A SiO2–Al2O3 glass composite coating was prepared on Ti60 alloy via air spraying slurry and then a suitable baking process. It was composed of potassium silicate glass, alumina and quartz powders. The high temperature oxidation performance of the alloy with and without coating was evaluated in static air at both 800 °C and 900 °C. The results show that catastrophic oxidation occurs for Ti60 bare alloy. It had a mass gain of about 2 mg/cm2 after oxidation at 800 °C and 17 mg/cm2 at 900 °C for 100 h. On the contrary, the oxidation resistance of alloy coated with composite coating was much improved with the mass gain about 0.36 mg/cm2 and 0.95 mg/cm2 at 800 °C and at 900 °C, respectively. The microstructure evolution of the composite coating and the alloy was analyzed by scanning electron microscope and electron probe microanalyzer. The effect of the composite coating on the oxidation performance of the alloy is discussed especially in terms of oxygen diffusion and interfacial reaction.
To clarify the mechanism of the third-element effect in sulphur-containing and sulphur-free oxidation environments, the corrosion behaviours of four kinds of Fe-xCr-ySi (x = 5, 10 at.% and y = 5, 10 at.%) alloys were studied at 600 °C in a H2-CO2 and a H2-CO2-H2S gaseous mixture with the same oxygen partial pressure. The results showed that, in the pure oxidizing atmosphere, thin and slowly growing protective oxide layers were formed on the alloys surfaces. Conversely, all alloys formed a corrosion product layer with an outer layer of FeS and an inner layer of a mix of oxides and sulphides in the oxidizing-sulphidizing atmosphere, which meant that adding Cr into the alloy as the third element had less of an effect on improving the alloy in the harsh sulphidizing-oxidizing environment. The oxidation and sulphidation mechanism as well as the effects of chromium and silicon on the corrosion resistance of the alloys was discussed.
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