Laser sealing of plasma-sprayed calcia-stabilized zirconia

The use of ceramic barrier coatings is of growing interest, as turbines and other high-temperature components are required to work at increasing temperatures to achieve increased thermodynamic efficiency. For example, zirconia-based ceramic layers are applied to turbine blades by plasma spraying. Such coatings typically contain porosity but can be effectively used in service conditions; however, there are problems in relation to adhesion, mechanical strength and corrosion through cracks and interconnected pores. In the present investigation, the possibility of using laser radiation to seal the pores in calcia-stabilized zirconia (CSZ) coated steel has been explored. From the SEM observations and EMPA analysis, it is concluded that a laser beam at low specific energy can be effectively used to seal a thin layer and to weld the pores in as-sprayed ceramic layers used in high-temperature thermal barrier coatings. There is a refinement of the microstructure and improved uniformity of chemical composition, although some cracking occurs. 8 ref.--AA