3.2.1 enamel and glass ceramic coating
Wang Fuhui and Zhu Shenglong developed enamel coatings for superalloys and titanium alloys. Enamel is to burn one or more layers of non-metallic inorganic materials on the metal surface. In high temperature enamel, the metal and inorganic materials have appropriate physical and chemical reactions at high temperature, forming chemical bonds at the interface, so that the coating and the base material can be firmly combined into a whole. The thermal expansion coefficient of enamel coating is adjustable, and it has high thermochemical stability, compact structure and excellent corrosion resistance. At the same time, the preparation process of the coating is simple and the cost is low. As an inert high-temperature corrosion resistant coating, it has no problems such as the consumption of oxidation resistance components of the traditional high-temperature coating. Therefore, as a long-life corrosion resistant coating, it has a good application prospect. In view of the brittleness of the enamel itself, Chen Minghui and others added NiCrAlY metal powder to the enamel to modify it, and prepared a new type of metal composite enamel with excellent thermal shock resistance, and studied its toughening mechanism in depth.

Das et al., Datta et al. And Sarkar et al. Have prepared mgo-al2o3-tio2, zno-al2o3-sio2 and bao-mgo-sio2 high temperature resistant glass ceramic coating. This coating is also prepared by high temperature enameling method, which is suitable for nickel based superalloy parts of gas turbine and protection of γ - TiAl alloy. The coating has excellent oxidation resistance and thermal shock resistance at 1050 ℃ and below. They also tried to prepare the coating by microwave heating.

3.2.2 metal glass composite thermal barrier coating
A new type of metal glass composite thermal barrier coating (MGC) consisting of glass and NiCoCrAlY alloy is proposed in the literature. MGC coating is prepared by vacuum plasma spraying. The thermal expansion coefficient of the coating can be adjusted by the ratio of metal to glass to match the substrate. In addition, the coating is air tight, which can protect the substrate and the bonding layer from corrosive atmosphere. The results of isothermal and cyclic oxidation tests at 1000 ℃ and 1200 ℃ showed that the life of MGC coating was significantly longer than that of traditional YSZ coating.

Glass based coating has the advantages of high thermal stability and good corrosion resistance, but it is easy to soften at high temperature, and its brittleness is large at low temperature. By adjusting and optimizing the composition of the coating, the softening point and toughness of the coating can be improved, so this kind of coating has great potential for application.