Laser re-melting assisted with induction heating of yttria partially stabilized zirconia thermal barrier coatings

Laser re-melting of thermal barrier coatings (TBCs) results in certain issues, such as surface segmented network cracks, surface crater and low processing efficiency. In this study, laser re-melting of Zr02-7wt% Y2O3 using a pulsed laser with and without induction preheating was investigated. A wide variety of TBCs surface temperatures were attained by the induction heater before laser re-melting. The laser re-melted samples were investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD). It was observed that the utilization of induction preheating can effectively decrease the threshold laser energy (30% of peak power, 67.9J/cm^2) of fully re-melting TBCs with relatively less crack density compared to without the application of it (35% of peak power, 79.2 J/cm^2). It was found that some longitudinal cracks distributed along the re-melted/un-melted interfaces without the application of preheating or at low surface temperatures (below 900°C) while disappeared when heated to higher temperatures (above 900°C) due to it helps developing relatively steadier melt temperatures as well as decreasing the cooling rates between molten pool and un-melted coating and consequently the thermal gradient during the subsequent re-melting process. XRD results indicated that the enhanced surface temperature can decrease the content of monoclinic phase.