Abstract
Hybrid plasma spraying combined with YAG laser irradiation was studied in order to obtain the optimum zirconia coatings for thermal barrier use. Zirconia coatings of approximately 150 ;Um in thickness were formed on the NiCrAlY under coated steel substrates both by means of conventional plasma spraying and hybrid plasma spraying under a variety of conditions. Post-laser irradiation was also conducted on the plasma as-sprayed coating for comparison. The microstructure of each coating was studied in detail and, for some representative coatings, thermal barrier properties were evaluated by hot erosion and a hot oxidation test. With hybrid spraying, performed under optimum conditions, it was found that a microstructure with appropriate partial densification and without connected porosities was formed and that cracks, which are generally produced in the post-laser irradiation treatment, were completely inhibited. In addition, hybrid spraying formed a smooth coating surface. These microstructural changes resulted in improved coating properties with regard to hardness, high temperature erosion resistance and oxidation resistance. Keywords: Hybrid spraying, YAG laser, Plasma-spraying, Thermal barrier coating, Zirconia, NiCrAlY, Densification, Hot-erosion resistance. Oxidation resistance, Roughness.
