Microstructure and phase composition evolution of dual-phase ytterbium silicate coatings plasma sprayed from stoichiometric Yb2Si2O7 feedstock powder

The main challenges of atmospheric plasma spraying (APS) when dealing with rare earth silicate are the amorphous phase formation and silica volatilization in as-sprayed coatings. In this study, the microstructure and phase composition evolution of dual-phase ytterbium silicate environmental barrier coatings (EBCs) plasma sprayed from stoichiometric Yb2Si2O7 feedstock powder are investigated. The unavoidable silica volatilization leads to the coating composition deviate from stoichiometry of disilicate composition and result in the presence of Yb2SiO5 in coatings. By controlling the phase fraction of Yb2SiO5 through modulation of plasma character allows minimizing the effects of thermal residual stress on the coating durability in thermal cycling. The high crystallinity and crack-free coatings were achieved through optimized crystallization heat treatment. The presence of dislocation and deformation twins endow the dual-phase coating with intrinsic quasi plasticity and improvement in reliability. The present study provides useful inspirations on the optimization of spraying parameters and design of advanced EBC systems.