Composition and oxidation resistance of Ti–B–C and Ti–B–C–N coatings deposited by magnetron sputtering

Nanocomposite Ti–B–C and Ti–B–C–N coatings were deposited from a TiB2–TiC target using RF magnetron sputtering. In this paper, the composition and oxidation kinetics of Ti–B–C and Ti–B–C–N coatings are presented. The film composition was characterized using XPS. Compared to the target composition, preferential sputtering of the carbon component was observed. Introducing nitrogen into the sputtering gas resulted in the formation of TiN, with nitrogen of approximately 30 at.%, and shifted the C1s peak from the typical position for carbide to a higher binding energy position, which is typical of graphite. Both dynamic and isothermal oxidation kinetics were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The oxide compositional depth profile, structure and morphology were characterized by Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results show that: (1) catastrophic oxidation started at 920 K; (2) TiB2 and TiC in Ti–B–C coatings oxidized in sequence; (3) isothermal oxidation of Ti–B–C coatings in the temperature range from 1173 to 1323 K obeyed a parabolic rate law with an activation energy of 1.64 eV/atom, indicating a diffusion-controlled mechanism; and (4) well-crystallized oxide scales formed after oxidation in air at 1173 K for 2 h are mainly rutile TiO2, with XRD-detectable hexagonal B2O3 and hematite Fe2O3 resulting from iron outward diffusion.