Crack-free surface sealing of plasma sprayed ceramic coatings using an excimer laser

Yttria stabilized zirconia coatings are typically used in the aerospace industry as high-temperature thermal barriers. These coatings are normally applied by plasma thermal spray, which has an inherent problem of producing coatings containing a substantial amount of open or closed porosity. Surface sealing of plasma sprayed ceramic coatings with CO2 and Nd:YAG lasers is always associated with the problem of cracking on melted layers. Although some attempts such as pre-heating have been used to overcome the problem, formation of cracking is still not prevented, especially in zirconia-based ceramic coatings. The present work investigates an alternative method of surface sealing of plasma sprayed 8 wt.% Y2O3–ZrO2 coatings using an excimer laser. The results show that smooth, crack-free and crater-free sealing can be obtained. Effects of laser operating parameters on the sealing quality and involved mechanism are also discussed.