A comprehensive sintering mechanism for thermal barrier coatings‐Part III: Substrate constraint effect on healing of 2D pores

Abstract

During thermal exposure, the sintering of the plasma-sprayed thermal barrier coatings (PS-TBCs) is highly dependent on the healing of the two-dimensional (2D) pores (including the inter-splat pores and the intra-splat cracks), as reported in the previous Part-I and Part-II based on free-standing coatings. As a further study, this part aims to reveal the effect of substrate constraint on healing behavior of the 2D pores, since the coatings are actually bonded to superalloy substrate during real service. The healing of the 2D pores was quantitatively examined, and the multiscale mechanical properties were determined during the overall thermal exposure. In addition, a structure model was used to quantitatively correlate the evolution of 2D pores with mechanical property. The results of experiments and model prediction show that, different from the two-stage evolutionary trends in free-standing coatings, the overall evolution trends of microstructure and property can be divided into 3 stages affected by the substrate constraint. Moreover, the anisotropic healing of the 2D pores reported in free-standing coatings was enhanced significantly due to the additional stress in coatings resulting from constraint of substrate. This means that the healing of inter-splat pores became faster and severer. Given that, an outlook on structural tailoring to retard the performance degradation of TBCs was proposed. K E Y W O R D Sanisotropic healing kinetics, sintering, structural tailoring, substrate constraint, thermal barrier coatings

Thermophysical properties and cyclic lifetime of plasma sprayed SrAl12O19 for thermal barrier coating applications

“…In the stage Ⅰ (0-40 hours), the porosity of YSZ coating decreased rapidly which can be attributed to the healing of microcracks and small pores through multipoint connections ( Figure 3C). [48][49][50] During stage Ⅱ (40-1000 hours), the relatively wider pores and cracks decreased the possibility of multipoint connection, so the sintering speed is significantly lower. At the end of the annealing test (1000 hours), most of the microcracks and small pores cannot be observed and only large voids remained in YSZ coatings, resulting in a final porosity of about 5%.…”

The Evaluation of Durability of Plasma-Sprayed Thermal Barrier Coatings with Double-layer Bond Coat

“…Therefore, the difference between the durability of the two types of TBCs depended on other factors in the absence of TGO thickness. It has been well documented that the sintering [11][12][13][14][15][58][59][60][61], gradient thermal cycling temperature [16][17][18][19], and roughness of bond coat/topcoat interface [7,[20][21][22][23] also affect the durability of samples. In this case, these other factors were all identical in these two types of TBCs, except for the microstructures of the bond coats.…”

“…The spallation of the ceramic topcoat, typically made of yttria-stabilized zirconia (YSZ), is one of the factors that hinders the service of TBCs. The failure of atmospheric plasma-sprayed (APS) TBCs can be affected by many factors, such as TGO growth [1,2,[4][5][6][7][8], thermal expansion mismatch [1,[8][9][10], YSZ sintering [11][12][13][14][15], the temperature gradient across YSZ coating [16][17][18][19] and the profile of the bond coat surface [7,[20][21][22][23], etc. Thermal expansion mismatch between the YSZ coating and the substrate is one of the most critical factors that presently affects the durability of TBCs [9,10,19,24,25].…”

Key Problems Affecting the Anti-Erosion Coating Performance of Aero-Engine Compressor: A Review

“…This also implies that a typical way to obtain the smaller grain structure is to reduce the thickness of single layer. The interfaces are very dense, without presence of micro/nano-scale porosities or other phases [73][74][75][76][77].…”