Microstructure and properties characterisation of the double layered glass–ceramic coating on near-α titanium alloy

A protective double layered glass–ceramic coating was produced by slurry technique in order to improve the oxidation resistance of Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si-0.06C-0.09O, wt.%, at temperatures above 600 °C. A SiO2–P2O5–B2O3–CaO–K2O–Na2O layer was produced as the outer layer, with self-healing properties. Analytical scanning- and transmission electron microscopy were used for detailed analyses of the microstructure and phase composition of the coating. It was found that both layers contain several crystalline and amorphous phases. It was established that the double layered glass–ceramic coating formed on TIMETAL 834 shows higher hardness than the substrate alloy and better oxidation resistance at elevated temperature, since no weight change of the coated alloy was observed after oxidation for 300 h at 800 °C. The self-healing behaviour of the outer layer was also demonstrated.