Thermal Shock Resistance of ZrO_2-8wt.%Y_2O_3 Coatings Prepared by Plasma-Laser Hybrid Spraying Technique
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Thermal spraying techniques have been widely applied for the production of ceramic protection layers on metals used in various hostile environments. However, all sprayed coatings have defects such as connected pores and unmelted particles, which deteriorate coating properties. To improve the properties of sprayed coatings, many approaches have been undertaken, such as laser irradiation, seal sintering with liquid alloys and sol-gel infiltration techniques. Lasers are promising technological tools due to speedy treatment and simplicity of process control. Moreover, laser treatment technology enables not only the post-treatment but also the pre and simultaneous treatment by combining with spraying process. TBC consisting of yttria partially stabilized zirconia layer and MCrAlY bond coating have been widely used to improve the performance of hot-section components used in gas turbines. To improve the lifetime of TBC coatings, post treatments of sprayed coatings and simultaneous spraying processes by plasma laser hybrid technique were tried. A technique using a low-viscosity resin with a fluorescent dye under a high vacuum has been tried for the accurate observation of microstructure of TBC coatings prepared by post laser treatments and laser hybrid spraying process. As a result of water quenching tests, coatings prepared by post laser treatments and laser hybrid spraying processes showed significantly improved thermal shock resistance compared with as-sprayed coatings. The relation of thermal shock resistance and microstructure of TBC coatings were evaluated by the careful observation of samples prepared by a vacuum infiltration technique with a low-viscosity resin and a fluorescent die.
- Trans. JWRI
Trans. JWRI 30 (1), 91-97, 2001