Research On Suspension Plasma Spraying And Thermal-mechanical Properties Of Zr₆Ta₂O₁₇ Ceramic

The exploration of high performance thermal barrier coating materials is an important research topic in the field of aviation industry.As a traditional thermal barrier coating material,YSZ has faced the bottleneck of temperature application.On the one hand,with the increase of combustion chamber temperature,molten external inhaled particles deposited on the surface of the coating,leading to CMAS corrosion,resulting in rapid failure of the coating.On the other hand,when the service temperature exceeds 1200℃,the irreversible phase transformation of YSZ from tetragonal phase to monoclinic phase will be occurred,which leads to the volume expansion of the coating and further increases the destructive stress,causes the premature spalling of the coating.The novel Zr₆Ta₂O₁₇ ceramics belong to A₆B₂O₁₇（A=Zr,Hf;B=Nb,Ta）crystal system.The ceramic has been proven to have low oxygen diffusivity,high melting point,thermal expansion coefficient matching with the alloy substrate,and not undergoing phase transformation up to its melting point.Therefore,it can be used as a candidate material for thermal barrier coatings.However,the thermal-mechanical properties of Zr₆Ta₂O₁₇ ceramics and the suspension plasma sprayed Zr₆Ta₂O₁₇coatings have hardly been reported.Based on these considerations,the main research results of this paper are as follows:1.Zr₆Ta₂O₁₇ ceramics were successfully prepared by in-situ solid-state method combined with pressureless sintering.The phase composition,microstructure,densification behavior,mechanical properties and CMAS corrosion resistance of Zr₆Ta₂O₁₇ ceramics at different sintering temperatures were studied.The thermal conductivity of Zr₆Ta₂O₁₇ ceramics was measured.The results show that all the ceramics possess a single orthonormal A₆B₂O₁₇ structure.With the increase of sintering temperature from 1400℃to 1500℃,the microstructure characterization shown that the density of Zr₆Ta₂O₁₇ ceramic increases from 62.6%to 98.3%,and reached the maximum value of 99.3%at 1600℃.2.Through Vickers indentation technology,the hardness and fracture toughness of ceramics sintered at 1500℃reached 15.8±0.93 GPa and 2.8±0.4 MPa·m^1/2,shown good mechanical properties.The mechanical properties of ceramics sintered at 1600℃decreased slightly due to abnormal grain growth.The thermal conductivity of Zr₆Ta₂O₁₇ ceramics from room temperature to 1000℃is lower than 1.7 W·m^-1·K^-1,which is better than that of YSZ materials.The corrosion products of the CMAS powder and Zr₆Ta₂O₁₇ powder mainly include ZrO₂,Zr SiO₄,Ca Ta₂O₆,etc.Tantalum oxide in Zr₆Ta₂O₁₇ would react with CMAS first,formed Ca Ta₂O₆ to effectively prevent the infiltration of molten CMAS in the direction of thickness.The ceramics with the highest density have the best corrosion resistance.3.In this paper,ZrO₂-Ta₂O₅ single-layer coating and 8YSZ/ZrO₂-Ta₂O₅double-layer coating were prepared by suspension plasma spraying.Zr₆Ta₂O₁₇ coating was synthesized by in-situ annealing.In this process,rich vertical cracks that could alleviate thermal mismatch were formed.After heat treatment at 1100℃,the phase structure and composition of the coating basically did not change with the heat treatment time,which proved that the good phase stability of the coating.The thermal cycle performance of double-layer YSZ/Zr₆Ta₂O₁₇ coating reached 800 cycles and that of single-layer Zr₆Ta₂O₁₇ coating was 500 cycles,indicated that the double-layer coating had better damage resistance.Through nano indentation mode,the hardness and Young’s modulus of Zr₆Ta₂O₁₇ coating reached the highest values of 15.49 GPa and 188.67 GPa at heat treatment time of 50 h.The plastic index and plastic deformation resistance of Zr₆Ta₂O₁₇ coating decreased after heat treatment for more than 50 h,and the erosion resistance property of the coating was weakened.