A4Ta2O9 (A=Ca, Mg) tantalate as novel thermal barrier coatings materials with superior calcium-magnesium-alumino-silicate corrosion resistance

Abstract

The CaO-MgO-AlO1.5-SiO2 (CMAS) corrosion leads to premature failure of thermal barrier coatings (TBCs), which has beset scholars for decades. Previous study has shown that A4Ta2O9 (A=Ca, Mg) tantalates are promising TBCs attributed to the excellent thermo-mechanical properties, and this work elucidates the robust CMAS corrosion resistance of A4Ta2O9 from CMAS contact angle, reaction products, corrosion depth, thermal stress, and reaction activity. It is found out that the main reaction products between CMAS and A4Ta2O9 are Ca2Ta2O7, and the abundant Ca2+ ions in Ca4Ta2O9 can promote formations of a dense Ca2Ta2O7 reaction layer, which can prevent further penetrations of CMAS melts. Additionally, a small CMAS contact angle and higher optical basicity differences between Ca4Ta2O9 and CMAS prove that their reactions are more intense than those between Mg4Ta2O9 and CMAS, which are beneficial for accelerating the formations of a dense Ca2Ta2O7 reaction layer. The interface thermal stress between A4Ta2O9 and Ca2Ta2O7 reaction layer is estimated based on nano Young’s modulus, and Mg4Ta2O9 has higher thermal stress than Ca4Ta2O9 because it has a higher modulus. The lower of interface thermal stress, the better of high-temperature stability. Accordingly, Ca4Ta2O9 is proposed as a novel CMAS-resistant TBC material.