Influence Of Hf Doping On The Stability And Mechanical Properties Of YTaO₄ Ceramic Phase

The thermal barrier coating is used as a high-temperature thermal protection coating to reduce the temperature of the hot end components of the aeroengine,thereby achieving the purpose of improving its life and efficiency.The inlet temperature of the front of the turbine is also greatly increased with the increase of the weight ratio of the aero engine.However,the currently used yttria-stabilized zirconia?7-8YSZ?,which is prone to undergo a phase change when it is put into service for a long time at 1200?,causing the coating to crack and eventually fail.Therefore,it has been unable to meet the development needs of aero engines.Based on this,this article studies the phase balance and composition and distribution of HfO₂-YO_1.5-Ta O_2.5 at1500?,and modifies YTa O₄ceramics with HfO₂ doping in order to obtain good phase stability and mechanical properties.The main research content and results are as follows:?1?A series of samples were prepared by chemical reverse co-precipitation.The phase balance,phase structure and microstructure of the material were systematically studied.Finally,the phase balance and distribution of HfO₂-YO_1.5-Ta O_2.5 at 1500?are given in the experiment.Studies have shown that the fluorite structural phase can be extended into the YO_1.5-Ta O_2.5 binary system at 1500?.In the vicinity of the rich Ta O_2.5component,the perovskite structure YTa₃O₉and the hexagonal system YTa₇O₁₉ can exist stably.In the phase diagram of HfO₂-YO_1.5-Ta O_2.5,the phase domain of pure phase YTa O₄ is relatively narrow.?2?Preparation of 5 mol% HfO₂,15 mol%HfO₂,20 mol%HfO₂,25 mol%HfO₂modified YTa O₄ ceramics by chemical co-precipitation method.The phase stability of the samples was characterized.And calculated the phase transition of YTa O₄ using DFT.Studies have shown that the initial monoclinic phase M'is a low-temperature thermodynamic phase.And doping HfO₂ into YTa O₄ improves the phase stability of the M'phase.At 1200°C,the solid solubility of M'relative to the fluorite structure HfO₂ is relatively large.At 1500°C,when the doping amount exceeds 15 mol%HfO₂,cubic HfO₂ precipitates in the second phase fluorite structure.?3?Nanoindentation and Vickers indentation techniques were used to characterize the Young's modulus,hardness and fracture toughness of HfO₂-doped YTa O₄ceramic blocks.According to the experiment,the Young's modulus range of M-YTa O₄ is 110.3?520.6 HV.The Young's modulus of M'-YTa O₄ranges from 77.4to 147.7 GPa,and the hardness ranges from 456.3 to 675.3 HV.Thus,the Young's modulus and hardness of M-YTa O₄are higher than that of M'-YTa O₄.As the doping amount of HfO₂ increases,the Young's modulus and hardness of the M'-YTa O₄ceramic block also increase.After adding HfO₂ to YTa O₄,the fracture toughness of the ceramic block has also been improved,ranging from 1.31 MPa·m^1/2 to 2.91MPa·m^1/2.