Preparation Of Al₂O₃/SiO₂-YSZ Themal Barrier Coatings Based On Melting Point Engineering Mechanism And Study Of Its Volcanic Ash Corrosion-resistence Property

Thermal barrier coatings?TBCs?are widely used in high temperature components of turbine engines to reduce the temperature of hot air flow to the superalloy substrate.With the temperature of the inlet of turbine engine increasing,the service environment of thermal barrier coatings is getting harsher.During service,it is often corroded by dust,volcanic ash,etc.which are floating in the air and deposited on its surface.These materials are mainly mixture of calcium magnesium aluminum silicon?CMAS?.CMAS would melt and adhere to the surface of thermal barrier coatings when the surface temperature of the workpiece is higher than its melting point.CMAS attack would induce spallation and failure of TBCs,cause serious threat to the safety of turbine engine.In this study,the preliminary exploration study was carried out in powder form,then the Al₂O₃/SiO₂-YSZ thermal barrier coating was fabricated by electron beam physical vapor deposition technology and atmospheric plasma spraying process,and real volcanic ash was used to replace artificial CMAS as corrosives to simulate real service environment,carrying out high-temperature corrosion experiment.By characterizing and analyzing the experimental results,the mitigation mechanism of the sacrificial coating and the ability to mitigate volcanic ash corrosion were studied.The main research contents are as follows:?1?The Al₂O₃ and SiO₂ powders prepared by Sol-gel method and volcanic ash were analyzed for micromorphology,elemental composition and phase composition.The results showed that the composition and crystal form of Al₂O₃ and SiO₂ were close to ideal crystals.Compared with artificial CMAS,the composition and phase structure of real volcanic ash were more complex and closer to real corrosive substances.The thermal properties of volcanic ash and its mixture with Al₂O₃,SiO₂ and Al₂O₃-SiO₂were characterized.The results showed that the melting point of the mixtures were increased compared to volcanic ash,but with different degree of increase.Al₂O₃-SiO₂showed the relatively best effect,and Al₂O₃ and Al₂O₃-SiO₂ had the equivalent effect,while SiO₂ was the weakest.?2?The electron beam physical vapor deposition technique was used to deposit a columnar structure YSZ coating over the Ni Cr Al Y bond coat,and then Al₂O₃,SiO₂ and Al₂O₃-SiO₂ three types sacrificial overlayers were prepared on the top of YSZ layer using atmospheric plasma spraying.The micromorphology and element composition of Al₂O₃/SiO₂-YSZ coatings were characterized by SEM equipped with EDS.The results showed that the as-prepared YSZ coating and Al₂O₃,SiO₂,Al₂O₃-SiO₂ sacrificial coatings were in good morphology and structure,also,the composition conformed to the expected design.The combination between layers exhibited good adhesion.?3?Real volcanic ash was chosen to conduct high-temperature corrosion experiments,characterization and analysis of the samples were carried out with SEM,EDX and nanoindenter.The mechanism and performance of Al₂O₃/SiO₂ sacrificial coating to alleviate volcanic ash corrosion was further discussed.The results showed that the thickness of sacrificial coatings decreased as the corrosion time increasing.The penetration of volcanic ash did not occur on the Al₂O₃-YSZ sample,while Si slightly penetrated in the Al₂O₃-SiO₂-YSZ sample?originated from the sacrificial layer?,and approximately 80?m in the SiO₂-YSZ sample.The mechanical property characterization results showed that the Young's modulus change of Al₂O₃/SiO₂-YSZ thermal barrier coatings were relatively lower than the pure YSZ sample.Overall,the protective effect of Al₂O₃ layer was relatively optimal,while the level of Al₂O₃-SiO₂was the second,and the SiO₂ layer showed no obvious effect.