Preparation And Study Of Sintering-resistant Structures Of Ceramic Layer Micro-core Shells For Thermal Barrier Coatings

Thermal barrier coatings（TBCs）,one of the three core technologies of combustion engines,are one of the main factors affecting the development progress of advanced high-efficiency combustion engines.The ceramic layer of in-service TBCs is mainly 7-8 wt%yttrium oxide stabilized zirconia（YSZ）.When its surface temperature is higher than 1250℃,the outer surface temperature is high and the sheet layer shrinks significantly due to intense sintering,while the sintering shrinkage of the sheet layer near the binder layer is small.This differential sintering shrinkage induces layer-by-layer spalling failure of YSZ flat particles.the lifetime of TBCs at1350℃ is only 17%of that at 1250℃.Based on this,this thesis investigated and prepared a double-shell hollow microstructured powder（inner shell YSZ and outer shell La₂Zr₂O₇）using a combination of experiments and simulations to investigate its formation mechanism and structural stability;based on high-temperature sintering tests,the high-temperature sintering resistance of the double-shell microstructured powder was investigated and the sintering resistance mechanism of the microstructured powder was elucidated.After high-temperature thermal exposure at 1200℃/200h,the porosity of the YSZ/La₂Zr₂O₇ mechanically mixed powder specimens was reduced by only 6%compared to the 18%reduction in porosity of the YSZ specimens,and the shrinkage rate was only 42%of that of the YSZ specimens,and the grain size was also significantly lower than that of the YSZ specimens.In addition,YSZ/La₂Zr₂O₇ mechanically mixed powder specimens still retain a large number of pores,and YSZ has been approximated as a bulk material.Therefore,the YSZ/La₂Zr₂O₇ heterogeneous interface can significantly improve the sintering resistance.Both chemical deposition and mechanical cladding methods can prepare core-shell structure powder with good cladding effect.The chemical reduction method using sodium dodecylbenzene sulfonate（SDBS）can deposit La₂Zr₂O₇ phase on the surface of YSZ particles,and the calcination process at 600℃/2 h is beneficial to maintain the cladding structure of La₂Zr₂O₇ shell layer.The mechanical cladding method was accomplished by plasma spraying.In this paper,the core-shell powder was prepared using three different angles（the angle between the YSZ beam and the La₂Zr₂O₇ beam）.During the preparation process,YSZ impinges on the molten La₂Zr₂O₇ droplets in solid form,and La₂Zr₂O₇ adheres to the surface of YSZ particles and solidifies to form the core-shell powder.The results show that the amount of cladding can be adjusted based on the angle change to prepare composite powders with different La₂Zr₂O₇contents.To gain a deeper understanding of the heterogeneous interfacial properties inside the core-shell structured specimens,a first-nature principle calculation analysis was used.The results show that the heterogeneous structure formed by the（011）face of the Zr O₂ cell and the（220）face of the La₂Zr₂O₇ cell has a low surface energy and can form a stable state.The electronic structure,elastic properties and binding energy were further analyzed,and it was determined that the heterojunction property is between metallic and nonmetallic,belongs to the trigonal system with the lowest symmetry,and the enthalpy of formation is less than 0,which is thermodynamically stable.In the ground state,the heterojunction has good mechanical stability,the interface exhibits ductility,the binding energy is negative,and the formation process of the interface between YSZ and La₂Zr₂O₇ is exothermic,which can form a stable heterojunction.After thermal exposure at 1200℃/200 h,the porosity,shrinkage,and particle size of the YSZ@La₂Zr₂O₇ core-shell powder specimens were basically the same for the three angles:the porosity decreased by about 10%and the shrinkage was about 2.45%,which was significantly lower than that of the YSZ specimens at 18%and 4.62%.In addition,the YSZ@La₂Zr₂O₇ core-shell powder specimens still retained a large number of pores,and the grain size did not change significantly,and were in the first three stages of sintering without severe sinter densification in the fourth stage.Therefore,YSZ@La₂Zr₂O₇ core-shell powder has significantly higher sintering resistance compared to YSZ and is a very promising material for ultra-high temperature TBCs ceramic layers.