Study On The Strength Of Thermal Barrier Coatings Under CMAS Penetration With The Effect Of Cooling Hole Structure

As a widely used thermal protection method in the hot components of gas turbine,thermal barrier coatings(TBCs)have good thermal insulation,corrosion resistance and oxidation resistance.The peeling failure of the TBCs causes the components exposed to the high temperature gas,which seriously affects the safety of the gas turbine.The increasingly harsh working environment in gas turbine has brought many new failure mechanisms to TBCs,one of which is calcium magnesium aluminum silicate(Ca O-Mg O-Al₂O₃-Si O₂,CMAS)deposit.CMAS melts at high temperatures,and penetrates into the TBCs through the pores on the surface,changing the thermal/mechanical properties of the ceramic layer,and finally causing the failure of TBCs.The nonuniform penetration of CMAS may cause complex temperature distribution in TBCs,which would further affect the interface strength of the TBCs.In addition,the complex temperatur e gradient and structure effect near the cooling holes may aggravate the influence of CMAS penetration on the strength of TBCs.Therefore,this paper uses a combination of theory-experiment-numerical calculation to carry out the strength analysis of the thermal barrier coating under CMAS penetration,and conducts an in-depth study considering influence of the coupled cooling structure.The research contents are as follows:First,a finite element model considering the micro-structures of the ceramic layer was established,and the effects of CMAS penetration depth,micro-structure shape,thermal cycle load,and creep time on the stress and cracking behavior in the ceramic layer were studied.The results show that the stress state around CMAS penetration interface is the most dangerous,and cracks will initiate from the edges of those CMAS filled micro-structures.Thermal mismatch induced cracking is more likely to occur inside the ceramic layer in the early stage of CMAS penetration In addition,CMAS penetration can cause cracks to grow more easily near the sharper transverse pores.The thermal cycle load increases the residual stress around the micro-structures infiltrated by CMAS,which may accelerate the cracking failure of the ceramic layer.Secondly,based on the observation results of the CMAS distribution on the surface of the in-service blade,and a multi-periods model under CMAS uneven penetration into TBCs was established while the temperature gradient and interface roughness were are considered,and the effect of the CMAS uneven penetration on the interior of the thermal barrier coating was developed.As a result,the uneven penetration of CMAS on the surface results in a lateral temperature gradient inside the thermal barrier coating,uneven growth of TGO,and an uneven stress distribution at the interface.The deeper the penetration depth of CMAS is,the worse the interface stress state is,which may accelerate the initiation and propagation of interface cracks;the interface roughness causes the change of interface stress.Thirdly,based on the observation from the experiments,the numerical model of TBC-film cooling system with or without CMAS penetration was established to investigate the influence of CMAS penetration coupling cooling hole structure on the strength of TBCs.The results show that the different interface morphologies at the edge of the cooling hole will affect the stress concentration around the cooling hole.The penetration of CMAS will increase temperature and thickness of TGO at the interface,resulting in mixed type cracks in the interface at the front edge of the cooling hole,and pure type?cracks on both sides of the cooling hole.