Microstructural characterization of modified plasma spray LZ/YSZ thermal barrier coating by laser glazing

Abstract

One of the high potential material, lanthanum zirconate (LZ) is deposited on superalloy 625 due to its excellent phase stability, low thermal conductivity as well as the high melting point. However, microstructural defects were detected due to lamellar structure behaviour exhibited from the plasma-sprayed coating techniques. This paper investigated the effect of surface modification on LZ thermal barrier coating (TBC) by using laser glazing method. The double ceramic layer (DCL) TBCs are composed of NiCoCrAlYTa bond coating formed via the HVOF process while 8YSZ ceramic top coat and La2Zr2O7 as the third layer were produced by utilizing the APS technique. Nd:YAG pulsed laser has been used to modify the surface layer of plasma-sprayed LZ coatings. The microstructural morphologies of both as-sprayed and laser glazed samples were investigated using Scanning Electron Microscopy (SEM). The phases of the coatings were analysed with X-ray Diffractometry (XRD). The results showed that the laser glazing process reduced surface roughness attributed to the sealing of porosities and other structural defects of the coating. Finally, the impacts of laser energy input and laser distance on the characterization of the glazed layer are discussed.