Optimization of laser process parameters and improved corrosion behaviour of LZ/YSZ thermal barrier coating

Abstract

Laser processing the surfaces of plasma-sprayed thermal barrier coatings is one of the methods used to improve the corrosion resistance of the coatings. However, laser glazing alone is not sufficient to fully protect coatings from corrosion. In this study, optimum laser surface modification parameters were determined for plasma-sprayed LZ/YSZ double-layer thermal barrier coatings. The coating surface, whose entire surface was scanned with optimum parameters, was modified with nano YSZ using the electrophoretic deposition technique. Thus, the network cracks formed during laser glazing were filled with nano YSZ. The coating modified by laser and electrophoretic deposition processes was subjected to corrosion tests. As a result of the characterizations, it was determined that the optimum laser surface modification parameters for LZ/YSZ thermal barrier coatings were 200 mm laser distance, 120 scan speed, and 28w laser power. With these parameters, discontinuities on the as-sprayed coating surface were eliminated. A dense layer was successfully created on the LZ layer. As a result of the corrosion tests, it was determined that modifying the laser-glazed surface with nano YSZ reduced the penetration depth of corrosive contaminants. Thus, the glassy melt and hot corrosion resistance of LZ/YSZ thermal barrier coatings was increased.