Influence of phase composition on thermal aging behavior of plasma sprayed ytterbium silicate coatings

In this study, ytterbium silicate coatings with different phase compositions were designed by controlling Yb2O3/SiO2 ratio and fabricated by atmospheric plasma spray (APS) technique. Thermal aging behaviors such as microstructure evolution and thermomechanical properties were focused, and the influence of phase composition was analyzed. Results showed that obvious grain growth and defect reduction occurred, and the thermomechanical properties were significantly modified after thermal aging. The larger reduction in defects and greater increase in elastic modulus, Vickers hardness and coefficient of thermal expansion took place in the Yb2O3-rich coatings containing Yb2O3 and Yb2SiO5 phases. The bigger grains and transgranular cracks were formed and the greater increase in thermal conductivity took place in the SiO2-rich coatings containing Yb2SiO5 and Yb2Si2O7 phases. The relationship among microstructure evolution and variation of thermomechanical properties was analyzed. The results of this study may provide a reference for design and application of rare-earth silicates as environmental barrier coatings (EBCs).