Effect of deposition temperature on phase composition, morphology and mechanical properties of plasma-sprayed Yb2Si2O7 coating

Abstract Phase composition, microstructure and mechanical properties of ytterbium disilicate (Yb2Si2O7, YbDS) coatings fabricated via atmospheric plasma spray (APS) at different deposition temperatures were studied. Two layers with distinct pore distributions were observed in the YbDS top coat, the formation of pores correlated fairly well with the thermal gradients of splats after the droplets impinged on the substrate or deposited splats. Microstructure evolution with the thicknesses of YbDS top coat resulted from splat stacking and temperature accumulation. In addition, the significant crystallinity improvement and cracks reduction of YbDS top coat arose with the increased deposition temperature. X-ray diffraction patterns indicated that the metastable ytterbium monosilicate (Yb2SiO5, YbMS) appeared in YbDS coatings and they disappeared after thermal-treatment due to the phase transformation. The mechanical properties of the YbDS coatings were affected notably by the phase composition and microstructure.