Thermal Barrier Coating System for Gas Turbine Application - A Review

Abstract

Ceramic coatings are refractory metal compounds deposited on substrates to reduce thermal loss and to protect components from high temperature. Thermal barrier coatings (TBC) are composite overlay of bond coat and ceramic coat on a superalloy substrate. reduce porosity of free surface and to increase glaze are other avenues to reduce diffusion of reactive gases and to increase internal heat transfer respectively. The former increases life of bond coat/substrate, whereas the latter increases energy efficiency by maximum utilisation of heat. The main unsolved problem is spallation of ceramic coating, which is cohesively induced in either side of interface and spread out to interfaces of adhesion. TBC increases life more than two-fold for cases of aerospace engines. However localised spallation may rise by high temperature corrosion of bond coat/substrate, TGO stresses, gaseous/liquid contaminant diffusion/ impregnation through tolerance networking of voids, and erosion.

Revestimentos para barreira térmica: evolução e perspectivas

“…Em muitos aspectos, a escolha de materiais e sua produção representam uma tecnologia de materiais já bastante madura. Mas existe uma percepção de que novos sistemas TBC serão necessários para atender as demandas de turbinas de última geração atualmente sendo projetadas [11,12].…”

Influence of isothermal and cyclic oxidation on the apparent interfacial toughness in thermal barrier coating systems

“…Even though TBCs allow drastic improvement of component performance and efficiency [1,2], thermal strains and stresses resulting from transient thermal gradients developed during in-service exposure limit the durability of the multi-material system. TBCs exhibit complex structure and morphology consisting of three successive layers, deposited or formed on the superalloy substrate ( Fig.…”

Optimized sol–gel thermal barrier coatings for long-term cyclic oxidation life

“…Thermal barrier coatings (TBCs) are widely used for various applications in turbojet engine gas turbines and combustion chambers in relation with their excellent thermal protection properties allowing drastic improvement of component durability and efficiency. 1,2 Typically, the overall thermal protection system includes: (i) the TBC itself, a ceramic top coat (TC) made of yttriastabilized-zirconia (YSZ) acting as thermal insulator, (ii) the superalloy substrate that supports mechanical loading, and (iii) an aluminium rich Bond Coat which enhances the cohesion between the substrate and the TBC and develops by oxidation a fine alumina film referred to as the thermally grown oxide (TGO). Within this multi-materials structure, each layer, characterized by specific physical, thermal and mechanical properties, shows -upon processing and "in-service" thermal exposuresdistinct thermomechanical behaviour, thereby resulting in the establishment of internal thermal stresses.…”

“…As a consequence, in highly complex TBC systems, failure mechanisms upon temperature cycling are very intricate and lots of theoretical as well as experimental research investigating mechanistic behaviours and microstructural mechanisms are dedicated to understanding the various processes of crack initiation and propagation, delamination and spallation. 2,3 Up to now, two main coating processes are used to deposit TBCs for industrial applications, namely the electron beam physical vapor deposition (EB-PVD) and the air plasma spray (APS), each generating specific layer morphology, deposit microstructure and thermo-physical properties.…”