Sintering‐induced delamination of thermal barrier coatings by gradient thermal cyclic test

Abstract

Lifetime is crucial to the application of advanced thermal barrier coatings (TBCs), and proper lifetime evaluation methods should be developed to predict the service lifetime of TBCs precisely and efficiently. In this study, plasma‐sprayed YSZ TBCs were subjected to gradient thermal cyclic tests under different surface temperatures, with the aim of elucidating the correlation between the coating surface temperature and the thermal cyclic lifetime. Results showed that the thermal cyclic lifetime of TBCs decreased with the increasing of surface temperatures. However, the failure modes of these TBCs subjected to thermal cyclic tests were irrespective of different surface/BC temperatures, that is, sintering‐induced delamination of the top coat. The thickness of thermally grown oxide (TGO) was significantly less than the critical TGO thickness to result in the failure of TBCs through the delamination of top coat. There was no phase transformation of the top coat after failure. In contrast, in the case concerning the top coat surface of the failure specimens, the elastic modulus and microhardness increased to a comparable level due to sintering despite of the various thermal cyclic conditions. Consequently, it is conclusive that the failure of TBCs subjected to gradient thermal cyclic test was primarily induced by sintering during high‐temperature exposure. A delamination model with multilayer splats was developed to assist in understanding the failure mechanism of TBCs through sintering‐induced delamination of the top coat. Based on the above‐described results, this study should aid in facilitating the lifetime evaluation of the TBCs, which are on active service at relatively lower temperatures, by an accelerated thermal cyclic test at higher temperatures in laboratory conditions.

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].…”

Erosion Resistance and Damage Mechanism of TiN/ZrN Nanoscale Multilayer Coating

“…A thick and hard ceramic coating of up to >1 mm can be deposited by plasma spraying with a lamellar structure [15,16]. However, the plasma-sprayed coatings possess a relatively lower erosion resistance than the bulk material due to its inter-splat pores [17][18][19]. This implies that a dense coating with a lamellar structure might be effective for further design optimization of erosion-resistant coatings [20].…”

Preparation of Yttria-Stabilized Zirconia Hollow Sphere with Reduced Shell Thickness by Controlling Ambient Temperature during Plasma Process

“…It is widely thought that both the phase transformation of the metastable T' phase and the sintering-induced stiffening of the top coating would contribute to the failure of a typical YSZ top coating. However, the phase transformation from T' phase to the M + C phases needs a long and even incubation period at a very high temperature [15][16][17]. In addition, the sintering induced stiffening should be significant to a sufficient level before spalling failure, and this would allow a very long service lifetime, even at high temperatures [18][19][20][21][22][23][24][25][26][27].…”