Deposition Characteristics And Corrosion Mechanism Under Water Vapor Of Yb₂SiO₅ Environmental Barrier Coatings

Silicon carbide fiber composite provides a wide range of growth space for the manufacturing and performance improvement of aerospace equipment.However,although the addition of fiber phase reduces brittleness,it brings serious risks of oxidation and ablation in service under high temperature,especially easy to be degraded and corroded at the high temperature water vapor environment,resulting in a sharp decline in service performance.The way to solve this problem is to conduct thermal protection treatment on fiber-reinforced ceramic matrix composites?CMC?,including modification of matrix materials,preparation of sealing coatings and other technologies.Among them,environmental barrier coatings?EBC?with good bonding strength,high temperature resistance,oxidation resistance and ablative resistance are necessary means to improve the performance of components.In this paper,the third-generation Yb₂SiO₅rare-earth silicate EBC was used as the research material,and the new thermal spraying technology-plasma spraying-physical vapor deposition?PS-PVD?and traditional atmospheric plasma spraying?APS?were used to prepare the coating.The coating structure evolution of Yb₂SiO₅at high temperature was investigated.The failure forms and mechanism of coating at high temperature vapor environment were analyzed through typical thermal cycling and water vapor corrosion tests.Through the above research work,the deposition mechanism of Yb₂SiO₅prepared by PS-PVD and the failure mechanism of Yb₂SiO₅coating under high temperature and water vapor environment were obtained,which provided theoretical guidance for subsequent material development and process control.The main results of this paper are as follows through the experimental characterization:?1?PS-PVD can prepare dense coating,and the deposition of Yb₂SiO₅environmental barrier coating which is mainly gas-liquid two-phase deposition.Compared with the inclusion of non-melted particles and cracks in the APS coating,the coating quality is significantly improved.However,under high power and low pressure conditions,Yb₂SiO₅will generate thermal phase transition and decomposition,forming a high-temperature unstable phase structure.?2?The thermal cycling experiment at 1300?showed that the Yb₂SiO₅prepared by PS-PVD has better thermal shock resistance.In the sample experiment of the same matrix,no obvious peeling occurred after 30 water quenching cycles,while the edge peeling occurred after 15 times of APS sample.At the same time,a small amount of loose Si C_f/Si C CMC coating samples peeled off after 35 cycles,while the dense matrix had cracked directly and failed after 35 cycles due to the accumulation of internal thermal stress.The influence of different dense matrix on thermal shock is also great,which is more conducive to the release of thermal stress in the process of thermal cycling than the loose matrix.?3?The results of constant temperature oxidation experiment at 1300?showed that the chemical compatibility between Al₂O₃and Yb₂O₃or Yb₂SiO₅in Mullite was poor,and the rod-shaped Yb₃Al₅O₁₂phase was generated in the Mullite layer,resulting in the lamination of mullite and peeling of the coating.?4?The vapor corrosion behavior of Yb₂SiO₅at 1300?was investigated.The results showed that Yb₂SiO₅was slowly corroded in the corrosion process.The dense coating prepared by PS-PVD provided thermal protection to the substrate for 200 h or more.However,as the decomposition products of Yb₂SiO₅were dispersed in the coating,a large number of holes were formed after water vapor corrosion,which damaged the structural integrity of the coating.APS Yb₂SiO₅did not produce a large number of holes in the coating during the corrosion process.However,due to its loose surface,it significantly reduced the thinning after200 h of corrosion,which the rate was 0.02335?m/h.?5?At 1400?,the corrosion rate of Yb₂SiO₅coating was significantly accelerated,but due to the higher temperature,Yb₂SiO₅and the corrosion intermediate Yb₂Si₂O₇showed obvious grain growth.At the same time,the growth causes the surface defect to heal,resulting in the coating internal corrosion hole to reduce.As PS-PVD Yb₂SiO₅is a unilateral coating,there is a lot of droplet accumulation in the plate spraying process,so there is peeling phenomenon in the corrosion process,and the thinning rate is 0.0818?m/h.APS Yb₂SiO₅has the effect of slowing down the corrosion and peeling of the coating due to the accumulation of volatile products on the surface.