Laser thermal gradient testing of air plasma sprayed multilayered, multi‐material thermal barrier coatings

Abstract

Air plasma sprayed (APS) thermal barrier coatings (TBCs) are a widely used technology in the gas turbine industry to thermally insulate and protect underlying metallic superalloy components. These TBCs are designed to have intrinsically low thermal conductivity while also being structurally compliant to withstand cyclic thermal excursions in a turbine environment. This study examines yttria-stabilized zirconia (YSZ) TBCs of varying architecture: porous and dense vertically cracked (DVC), which were deposited onto bond-coated superalloys and tested in a novel CO 2 laser rig. Additionally, multilayered TBCs: a two-layered YSZ (dense + porous) and a multi-material YSZ/GZO TBC were evaluated using the same laser rig. Cyclic exposure under simulative thermal gradients was carried out using the laser rig to evaluate the microstructural change of these different TBCs over time. During the test, real-time calculations of the normalized thermal conductivity of the TBCs were also evaluated to elucidate information about the nature of the microstructural change in relation to the starting microstructure and composition. It was determined that porous TBCs undergo steady increases in conductivity, whereas DVC and YSZ/GZO systems experience an initial increase followed by a monotonic decrease in conductivity.Microstructural studies confirmed the difference in coating evolution due to the cycling.

The correlation of the scattering coefficient and morphology‐based microstructure in yttria‐stabilized zirconia coatings

“…Figure 2 shows the SEM images of as‐sprayed state and after the 50‐h laser rig test state of the YSZ coating. The detailed APS spray parameters and powder info are given in Wu et al., 26 as well as the testing conditions. After 50 h of thermal cycling, IP and IC have reduced in number and size due to sintering, whereas vertical cracks formed at the top surface.…”

Experimental and numerical life evaluation of TBCs with different BC and diffusion coating under cyclic thermal loading

“…Thermal barrier coatings (TBCs) are multilayered systems applied to gas turbine engine components to increase their operating temperature and lifetime. 1,2 TBC systems usually consist of four different layers. These layers include the superalloy substrate, metal bond coat (BC) layer, thermally grown oxide (TGO), and ceramic top coat (TC) layer.…”

“…In the aforementioned studies, the focus has been on investigating the effect of TGO thickness, creep, and the material of layers on the failure of coatings under thermal cycle conditions and the impact of parameters such as the thermal spraying method (APS and HVOF), twolayer BC, diffusion coating, and the TC absence on the TGO growth and lifetime of the coatings has not been studied. For this reason, in this article, to increase the lifetime of TBCs under cyclic loading, the effect of APS-BC, 1 HVOF-BC, two-layer BC, diffusion coating, and the TC absence on the TGO growth and lifetime of the coatings have been investigated. Moreover, in the finite element models created in the conducted studies, the interface geometry is considered simple sinusoidal or semicircle functions, and the TC porosity is neglected due to the complexity of the geometry.…”

“…Thermal barrier coatings (TBCs) are multilayered systems applied to gas turbine engine components to increase their operating temperature and lifetime 1,2 . TBC systems usually consist of four different layers.…”