Nondestructive measurements of residual stress in air plasma‐sprayed thermal barrier coatings

Abstract

There is a demand for more efficient and powerful gas turbines, which are characterized by higher operating temperatures, longer lifetimes, and other features. 1-3 This demand has led to great challenges in the development of advanced thermal protection technologies, among which thermal barrier coatings (TBCs) are regarded as one of those most promising to meet the demand. 4-8 Typically, TBCs consist of the following four layers 5,6 : (i) the superalloy substrate, which is the main load-bearing constituent; (ii) the ceramic top coat (TC), which is usually composed of 6-8 wt.% yttria-stabilized zirconia (YSZ) and acts as a temperature insulator; (iii) an aluminum-containing bond coat (BC) between the substrate and the TC, which is usually composed of MCrAlY (where M is Ni and/or Co) and used for alleviating the thermal expansion mismatch stress between the aforementioned two layers; and (iv) a thermally grown oxide (TGO), which forms between TC and BC when they are exposed to high temperature and provides oxidation resistance. Each of these constituent layers presents marked differences in physical, thermal, and mechanical properties, and all contribute to determine performance and durability. Typically, the TBCs are fabricated using either electron-beam physical vapor deposition

Comparison and Selection of Data Processing Methods for the Application of Cr3+ Photoluminescence Piezospectroscopy to Thermal Barrier Coatings

“…In 2019, Shen et al [22] measured the compressive stress of TGO under thermal shock cycles and found that the evolution of the TGO microstructure, cracks, residual stress and element depletion appeared to be relevant to the durability and degradation of TBCs. In 2020, Jiang et al [23] verified that the residual stress evolution of TGO for air plasma spraying TBCs can be effectively used to indicate interfacial delamination.…”

“…The evolution of thermal oxidation stress in TGO was studied by Manero et al [26] using the Psd-Voigt fitting function, and the stress detected ranged from approximately 2 to 4 GPa throughout the loading history, with a standard deviation of approximately 78 MPa under the same loading conditions. Jiang et al [23] employed a Lorentzian curve algorithm to fit the spectrum obtained from TGO and determined the peak position, and the average stress gradually increased from 1.76 GPa until a peak value of approximately 3.45 GPa was reached. Shen et al [22] discovered that the compressive stress of TGO with a LZC/YSZ top coating reached the highest value of 2.56 GPa at 1000 thermal cycles, but the data processing method was not mentioned.…”

“…Therefore, only high-resolution stress characterization can sufficiently explain the dynamic evolution mechanism of TBC delamination, which has been effectively presented by the latest numerical model [29]. However, among all the published works, the residual stress measured in TGO varied by at least tens of MPa, which ineluctably made accurately determining the evolution tendency difficult because of the low resolution of the stress measurement [22,23].…”

YAG:Ce 3+ piezo‐spectroscopy: A high‐sensitive method used for stress characterization of thermal barrier coating

“…This method has the advantages of a high spatial resolution, a nondestructive nature, and high‐speed detection 5–7 . For the stress characterization of the TGO layer, the ruby fluorescence method is the most applicable, 6–10 and for the stress characterization of the specific area inside the ceramic layer, the rare‐earth fluorescence method is usually used 5,11,12 . For example, Jiang et al.…”

Effects of Roughness on Stresses in an Oxide Scale Formed on a Superalloy Substrate

“…During oxidation of high temperature alloys, e.g., Ni based superalloy and FeCrAl alloy, the stress in the oxide scale formed on the substrate plays an important role in spallation of the oxide scale. Thermally grown oxide (TGO), mostly alumina, forms in thermal barrier coatings (TBCs), when TBCs are exposed to high temperature environment; and spallation of TGO leads to failure of TBCs [1][2][3][4][5][6][7][8]. It is generally agreed that the stress in TGO varies with the undulating morphology of the oxide scale [9].…”