Progress in ceramic materials and structure design toward advanced thermal barrier coatings

Abstract

Thermal barrier coatings (TBCs) can effectively protect the alloy substrate of hot components in aeroengines or land-based gas turbines by the thermal insulation and corrosion/erosion resistance of the ceramic top coat. However, the continuous pursuit of a higher operating temperature leads to degradation, delamination, and premature failure of the top coat. Both new ceramic materials and new coating structures must be developed to meet the demand for future advanced TBC systems. In this paper, the latest progress of some new ceramic materials is first reviewed. Then, a comprehensive spalling mechanism of the ceramic top coat is summarized to understand the dependence of lifetime on various factors such as oxidation scale growth, ceramic sintering, erosion, and calcium-magnesium-aluminium-silicate (CMAS) molten salt corrosion. Finally, new structural design methods for high-performance TBCs are discussed from the perspectives of lamellar, columnar, and nanostructure inclusions. The latest developments of ceramic top coat will be presented in terms of material selection, structural design, and failure mechanism, and the comprehensive guidance will be provided for the development of next-generation advanced TBCs with higher temperature resistance, better thermal insulation, and longer lifetime.

Mechanical property enhancements and amorphous thermal transports of ordered weberite-type RE3Nb/TaO7high-entropy oxides

“…The variation in the TECs of YTaO 4 before and after the phase transition temperature is negligible, which is vital for its application in TBCs. Good high-temperature phase stability is essential for TBCs [5], environmental barrier coatings (EBCs) [56,57], and abradable seal coatings [58] in aeroengines. The prepared HEOs exhibit better hightemperature phase stability and higher working temperatures than 7YSZ, indicating their extensive application prospects.…”

“…However, weberite-type RE 3 Nb/TaO 7 ceramics had inadequate mechanical properties, e.g., La 3 NbO 7 had hardness, toughness, and Young's modulus of approximately 4.5 GPa, 0.5 MPa•m 1/2 , and 100 GPa, respectively [23]. 7 yttria-stabilized zirconia (7YSZ), La 2 Zr 2 O 7 , and Yb 3 NbO 7 had high hardness (H = 913 GPa) and Young's modulus (E = 200250 GPa), and 7YSZ were widely used as protective coating materials due to their excellent fracture toughness (K IC = 3.5 MPa•m 1/2 ) [2,5,15,16,19]. The fluorite RE 3 Nb/TaO 7 HEOs have been studied to optimize their properties.…”

“…The lower the density, the smaller the centrifugal force, and it contributes to prolonging lifetime of TBCs. The other is that LaGd elements with large ionic radii will rapidly react with CaOMgOAlO 1.5 SiO 2 (CMAS) at high temperatures to form stable reactants with large unit cell volumes and inhibit further CMAS corrosion [5,17,19]. It is believed that weberite-type RE 3 Nb/TaO 7 ceramics exhibit better CMAS corrosion resistance than fluorite-type competitors.…”

Adhesion in thermally sprayed coatings: An insight from interfacial residual stress

“…The residual stress at the rough coating-substrate interface perpendicular to the interface influences the crack propagation and, hence, coating adhesion. 17,18 A tensile residual stress is generated at the hills region, whereas the valley regions harbor a compressive residual stress in an as-sprayed thermal barrier coating as investigated by Chang et al 19 and Hsueh et al 20 through numerical simulation. Hence, cracks are expected to grow from the hill location and propagate to the valley region.…”

“…The roughness of the grit‐blasted substrate and as‐sprayed bondcoat has an influence on the in‐plane residual stress state. The residual stress at the rough coating–substrate interface perpendicular to the interface influences the crack propagation and, hence, coating adhesion 17,18 . A tensile residual stress is generated at the hills region, whereas the valley regions harbor a compressive residual stress in an as‐sprayed thermal barrier coating as investigated by Chang et al 19 .…”