Investigating CMAS corrosion in ultrahigh temperature Hf₆Ta₂O₁₇-based thermal barrier coatings: A mechanism by which corrosion products hinder corrosion resistance

Abstract

Hf₆Ta₂O₁₇ ceramic has outstanding thermal and mechanical properties, along with an extremely high phase transition temperature (2517 K), making it a promising candidate for next-generation thermal barrier coatings (TBCs). High-temperature corrosion of TBCs by calcium-magnesium-alumino-silicates (CMAS) is a major failure mode. To understand why Hf₆Ta₂O₁₇ ceramic resists CMAS corrosion well at high temperatures, the CMAS/Hf₆Ta₂O₁₇(010) system was analyzed via density functional theory to study CMAS – induced corrosion processes. Results show that above 1523 K, the diffusion coefficient of atoms in CMAS exceeds that in Hf₆Ta₂O₁₇(010). Also, there is significant mutual diffusion between (Ca, Si) and (Hf, Ta) with a low diffusion activation energy. The interaction between CMAS and Hf₆Ta₂O₁₇ has a low reaction energy, enabling the quick formation of dense corrosion products (CaTa₂O₆ and HfSiO₄) at the interface. These products have high phase stability and fast formation rates, remaining intact when in contact with residual CMAS. The interface-formed corrosion products greatly reduce the CMAS diffusion coefficient into Hf₆Ta₂O₁₇; for instance, calcium, the fastest-diffusing element, has its diffusion coefficient reduced by over five times. These mechanisms effectively limit CMAS corrosion of Hf₆Ta₂O₁₇, enhancing its potential as an ultrahigh temperature TBCs for the next generation.

Keywords

CMAS corrosion mechanism / diffusion dynamics / first-principles calculation / Hf₆Ta₂O₁₇ / thermal barrier coatings

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2025 The Author(s). Materials Genome Engineering Advances published by Wiley-VCH GmbH on behalf of University of Science and Technology Beijing.