Tunable properties of (HoxY1-x)2SiO5 as damage self-monitoring environmental/thermal barrier coating candidates

RE2SiO5 with low thermal conductivity, compatible thermal expansion coefficients and excellent high-temperature reliability in harsh environments are excellent candidates as advanced environmental/thermal barrier coating materials for high-efficiency gas turbine engines. A series of rare earth silicates (HoxY1-x)2SiO5 are designed and their properties are comprehensively investigated in this paper. Through doping Ho into Y2SiO5, the thermal conductivity of Y2SiO5 is significantly decreased and the thermal expansion coefficient is also optimized closer to Si-based ceramics. High-temperature elastic stiffness and bending strength are increased with the enhancing of Ho content. Most important, doping Ho element provides (HoxY1-x)2SiO5 with tunable luminescence characteristic. (HoxY1-x)2SiO5 exhibit green, to yellow-green, then to orange-red luminescence color with increased Ho concentration. The results show that they can be used as damage self-monitoring environmental/thermal barrier coating materials for Si-based ceramics.