The Preparation And CMAS Resistance Of Rare Oxide Thermal Barrier Coatings

The conventional 8YSZ thermal barrier coating cannot be long-term operated above 1200? because of the phase transformation and serious sintering,which will hinder the development of the future advanced aero-engine.In order to adapt to the higher operating temperature requirements of gas turbines,it is great significance to develop new TBC materials with high sintering resistance,low thermal conductivity,better thermal shock resistance and stronger corrosion resistance.Sm₂(Zr_0.7Ce_0.3)₂O₇?SZ7C3?and Gd₂(Zr_0.7Ce_0.3)₂O₇?GZ7C3?are important TBCs candidate materials due to extremely low thermal conductivity and sintering resistance.The paper studies the preparation methods and properties of SZ7C3 and GZ7C3 TBCs,the failure mechanism and high-temperature CMAS resistance of the coatings,as well as to explore the particle application of the rare earth oxides TBCs in the turbine blade engines.The SZ7C3 and GZ7C3 powders were synthesized by a traditional solid state reaction method,SZ7C3 and GZ7C3 show higher sintering resistance than 8YSZ.GZ7C3(0.41-0.57 W·m^-1·K^-1)coating and SZ7C3(0.59-0.70 W·m^-1·K^-1)coating have extremely low thermal conductivity and thermal expansion coefficients almost close to 8YSZ.GZ7C3/8YSZ TBCs?650 cycles?had a longer thermal cycling lifetime than SZ7C3/8YSZ?325 cycles?and LZ7C3/8YSZ?50 cycles?,the failures of these TBCs all occurred in the surface layer of RZ7C3 coating,which may be caused by the low fracture toughness and thermal expansion coefficient of RZ7C3 layer.However,GZ7C3/8YSZ has a longer thermal cycling lifetime attributed to its lower thermal conductivity and relatively high thermal expansion coefficient(9.90×10^-6K^-1).The CMAS resistance of the SZ7C3 and GZ7C3 ceramic material was studied.The results showed that SZ7C3 and GZ7C3 ceramic bulks reacted with CMAS rapidly to form a relatively dense reaction layer composed of apatite phase and fluorite phase,which prevented further infiltration of CMAS.It was also found that the smaller the rare earth ion radius,the faster the reaction with CMAS at high temperature,and the better the resistance to CMAS corrosion.Compared with LZ7C3and SZ7C3,GZ7C3 has better CMAS resistance because the Gd³⁺ion radius is smaller than that of La³⁺and Sm³⁺.In order to solve the blockage of the film holes in the blades during the preparation of the rare earth oxide TBC,the influence of cooling air flow on the preparation process and properties of TBC was studied in detail.8YSZ was first studied in this paper,the results showed that a certain amount of back cooling gas can improve the phenomenon of the film holes blockage and prolong the thermal cycling lifetime of the coating,which has made a great breakthrough in the application of TBC on turbine blade engines.It provides a solid foundation for the research on the blockage of air film holes with SZ7C3 and GZ7C3 new TBCS materials and the influence of cooling gas on coatings properties and thermal cycling lifetime.