Unraveling the composition-dependent CMAS corrosion resistance in A6B2O17 (A = Hf, Zr; B = Ta, Nb) ceramics: An experimental and first-principles study

Despite their promise as candidates for thermal barrier coatings (TBCs), the engineering application of A 6 B 2 O 17 ( A = Hf, Zr; B = Ta, Nb) ceramics is currently limited by a lack of comprehensive understanding regarding their CMAS corrosion behavior and underlying mechanisms. This paper addresses this gap by elucidating the governing effects of compositional modulation and corrosion conditions on the CMAS corrosion performance of these ceramics, integrating experimental and first-principles theoretical approaches. The results demonstrate that while all compositions exhibit similar corrosion products and resistance mechanisms, A 6 Ta 2 O 17 (particularly Hf 6 Ta 2 O 17 ) displays superior corrosion resistance. This enhanced performance is attributed to a combination of factors, including its exceptional thermodynamic stability, reduced Ca 2+ diffusivity, the significant barrier effect of its dense corrosion product layer, and stronger interfacial bonding strength. Corrosion-induced spallation in Zr 6 B 2 O 17 primarily stems from two factors: the phase transformation of ZrO 2 and an inherently weak interfacial bonding strength. Moreover, while an elevated Ca/Si ratio increases the aggressiveness of CMAS melts, the formation of a dense corrosion product layer on the ceramic surface effectively mitigates this detrimental effect.