Novel double ceramic coatings based on Yb2Si2O7/La2(Zr0.7Ce0.3)2O7 by plasma spraying on Cf/SiC composites and their thermal shock behavior

Yb2Si2O7 and La2(Zr0.7Ce0.3)2O7 (or LZ7C3) ceramic powders have been synthesized by solid-state reaction using constituent oxide powders as starting materials in appropriate molar ratios. The fabricated powders were subjected to spray drying treatment for subsequent syntheses of coatings. Double ceramic layer coatings based on Yb2Si2O7 as interlayer and La2(Zr0.7Ce0.3)2O7 as the top coat are synthesized on Cf/SiC composite coupons by air plasma spraying (APS). Coatings are subjected to thermal shock testing between 400 °C and 1500 °C in a gas burner rig experiment. X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and thermogravimetry with differential scanning calorimetry (TG/DSC) were performed on the processed products. Our studies show that the LZ7C3 powders after undergoing through the plasma flame result in the formation of coating dominant in pyrochlore structure. Bulk part of the LZ7C3 based coatings was found intact with the substrate on thermal shock testing, however, with the presence of cracks in the surface and its partial transformation into constituent oxides. Meanwhile, evaporative loss of cerium happens on progressed thermal cycling. The chemical nature of interaction across the interface was assessed by heating Yb2Si2O7 and LZ7C3 powders and carrying out the XRD. At 1275 °C for 24 h, almost no reactions took place. However, on heating at 1475 °C for 24 h, microchemistry of the resulted powder is also characterized by the presence of decomposed phases of LZ7C3 and the reaction products, especially the cerium based di-silicate.