Using Ti-Al-Zr target and pure Cr target, the multi-component nitride films, (Ti, Al, Zr, Cr) N, were deposited on the substrates of high speed steel (W18Cr4V) by multi-arc ion plating technique. The high temperature oxidation of the film was carried out in the case of both the short-time (600 ℃, 700 ℃, 800 ℃ and 900 ℃ for 4 h) and long-time (700 ℃ and 800 ℃ for 100 h) tests. All of the specimens were characterized by scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS) and X-ray diffraction (XRD). It was shown that the high temperature oxidation resistance of the film was up to 800 ℃ in case of short-time oxidation, and TiO₂ formed on the (Ti, Al, Zr, Cr) N film; while oxidation resistance of the film was up to 700 ℃\linebreak in case of long-time oxidation.

ΔG⁰-T diagrams of the reactions between some typical transition metal carbides (or borides) and oxygen were drawn using Matlab software. On the basis of these ΔG⁰-T diagrams, equilibrium partial oxygen pressures were obtained accordingly. The volatility diagrams for ZrC-ZrO₂ system and SiC-SiO₂ system at \linebreak2500 K were drawn and the function of the partial press of various related products in the ZrC-ZrO₂ system with temperature was evaluated. The calculation results indicated that the oxygen activity and equilibrium partial oxygen pressure of these carbides changed with temperature. According to the volatility diagrams of ZrC-ZrO₂ and SiC-SiO₂ systems, the vapour pressure of related oxides may be very high at the interfaces, even higher than 10⁵ Pa, which is detrimental to the formation of entire oxide scales on carbides during ultra-high temperature oxidation. This work provided significant insight into the behaviour of ultra-high temperature oxidation of C/C composites and ultra-high temperature ceramics. It especially provided theoretical considerations for choosing oxidation-resistance dopants in C or C/C composites.

Cr_0.82Al_0.18N and Cr_0.53Al_0.47N coatings were deposited on a Ti₃Al based alloy by reactive magnetron sputtering method. Hot corrosion of these two coatings in 75 mass % Na₂SO₄+25 mass % K₂SO₄ molten salt at 800 ℃ was performed in a Setsys 16/18 thermoanalyzer. The phase compositions of the corrosion products were identified by X-ray diffractometer (XRD). Both the surface and cross-sectional morphologies of the samples were observed by a scanning electron microscope (SEM). The results showed that both Cr_0.82Al_0.18N and Cr_0.53Al_0.47N can reduce the hot corrosion rate of the Ti₃Al based alloy and their hot corrosion resistance decreases with increasing aluminum content; the main corrosion products of the coatings are Cr₂O₃ and θ-Al₂O₃ and the amount of θ-Al₂O₃ in the corrosion products is proportional to the Al content in the coating. The better hot corrosion resistance of Cr_0.82Al_0.18N coating can attribute to the high stability of Cr₂O₃ in the molten salt.