Dual-phase barrier formation and inhibition of environmental deposit-induced grain boundary corrosion in rare earth zirconia-based TBCs

Thermal barrier coatings (TBCs) are subjected to severe corrosive attack from environmental deposits (dust, sand, volcanic ash, etc.) during high-temperature service, resulting in significant degradation of coating performance and eventual structural failure. However, the corrosion mechanisms of TBCs under attack from impurity-rich, low Ca: Si environmental deposits (CMAS-E) remain poorly understood. This study systematically compares the corrosion behavior of yttria-stabilized zirconia (YSZ), multi-rare-earth-stabilized zirconia (RSZ), and gadolinium zirconate (GZO) coatings exposed to CMAS-E at 1300 °C. Both YSZ and RSZ coatings fail via a grain-boundary-dominated mechanism, where melt infiltrates along coating defects to form discontinuous zircon products. This failure to form a protective barrier leads to deep melt penetration and severe stress-induced bending. By comparison, the GZO coating exhibits enhanced resistance by forming a continuous, dense dual-phase barrier of apatite and Gd-enriched fluorite phase through a uniform surface reaction. This distinctive “self-sacrificial” mechanism is driven by the large optical basicity difference between GZO and the acidic CMAS-E melt, coupled with a high Gd 3+ content. This work provides fundamental insights for designing TBCs with enhanced environmental durability through controlled interfacial reactions. • GZO vastly outperforms YSZ/RSZ against low Ca:Si, impurity- containing CMAS-E attack. • YSZ/RSZ fail via grain boundary attack, forming discontinuous zircon precipitates. • GZO forms a dense, dual-phase barrier of apatite and GdSZ via uniform reaction. • High optical basicity of GZO drives interfacial reaction, halting melt infiltration.