Abstract
Thermal barrier coatings (TBCs) are used in advanced engines working at higher temperatures. Higher efficiency and performance of gas turbine engines will require careful selection of TBCs. In this study, Ni22Cr10Al1.0Y (Amdry 9625) bond coat and two types of top coat including ceria stabilized zirconia (CSZ) ZrO2-24CeO2-2.5Y2O3) and yttria stabilized zirconia (YSZ) ZrO2-8Y2O3 were deposited on IN 625 by air plasma spraying (APS). The thickness of the duplex ceramic coat based on zirconia was in the range between 350 to 400 µm. The effect of high power Yb:YAG solid state laser at different laser parameters on feature, microstructure and roughness of plasma sprayed and laser sealed coating of multilayer ceria stabilized zirconia/ yttria stabilized zirconia was investigated. Surface roughness has been reduced significantly after laser sealing. The effect of laser process parameters carried out using Taguchi’s L16 orthogonal array design. Minimum roughness can be obtained at moderate power density and longer interaction time with sufficient specific energy to produce complete melting of coating. Characterization and analysis of results was achieved by employing scanning electron microscopy (SEM) , (EDS) and image J analysis. It was found from the results, there were significant improvements in the performance of plasma sprayed coatings after laser sealing due to the reduction of surface coating defects.
Highlights
The hot metallic sections used in the turbine industries, power generation, marine and aerospace applications are often coated with thermal barrier coating to protect them from aggressive environment [1]
The surface morphology of plasma sprayed thermal barrier coating is sign of in Figure 2 at low and high magnification. Different features such as voids, microcracks and protrusions, which is typical phenomenon for air plasma sprayed TBCs. These features formed in the ceramic top coatings due to thermal stresses induced during rapid cooling rate generated after coating process
The energy dispersive X-ray spectroscopy (EDS) analysis reveals the elemental composition of the top ceramic coat in Figure 3 which composed of zirconium, yttrium and oxygen
Summary
The hot metallic sections used in the turbine industries, power generation, marine and aerospace applications are often coated with thermal barrier coating to protect them from aggressive environment [1]. TBCs comprise of three layers: a ceramic top coat, a metallic bond coat and Ni- base super alloy substrate [2, 3]. Laser sealing providing a dense layer and modified microstructure, resulting in reduction of surface roughness considerably. It produce surface free from porosity and form continuous network of crack perpendicular to the surface which improve the strain accommodation [14]. Present work concentrate on using high power solid state laser type Yb:YAG for sealing multilayer of TBCs consist of CSZ YSZ as ceramic coat. Study the effect of laser treatment on the surface roughness of plasma sprayed thermal barrier coating. As well as study the alteration of laser processing parameters on the obtained roughness using design of experiment by Taguchi methods
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