Preparation and phase structure optimization of plasma-sprayed Yb2SiO5 environmental barrier coating

Rare earth ytterbium monosilicate (Yb2SiO5) is one of the most ideal candidates for environmental barrier coatings. In this paper, Yb2SiO5 coating was successfully fabricated by atmospheric plasma spraying technology. The effect of main gas flow rate and spraying powder composition on the microstructure and phase composition of Yb2SiO5 coating were systematically investigated to solve the volatilization of SiO2 during plasma-spraying process. The results showed that Yb2SiO5 coating was relatively dense with the less internal defects under the main gas flow rate of 35 L/min, and the main gas flow rate from 30 L/min to 40 L/min had no significant effect on the melting effect of spraying powder and the porosity of coating. Yb2SiO5 coating was composed of Yb2O3, Yb2SiO5 two crystal phases and amorphous phase. The phase composition of coating was not affected by the change of main gas flow rate. After heat-treatment at 1400 degrees C for 20 h, Yb2SiO5 crystal phase precipitated from the coating, and the content of Yb2SiO5 phase reached 74.29 mol%, and the remaining phase was Yb2O3 phase. The Yb2SiO5-25.71 mol% SiO2 coating was still dense, the content of Yb2SiO5 crystal phase was up to 97.76 mol % after heat-treatment, and the content of Yb2Si2O7 phase was only 2.24 mol%, indicating that excessive addition of a certain amount of SiO2 could compensate for the volatilization of SiO2, so as to prepare Yb2SiO5 coating with approximate stoichiometric ratio.