = 0) up to 1400 °C and very high oxidation resistance (Δm < 0.02 mg/cm2) up to 1600 °C in air, and extremely high thermal stability up to 1600 °C in inert gases. The stability of the coating prepared with a 75% Ar fraction is very high up to the onset (at about 1250 °C) of crystallization of its initial amorphous structure.