Response of molten silicate infiltrated Gd2Zr2O7 thermal barrier coatings to temperature gradients

Abstract

The delamination tendency for bilayer gadolinium zirconate/yttria-stabilized zirconia (GZO/YSZ) thermal barrier coatings (TBCs) was investigated using a continuous laser-based thermal gradient test and a computational model for the analysis of multilayer structures. TBCs with different architectures were exposed to molten silicate compositions, representative of aeroengine deposits, and subjected to thermal cycles prescribed to impart specified levels of strain energy in the coating. The exposed surface of the intercolumnar gaps in the outer part of the GZO layer was found to rapidly dissolve into the intruding molten silicate and precipitate reaction products that seal the flow paths, limiting the penetration depth and the ensuing stiffening of the TBC. Nevertheless, the stiffened layer magnifies the thermal stresses in the coating upon thermal cycling. The influence of the thermal history and multilayer structure on the driving force for delamination was modeled and compared with the experimental results. The effects that the substrate coefficient of thermal expansion, the temperature gradient, and the TBC thickness have on the driving force for delamination were analyzed and the critical amount of stored elastic strain energy for failure under different scenarios was assessed.

Equimolar YO1.5 and TaO2.5 co‐doped ZrO2 as a potential CMAS‐resistant material for thermal barrier coatings

“…Actually, for many CMASresistant TBCs materials, like Gd 2 Zr 2 O 7 , the protective dense reaction layer tends to spall during the cooling, due to the huge thermal mismatch stress. 5,23 For the reaction product #2, which forms the dense reaction layer of ZYTO, the stable tetragonal phase means that there is no phase-transformation stress yielded during the cooling stage. On the contrary, the same tetragonal crystal structure of product #2 and ZYTO implies that there is no significant CTE mismatch stress yielded during the cooling.…”

“…However, the application of these materials in TBCs is limited by their low-fracture toughness and/or thermal expansion coefficient. [23][24][25][26] The new CMASresistant TBCs materials should also have comparable (even better) thermal and mechanical properties compared with 7YSZ. 27 In this work, an equimolar YO 1.5 and TaO 2.5 co-doped zirconia (ZYTO) 28 with chemical composition of Zr 0.66 Y 0.17 Ta 0.17 O 2 is proposed as a new CMAS-resistant TBCs material based on the following considerations.…”

The role of ceramic and glass science research in meeting societal challenges: Report from an NSF‐sponsored workshop

“…All known turbine hot section materials, whether metallic or the recently introduced ceramic composites (CMCs), rely on ceramic coatings. However, both the thermal barrier coatings (TBCs) used to protect metallic components and the environmental barrier coatings (EBCs) used to protect CMCs are temperature limited when exposed to molten dusts, which comprise highly corrosive calcium‐magnesium aluminosilicates (CMAS) . A second major barrier is associated with coating toughness limitations, as the consequences of coating loss become more critical with increasing reliance on their continued protection.…”

“…However, both the thermal barrier coatings (TBCs) used to protect metallic components 164,169 and the environmental barrier coatings (EBCs) used to protect CMCs 164,170 are temperature limited when exposed to molten dusts, which comprise highly corrosive calcium-magnesium aluminosilicates (CMAS). 164,[171][172][173][174][175] A second major barrier is associated with coating toughness limitations, 171 as the consequences of coating loss become more critical with increasing reliance on their continued protection. No present material meets both the toughness and CMAS resistance requirements over the relevant range of temperatures.…”

Bending fracture behavior of freestanding (Gd0.9Yb0.1)2Zr2O7 coatings by using digital image correlation and FEM simulation with 3D geometrical reconstruction

“…However, its phase transformation and sintering result in a poor performance when the service temperature exceeds 1200 ℃ [4]. Therefore, in recent years, many researchers developed rare-earth doped zirconia and zirconate TBCs, such as ScGdSZ [5], La 2 Zr 2 O 7 [6,7], and Gd 2 Zr 2 O 7 [8][9][10][11][12][13]. Zhang et al [14] systematically investigated the thermophysical properties of Yb 2 O 3 doped Gd 2 Zr 2 O 7 and obtained many interesting results.…”