Influence of high-temperature pre-treatment on CMAS corrosion resistance of YSZ thermal barrier coatings modified with multiple rare-earth oxides

The objective of this work is to investigate the effects of pre-exposure on the CMAS corrosion behavior of doped and modified Gd2O3-Yb2O3-Y2O3（GYb-YSZ） thermal barrier coatings. Three types of test，such as high-temperature pre-exposure test，CMAS corrosion test，and CMAS corrosion test after high-temperature pre-exposure，are conducted by preparing standard specimens. The changes in microstructure and basic mechanical properties of the coatings after these types of test are comparatively studied using scanning electron microscopy（SEM） and nano indentation，thereby discussing the impact of pre-exposure on CMAS corrosion. The results show that short-term pre-exposure treatment leads to multi-channel penetration，while long-term pre-exposure treatment results in the occurrence of longitudinal through-cracks. Pre-exposure to 980 ℃ or 1050 ℃ for 125 h reduces the penetration effect of CMAS. When the temperature reaches 1150 ℃，CMAS penetrates the top coat in the molten state. In the process of cooling，CMAS re-solidification causes to form vertical cracks resulting from the expansion of columnar grain boundaries，extending through the top coat，and accelerating the spallation of the coating. Meanwhile，after CMAS corrosion，the coating shows a significant increase in Young’s modulus of 48% and hardness of 50% compared to the original sample. Thus，the specimens exhibit significant resistance to CMAS corrosion under pre-exposure treatment at 980 ℃ or 1050 ℃ for 125 h.