MCrAlY/8YSZ热障涂层高温水氧腐蚀行为研究OA

To investigate the impact of the high temperature water vapor environment on the corrosion behavior of MCrAlY/8YSZ thermal barrier coatings(TBCs),high-velocity oxy-fuel(HVOF)spray and atmospheric plasma spray(APS)are employed to prepare metal bond coatings with different structures and compositions on MM247 substrates.Subsequently,8YSZ ceramic coatings are deposited onto each bond coating via APS to fabricate TBC systems with varying metal bond coating characteristics.The TBCs with different bond coating structures/compositions are subject to high-temperature water vapor corrosion tests at 1050℃with water vapor contents of 0vol.%,45vol.%,and 80vol.%,respectively.The corrosion behaviors of TBCs under these different conditions are compared,and the microstructure and composition of the corrosion products are analyzed for each system using SEM equipped with an EDS.The results indicate that after exposure to the water vapor corrosion tests at 1 050℃with varying water vapor contents,the dual-layer oxide scale composed of spinel oxide and Al2O3 is observed on each TBC sample.The continuous and dense microstructure of the Al2O3 layer results in a slower growth rate.This continuous and dense structure effectively slows the outward diffusion of metal ions within the bond coating,thereby inhibiting the growth of the TGO layer.In contrast,the spinel oxide exhibits inconsistent growth with internal porosity.Its greater brittleness and accelerated growth rate readily induce crack initiation within the TGO layer,leading to premature failure of the thermal barrier coating system.Therefore,controlling the content of spinel oxide within the TGO layer is critical for extending the service life of thermal barrier coatings.In high temperature water vapor environments,spinel oxide formation is accelerated,thereby hastening the corrosion of the bond coating.An increase in water vapor content further promotes this process.A dense bond coating structure can effectively slow the outward diffusion of metal ions during high temperature water vapor corrosion,reducing the proportion of spinel oxide in the corrosion products and thus improving the water vapor corrosion resistance of the TBCs.In contrast,bond coatings prepared by atmospheric plasma spray inherently contain a certain level of porosity.These pores not only provide pathways for corrosive media to penetrate the bond coating,but also act as low-activation-energy diffusion paths for metal ions when they migrate outward to form corrosion products upon contact with the corrosive environment.Consequently,the pores serve as rapid diffusion channels for the outward diffusion of metal ions,ultimately accelerating the formation of corrosion products.In contrast,a single-layer bond coating produced by HVOF spray enables molten metal particles to impact the substrate with higher kinetic energy,resulting in a denser microstructure and a reduced formation rate of corrosion products.Furthermore,the incorporation of Ta into the bond coating further reduces the outward diffusion rate of metal ions,consequently inhibiting the growth rate of the spinel oxide under high temperature water vapor conditions.The Ta element segregates at elevated temperature,accumulating preferentially at grain boundaries and phase boundaries.These sites act as critical channels for the outward diffusion of metal ions during oxide scale growth.When Ta becomes enriched at these boundaries,the outward diffusion of metal ions is suppressed.As a result,the growth of the oxide layer becomes dominated by the inward diffusion of oxygen ions.However,the inward diffusion rate of oxygen ions is lower than the outward diffusion rate of metal ions,leading to an overall reduction in the oxide layer growth rate.