Microstructure and oxidation resistant behavior of Er2Si2O7 and Er2Si2O7/LaMgAl11O19 coatings deposited on Cf/SiC composites by APS at 1723Â K

Er2Si2O7 and Er2Si2O7/LaMgAl11O19 coatings were fabricated on Cf/SiC composites by atmospheric plasma spraying (APS) in order to improve the oxidation resistance of the substrate. Microstructure and oxidation resistant behavior of the coatings were investigated at 1723 K in the thermal shock furnace. The results showed that the as-sprayed coatings were uniformly distributed on the substrate and bonded well with the substrate. The bared substrate has the maximum weight loss of 43.8% after 8 thermal shock cycles with the total heating time of 120 min, while for the samples coated with the Er2Si2O7 and Er2Si2O7/LaMgAl11O19 coatings, the weight losses were only up to 3.73% and 1.88%, respectively. Due to the difference of coefficients of thermal expansion between coatings and substrate, the sintering of Er2Si2O7 layer, the surface oxidation of substrate and the interfacial reactions between the ceramic layers, the through cracks and horizontal cracks appeared in the coatings with the thermal shock cycle increasing, which significantly led to the increasing weight loss for the coated samples. The oxidation protection of Er2Si2O7 and Er2Si2O7/LaMgAl11O19 coatings for Cf/SiC composites at 1723 K is much attractive for the short-term application such as several thermal shock cycles with the total heating time of tens of minutes.