Preparation Of Al-Ti-YSZ Thermal Barrier Coatings And Mechanism Of CMAS Mitigation

Thermal barrier coatings?TBCs?are widely used in hot section components of engine to improve the life of engine,reduce fuel consumption and improve efficiency.However,when a turbine operates in a harsh environment,it is inevitable to ingest the calcium-magnesium-aluminum-silicon particles?CMAS?in the air.These particles are melted on the thermal barrier coatings at high temperatures and penetrated into the coating along pores and microcracks.Resulted in the composition,structure and properties of the coating are degraded,and eventually the coating premature failure.The 7YSZ thermal barrier coating,which is currently the most widely used,is highly susceptible to corrosion damage by CMAS.Therefore,it is necessary to study how to improve the thermal barrier coating resistance to CMAS corrosion without damaging other excellent properties of the coating.Based on this,the YSZ was modified by Al₂O₃ and TiO₂,and the composition design,mechanical properties and CMAS corrosion resistant mechanism of the coatings were systematically studied.The main contents of research and results are as follows:Firstly,the composition of YSZ coating materials with different contents of Al₂O₃ and TiO₂ were designed,and the phase composition of the materials,the high temperature corrosion of CMAS and the thermal properties after modification were studied.The results show that the corrosion of CMAS destroys 7YSZ and causes the delamination of the microstructure and phase transformation.After modification by Al₂O₃ and TiO₂,as the content of Al₂O₃ increases,the penetration depth of CMAS decreased and a chemical reaction occurs to formed anorthite.Al₂O₃ precipitated at1300°C,which causes the thermal conductivity of the modified YSZ to increase as the Al2O3 content increased.Combined with the corrosion damage of CMAS and thermal properties of the composite coating materials,selected 10 mol%Al₂O₃ and 5mol%TiO₂ modified YSZ as coating materials to improving the corrosion resistance of CMAS.Secondly,10 mol%Al₂O₃ and 5 mol%TiO₂ modified YSZ?10A5TYSZ?and7YSZ thermal barrier coatings were prepared by APS method,and their phase stability and mechanical properties were characterized.The results show that the as-sprayed and the high temperature heat treatment maintain the non-transformed t-ZrO₂ phase,and the Al₂O₃ and TiO₂ were not precipitated in 10A5TYSZ coatings.When Al₂O₃ and TiO₂ were added into YSZ,the Young's modulus,hardness and fracture toughness of coatings were increased.Thirdly,CMAS/TBCs interaction with CMAS at high temperature was studied.The CMAS resistant mechanism of 10A5TYSZ was discussed by microstructure,penetration depth and chemical reaction product characterization.The results show that CMAS can quickly penetrated the entire 7YSZ coating at high temperature,which causes the microstructure of the coating to change and induced the t-m phase transition.The rate of CMAS penetration into the 10A5TYSZ coating is significantly slowed down,and the damage of the coating is reduced.This is because that the addition of Al₂O₃ and TiO₂ can promote the formation of anorthite phase when the CMAS interacted with 10A5TYSZ TBCs at high temperature.Anorthite can increased the melting point of CMAS and blocked the infiltration pathway,thereby alleviating the corrosion damage of CMAS.