Study On High Temperature Performance And Failure Mechanism Of 8YSZ And La₂Zr₂O₇/8YSZ Thermal Barrier Coatings

Thermal barrier coatings(TBCs)has been widely used in aeroengine hot end components because of its excellent adiabatic performance and high temperature oxidation resistance.By adding barrier coating,anti-corrosion coating or diffusion barrier coating on single-layer TBCs to form double-layer TBCs,the anti-corrosion,anti-oxidation and other properties of double-layer TBCs can be effectively improved.Therefore,double-layer TBCs have received more and more concerns in recent years.In order to reveal the formation and growth mechanism of thermal growth oxides(TGO)in single-layer TBCs and double-layer TBCs during high temperature oxidation and thermal shock,two kinds of TBCs were prepared by air plasma spraying,whose ceramic coating were Y₂O₃stabilized Zr O₂(YSZ)and La₂Zr₂O₇(LZ)/YSZ,respectively.Subsequently,the two TBCs were oxidized and thermal shocked at 1100?.The experimental results show that diffusion kinetics of elements in bonding coating of LZ/YSZ TBCs was changed due to better ability to isolate external oxygen of LZ ceramic coating.Accordingly,the formation of SC was delayed.And La³⁺can affect the phase transformation of TGO,i.e.reduce the transition rate from metastable phase?-Al₂O₃to stable phase?-Al₂O₃,thereby reduce the residual stress in TGO.Therefore,LZ/YSZ TBCs exhibited superior high temperature oxidation resistance to YSZ TBCs.In addition,the strain energy release rate G of LZ/YSZ TBCs is higher than that of YSZ TBCs,which increases the tendency of delamination fracture,so thermal shock life of LZ/YSZ TBCs at1100?was lower than that of YSZ TBCs.And the main reason of thermal shock failure of LZ/YSZ TBCs is not TGO growth stress,but the difference of elastic modulus and thermal mismatch stress between ceramic coating LZ and YSZ.In order to explore the difference of CaO?MgO?Al₂O₃and Si O₂(CMAS)corrosion resistance and corrosion mechanism in high temperature and rainwater environment of YSZ and LZ/YSZ TBCs,CMAS corrosion resistance tests at 1200?and rainwater environment of two TBCs were carried out.Results demonstrate that after high temperature CMAS corrosion for the same time,due to phase expansion,ceramic coating volume shrinkage occurred on YSZ TBCs,thus surface cracks formed,which would lead to YSZ TBCs failure.While,compact apatite phases and fluorite phases formed on LZ/YSZ TBCs,the penetration of CMAS into ceramic coating was inhibited effectively.The residual stress of two TBCs corroded by CMAS is compressive stress,and the stress value of LZ/YSZ TBCs is smaller than that of YSZ TBCs.The electrochemical properties in simulated rainwater of two TBCs after high temperature CMAS corrosion showed that LZ/YSZ TBCs possessed higher free corrosion potential,lower corrosion current and higher polarization resistance than those of YSZ TBCs.Consequently,the presence of LZ ceramic coating effectively improved CMAS corrosion resistance in high temperature and rainwater environment of LZ/YSZ TBCs.In order to explore the influence of laser remelting on the high temperature performance of TBCs at 1100?.Subsequently,these two kinds of as-sprayed TBCs were remelted.Thereupon,high temperature oxidation and thermal shoch experiment was carried out.The results showed that the ceramic coating of two TBCs are more compact after remelting,it leads to external O was blocked.Thereby,the formation of SC was delayed.Consequently,laser remelting treatment can effectively improve the high temperature oxidation resistance of TBCs,and the high temperature oxidation resistance of the remelted LZ/YSZ TBCs was superior to that of the remelted YSZ TBCs.In addition,laser remelting improves the density of YSZ TBCs,the growth stress of TGO,and the thermal mismatch stress among ceramic coating,TGO and bonding layer were reduced.Therefore,thermal shock life of the remetled YSZ TBCs was obviously higher than that of the as-sprayed YSZ TBCs.And the thermal shock failure mode of the as-sprayed YSZ TBCs was severe buckling driving delamination with greater residual compressive stress on the surface,while that of the remetled YSZ TBCs was slight edge delamination with smaller residual compressive stress on the surface.