The failure of premature thermal cycling spalling off is the bottleneck problem currently faced by yttrium oxide partially stabilized zirconia (YSZ) ceramic-based sealing coatings. Studies on the thermal cycling performance of coatings with “brick-mud” structures were carried out by experimental and simulation methods in this paper. The results showed that, as the thickness of “mud” layer increased, the bonding strength of the “brick-mud” structure coatings gradually decreased. When the thickness of the “mud” layer was about 3 μm and 10 μm, the thermal cycling lives of the T1 and T2 coatings were improved by 90.0% and 135.7%, respectively, compared with conventional coating (T0 coating), while that of the T3 coating (containing thick “mud” layers of about 20 μm) was decreased by 81.4%. The stress field of M2 “mud” layers with different thicknesses was subjected to a comprehensive effect by thermal mismatch stress and pores in “brick” layer. Compared with the medium and thick “mud” layers, the thin “mud” layer sustained obvious larger ${\sigma }_{22 max}$ and ${\sigma }_{12 max}$, indicating its potential for the preferential initiation of transverse microcracks. In addition, the thin “mud” layer withstood the largest ${\sigma }_{11 max}$ and had the strongest potential for longitudinal crack growth. Both transverse and longitudinal cracking could consume energy during thermal cycling and reduce the stress concentration at the top coating/bond coating interface. These were the main reasons for the improvements in the thermal cycling performances of the T1 and T2 coatings. The degree of crack deflection and the capacity of energy dissipation in the “mud” layer increased significantly with its thickness. However, the propagation length of transverse cracks also gradually increased in the meantime. Especially when the “mud” layer was 20 μm, the length of the transverse cracks increased rapidly. Thus, early interlayer delamination failure occurred in the T3 coating during thermal cycling.

Ceramic thermal protective coatings during long-term service in high-temperature environments are prone to micropore shrinkage, grain coarsening, and porous structure collapse, leading to severe densification. This consequently degrades the durability and reliability of the ceramic coatings. This paper elucidates the sintering densification mechanism of ceramic coatings, analyzes innovations in material systems and multidimensional structural design strategies, and summarizes the state-of-the-art research progress on anti-sintering densification of ceramic coatings. The limitations of conventional techniques that inhibit high-temperature sintering densification via “passive pore retention” are highlighted. A novel strategy based on phase transformation-induced pore formation for achieving “active in situ pore generation” is explored. On this basis, future research directions for enhancing the anti-sintering densification performance of ceramic thermal protective coatings are proposed.

To address the softening and limited oxidation and water-vapor corrosion resistance of Si bond coats at ultra-high temperatures, Si and Si–15 mol% HfO₂ (denoted 15HS) composite bond coats were deposited on pressureless sintered SiC substrates by air plasma spraying (APS). Their phase evolution, cross-sectional microstructure, and failure mechanisms were examined after 20–200 h at 1623 K in dry oxygen and in a 90% H₂O–10% O₂ environment. In dry oxygen, a SiO₂ thermally grown oxide (TGO) layer formed on the Si coating surface, cracked and spalled with time, and the coating thinned progressively. In the 15HS coating, HfO₂ reacted in situ with SiO₂ to form HfSiO₄; the combined volume expansion and spallation resistance of the dense layer caused the coating to thicken rather than thinning, and the TGO remained dense and crack-free. Under water-vapor corrosion, the Si coating was continuously consumed through gas-phase volatilization of SiO₂ as Si(OH)₄, accompanied by porosity and through-thickness cracks; after 200 h the coating thickness was only ~70% of the initial value. The 15HS coating instead underwent a three-stage evolution—homogeneous oxidation, layered construction, and barrier stabilization—after which a dense double-layer barrier formed, with an outer HfSiO₄ layer and an inner SiO₂ band, giving a thickness retention of ~90%, well above that of the Si coating. Mechanistic analysis showed that HfO₂ particles remained in place while Si⁴⁺ diffused outward and converted to HfSiO₄ at the HfO₂ surface. HfSiO₄ protected the coating through two mechanisms: blocking OH⁻/H₂O diffusion pathways and suppressing Si(OH)₄ volatilization. These findings inform the compositional optimization and structural design of Si-based bond coats for ultra-high-temperature water-vapor service.

Ceramic thermal protective coatings subjected to long-term service in high-temperature environments are prone to internal micro-pore shrinkage, grain coarsening, and collapse of the porous structure, forming a compacted structure. This consequently degrades the durability and safety of the ceramic coatings. This paper elucidated the sintering densification mechanism of ceramic coatings. It analyzed both innovations in material systems and multi-dimensional structural optimization of coatings, summarizing domestic and international research progress on the sintering densification resistance of ceramic coatings. The limitations of traditional techniques that inhibit high-temperature sintering densification through “passive pore retention” were highlighted. A novel approach based on phase transformation-induced pore formation to achieve “active in-situ pore generation” was explored. Building on this, future research directions for enhancing the sintering densification resistance of ceramic thermal barrier coatings were proposed.

As turbine inlet temperatures increase, the long-term stability of conventional yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) becomes difficult to maintain. Molten calcium–magnesium–alumino-silicate (CMAS) rapidly infiltrates atmospheric plasma-sprayed (APS) coatings through interconnected pores and cracks. In this work, an AlCl₃-derived precursor sol prepared from AlCl₃·6H₂O in a deionized water–ethanol mixture (1:1, v/v) was introduced into the defects of high-entropy rare-earth zirconate (HE-REZ) coatings by vacuum-assisted drop-casting and subsequently converted into Al₂O₃ in situ through heat treatment. The influence of this treatment on the microstructure, surface wettability, and CMAS corrosion resistance of the coatings was examined. The newly formed Al₂O₃ was present on the coating surface and within pores and microcracks, where it narrowed or sealed the infiltration paths. After modification, surface roughness decreased by 8.96%, and the mean apparent contact angle measured on cooled CMAS/coating cross-sections increased by approximately 28°. Defect filling reduced the effective size of the infiltration channels, while dissolution of Al₂O₃ into the melt increased its viscosity and slowed capillary infiltration. Filling retained the dominant corrosion mechanism but shifted CMAS attack from rapid, localized penetration to a more uniform advance of the reaction front, reducing the corrosion rate and structural damage. Alumina filling therefore improves the CMAS corrosion resistance of APS HE-REZ TBCs by restricting infiltration channels and increasing melt viscosity.

The advancement of aerospace technology has driven a trend towards aeroengines with higher thrust-to-weight ratios and elevated service temperatures. Hot-section components such as combustion chamb...