Damage Detection of Thermal Barrier Coating by Ultrasonic Guided Wave

Nondestructive testing (NDT) of damage in thermal barrier coating (TBC) has received a wide attention for the inspection of aeronautic blade. Use of the ceramic material on top-coat which contains high temperature resistance, corrosion resistance and low thermal conductivity improve the ability to resist high temperature and corrosion of the metallic substrate. The bonding layer, however, is a source of weakness while has the beneficial effect of protecting the base. In this work, various forms of damage in bonding layer between nickel base and ceramic coating are investigated. Different shapes, sizes, positions and quantities of flaws are studied with the simulation of different detrimental reaction occurred in bonding layer. The dispersive characteristics of guided wave propagation in TBC is analyzed using finite element modeling (FEM) to simulate its propagation and scattering. Both time and frequency domain are conducted to study the change in different occasions. The aim is to verify if NDT can detect the damage in TBC with different sensitivity of various acoustic parameters to different types of flaws. Selections of appropriate acoustic parameters for quantitatively nondestructive test and evaluation, as well as location of thermal barrier coating defects are discussed.