Development of Silicates and Spraying Techniques for Environmental Barrier Coatings

Currently, silicon carbide fibre-reinforced silicon carbide matrix ceramic matrix composites are widely used as high-temperature components for next-generation gas-turbine engines. However, hot steam and volcanic ash degrade the mechanical properties of silicon carbide. Environmental barrier coatings (EBCs) play an important role in mitigating corrosion under the harsh operating conditions required for next-generation turbines. In addition to corrosion resistance, the coefficient of thermal expansion and phase stability are important for EBC material selection to stabilise the layer structure during thermal cycling. Various silicates have been considered as candidates for EBCs, where rare-earth silicates have shown promising results. Moreover, various spraying techniques that can achieve a layered EBC structure have been considered in addition to appropriate material selection as key strategies for improving the reliability and lifetime of EBCs. Crystallisation, porosity, and crack formation caused by the formation of secondary phases due to Si evaporation are controlled by thermal spraying techniques. This chapter comprehensively evaluates the selection of silicates and spraying techniques for EBCs and discusses their prospects.