Enhanced ablation resistance through laser glazing of plasma sprayed LaTi2Al9O19-based functionally graded thermal barrier coating

Abstract

The functionally graded (FG) thermal barrier coating of LaTi2Al9O19 (LTA) and 8% yttria stabilized zirconia (YSZ) over C263 Nickel alloy was deposited by air plasma spraying and NiCrAlY was used as a bond coat. Plasma sprayed samples were glazed using 3kW CW CO2 laser to produce dense and porous free surface layer to improve coatings ablation resistance. Duplex (DL) LTA/8YSZ coating was also fabricated for comparative studies. The coatings were subjected to hot combustion gas product of hydrogen fuel at a temperature of ~800°C and velocity of Mach 2 (680m/s) to evaluate their ablation behaviour. The phase composition and microstructure of the coatings were characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) analysis. It was observed that the laser glazing significantly reduced the surface roughness and improved the ablation resistance. The duplex layer was found porous and got detached completely because of thermal stress and volume expansion. Spallation of coatings occurred mainly due to shear force associated with hot gas. The laser glazed FG coating exhibited excellent ablation resistance and phase stability. It is concluded that the Laser glazing of FG LTA/YSZ is beneficial for better ablation resistance.