Thermal Barrier Coating for Application to Light Weight Gas Turbine– A Review

Abstract

Hot section gas turbine implements are subjected to fluctuating stresses and temperatures within aggressive environments. It results in combined fatigue, creep and oxidation of constituent materials. Studies of different types of high temperature fatigue of nickel base superalloys help us to understand the causes of failure and expectations for the prediction of life. Generally nickel base superalloys are used in the form of single crystal, directionally solidified, powder metallurgy products, and polycrystalline cast/wrought alloys for different applications. The high temperature properties of these various forms make interesting usage within different high temperature and aggressive environments under stressed conditions. Gas turbines of either aerospace, electricity or diesel engine sectors are the consumers of these alloys. Thermal profiles of gas turbines are zones of interest for application. Considerations of lightweight philosophies to the implements reduce the section thickness. Therefore evaluation of fatigue for these alloys under stipulation of simulation bears more attention. Creep interposition into fatigue theories has become the basis of interpretation. Experiences to date belong to empiricism, where the formulations require introduction of many suitable variables according to the system of exposure. Application of thermal barrier coatings improves the performances of previous designs. Key failure areas of thermal barrier coatings are thermally grown oxide growth and ceramic coat sinter induced buckling and spallations. These coatings in practice appear in the form of thick, thin, and duplex, laser surface re-melted, functionally gradient materials, and microlaminations. The composite system of materials evaluation corresponds to the requirement of fatigue experiments for life prediction. The objective is to study the comparative behavior of nickel base superalloys under different conditions of fatigue and the influence of the thermal barrier coating (TBC). Different typesof fatigue mechanisms experimentally simulate components exposed to services because the variable for interrelation of the physical-thermal-chemical-mechanical phenomenon that prevails in such systems appears to be deficient. been made in the past two intervening decades in the understanding of the physical mechanisms of fatigue in Ni-base superalloys. This will be the subject of concern in the present paper; a systematic approach has been made to disentangle the separate combinations of different types of fatigue leading to fracture particularly in Ni-base superalloys.

Research on crack propagation behaviour of EB-PVD TBCs based on TGO evolution

“…In a high-temperature environment, oxygen reacts with Al, Co, and Ni in the metal bond coat, causing a change at the interface and internal oxidation. The increase in the oxidation degree leads to the formation and evolution of Al 2 O 3, layering of TGO (with α- Al2O 3 and Cr 2 O 3 ), formation of spinel phases (Ni(Al, Cr) 2 O 4 and NiO), and precipitation of elemental metallic phases (γ-Ni, α-Cr, γ-Al, β-Ti) 8 .…”