Effect of Thermal Growth Oxide Composition and Morphology on Local Stresses in Thermal Barrier Coatings

Abstract

The failure of thermal barrier coatings (TBCs) during operation depends mainly on the thermal mismatch between the ceramic top coat (TC) and the metal bond coat (BC). The thermal mismatch at the interface is influenced by the dynamic changes in the composition and morphology of the thermally grown oxide (TGO) between TC and BC during thermal cycling. This work focuses on the establishment of a TGO dynamic growth model, which considers the changes in TGO composition and morphology for investigating the effect of dynamic growth of TGO on local mismatch stresses during thermal cycling. The results show that the sharp locations at the TGO/BC interface are more prone to high tensile stresses during thermal cycling due to the uneven growth behavior of TGO, leading to crack initiation. The valley region of the interface is in a state of compressive stress σxx during the early stages of thermal exposure. The peak region preferentially forms a concentration of tensile stress σyy. Once large-scale “layer” (Ni, Co)Al2O4-based spinel-like mixed oxides(MO) growth occurs in TGO, the stress σxx changes from compressive stress to tensile stress in the valley region, eventually forming high tensile stress (Max: +158 MPa). The maximum tensile stress σyy in the peak region is increased to 256 MPa, which is more than two times larger than the early period of thermal exposure. As a result, the dramatic changes in local stresses seriously affect the time and location of microcracks.

Experiment and Numerical Simulation on Thermal Cycling Performance of YSZ-Based Sealing Coatings with “Brick-Mud” Layered Structure

“…The average values of the maximum surface height (Sz), maximum peak height (Sp), maximum valley depth (Sv), and arithmetic mean height (Sa) were 107.5 µm, 56.9 µm, 50.6 µm, and 11.6 µm, respectively. For the convenience of obtaining general rules, the interface was simplified as a cosine wave [25]. A point analysis was conducted on the profile to obtain the average value of peak-to-valley distances, and the designed cosine wave possessed a wavelength of 100 µm and an amplitude of 11.6 µm.…”

A Comprehensive Understanding of Thermal Barrier Coatings (TBCs): Applications, Materials, Coating Design and Failure Mechanisms

“…where δ 2 is the TGO layer thickness, k p represents the growth rate constant of TGO (measured in [µm 2 /h and influenced by the oxidation system and BC constituents) and t is the oxidation exposure time [193,194]. The growth rate of the TGO is not constant over time; instead, it decreases with its thickening due to the accumulation of protective oxides that hinder oxygen diffusion toward the BC [91].…”

“…Spallation can occur at both the TC/TGO interface and the TGO/BC interface. Typically, a thicker TGO layer may result in the displacement of the spallation plane toward the TGO/BC interface due to significantly higher residual stress in this region and reduced adhesion [194,201].…”

Failure Mechanism of Thermal Barrier Coatings on Nozzle Guide Vanes Fabricated from Nickel-Based Single-Crystal Superalloy under Gas Thermal Shock Conditions

“…Thermal barrier coatings (TBCs) are extensively employed on the crucial hot-end components of aircraft engines to enhance their service temperature and lifespan. During operation, these coatings must withstand the damaging effects of severe environmental conditions, such as high temperatures, pressures, corrosion, alternating cold and hot impacts, and foreign object impacts, leading to various possible failure modes [1][2][3][4][5].…”