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5089 |
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Laser re-melting assisted with induction heating of yttria partially stabilized zirconia thermal barrier coatings |
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Rujia Wang / Department of Mechanical Engineering
Xi'an Jiaotong University, P.R. China Xia Dong/ State Key Laboratory for Manufacturing Systems Engineering, Xi2an,China Zhengjie Fan/ State Key Laboratory for Manufacturing Systems Engineering, Xi2an,China Kedian Wang/ State Key Laboratory for Manufacturing Systems Engineering, Xi2an,China Wenqiang Duan/ State Key Laboratory for Manufacturing Systems Engineering, Xi2an,China Xuesong Mei/ State Key Laboratory for Manufacturing Systems Engineering, Xi2an,China Wenjun Wang/ State Key Laboratory for Manufacturing Systems Engineering, Xi2an,China Jianlei Cui/ State Key Laboratory for Manufacturing Systems Engineering, Xi2an,China |
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Laser re-melting of ZrO2-Y2O3 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 ZrO2-7wt% Y2O3 using a pulsed laser with and without induction heating was investigated. A wide variety of TBCs surface temperaturesattained by utilizing the induction heater were monitored using an infrared thermometer. After that, the TBCs were treated by a Nd:YAG pulsed laser respectively. The microstructures and surface topographies of laser re-melted samples were investigated using scanning electron microscope (SEM) as well asconfocal laser scanning microscope(CLSM). The phases of the coatings were analyzed by X-ray diffraction(XRD).It was observed that the utilization of an induction heater 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). In addition, the crack density of re-meltedcoating surface with preheating shows a downward trend compared to that withnon-preheating. It also has been observed that some longitudinal cracks (along the laser scanning direction) distribute along the re-melted/un-melted interfaces without the application of induction heating or at the low surface temperature (below 900). While the longitudinal cracks disappear when the surface was heated to high temperatures (above 900) due to it helps developing a relatively steadier melt temperature as well as decreasing the cooling rates between the molten pool and un-melted coating and consequently the thermal gradient during the subsequent re-melting process. Microstructural analysis revealed a smoother surface profile in the preheated sample. XRD results indicated that the enhanced surface temperature can decrease the content of non-equilibrium tetragonal phase (T'). |