# Unveiling the Corrosion Mechanisms of High‐Entropy RETaO4 Through In Situ Observation

## TL;DR

This study reveals how different rare-earth compositions affect the corrosion resistance of RETaO4, identifying the best-performing material for thermal barrier coatings.

## Contribution

The study introduces a reaction-diffusion mechanism for CMAS corrosion in RETaO4 and identifies an optimal composition with superior corrosion resistance.

## Key findings

- In situ analysis reveals dynamic crystallization pathways of the pyrochlore corrosion product in RETaO4.
- La1/6Nd1/6Sm1/6Eu1/6Gd1/6Dy1/6TaO4 shows the best corrosion resistance with minimal layer thickness and no element segregation.
- A reaction-diffusion mechanism explains the varying behaviors of rare earth elements during CMAS corrosion.

## Abstract

The ambiguous understanding of calcium‐magnesium aluminosilicate (CMAS) corrosion mechanisms in RETaO4 has hindered performance optimization through rare‐earth compositional engineering. This study systematically investigates the corrosion behavior of 3–10 component RETaO4 systems. In situ X‐ray diffraction/Transmission electron microscope coupled with Electron backscatter diffraction analysis unveils dynamic reaction pathways during the pre‐corrosion heating stage, identifying the crystallization and growth patterns of dominant corrosion product pyrochlore‐structured (Ca2‐a‐bREaAlb)(Ta2‐c‐dMgcSid)O7. A reaction‐diffusion mechanism of CMAS corrosion for RETaO4 is proposed, highlighting the different behaviors of various rare earth elements in the corrosion process. Among eight types of RETaO4, La1/6Nd1/6Sm1/6Eu1/6Gd1/6Dy1/6TaO4 exhibits the best corrosion resistance, with a relatively thin corrosion layer and the ability to avoid element segregation and localized infiltration. These findings establish composition‐property relationships for designing next‐generation corrosion‐resistant thermal barrier coatings.

Composition‐property relationships in multi‐component RETaO4 are unveiled. In situ XRD/TEM and EBSD expose dynamic crystallization pathways of the dominant corrosion product (pyrochlore) and reaction‐diffusion corrosion mechanisms. La1/6Nd1/6Sm1/6Eu1/6Gd1/6Dy1/6TaO4 emerges as the optimal composition, combining minimal corrosion layer thickness with suppressed localized infiltration.