氧化镱掺杂氧化铪陶瓷的高温相稳定性与热膨胀性能

Investigation of phase structure stability and thermal expansion coefficient of ytterbia stabilized hafnia

燃气涡轮发动机推重比的提高依赖于发动机工作温度的提升。目前,寻找比传统YSZ(氧化钇部分稳定的氧化锆)材料耐受温度更高,与镍基基体热膨胀系数匹配的新型热障涂层陶瓷材料是首要任务。采用水热法合成一系列氧化镱掺杂氧化铪(YbSH)纳米粉体,并通过固相烧结制备出YbSH陶瓷,分析了YbSH粉体与陶瓷的微观结构变化规律与相稳定机制,测试立方相结构YbSH陶瓷的高温相结构稳定性与热膨胀系数。利用X射线衍射(XRD)、拉曼光谱(Raman)和透射电子显微镜(TEM)分析Yb_(2)O_(3)掺杂HfO_(2)粉体与陶瓷的微观结构变化规律与相稳定机制;并借助热重-差热分析仪(DSC-TG)、热膨胀分析仪(TMA)测试立方相结构YbSH陶瓷的高温相结构稳定性与热膨胀系数。结果表明,水热合成粉体的粒径在10 nm以下,分布均一,多数呈正方体形状,结晶状态好,制备的烧结陶瓷致密度可达95%以上;晶体学分析得出,Yb(Ⅲ)离子通过取代Hf(Ⅳ)离子的位置,使氧化铪发生晶格畸变,以置换固溶的方式使HfO2的空间群从单斜相的P21/c畸变到萤石立方相Fm3m。氧化镱掺杂量的增多使氧化铪逐渐失去单斜相结构,12 mol/mol以上的氧化镱的掺杂可使氧化铪成为完全立方相,通过使阳离子网络的膨胀和氧空位的产生,有效缓解氧过度拥挤的情况,使立方萤石结构的HfO2稳定在室温下。通过高温热处理和监测升温过程中YbSH的热量变化,该立方相结构在室温至1500℃表现出良好的稳定性;YbSH陶瓷热膨胀系数随着立方相含量的增多从6.016×10^(-6)℃^(-1)增大至10.14×10^(-6)℃^(-1)(25~1500℃),其中20 mol/mol氧化镱掺杂的YbSH陶瓷的热膨胀系数可达10.5×10^(-6)℃^(-1)(1000~1200℃),比纯氧化铪热膨胀系数提高67.22%。

Improvement of the thrust weight ratio of gas turbine engine rely on increased engine operating temperature.At present,it is a priority to find new thermal barrier coating ceramic materials with a higher temperature tolerance than the traditional YSZ(Yttria partially stabilized zirconia)material and match thermal expansion coefficient of Ni-based superalloy matrix.A series of ytterbia stabilized hafnia(YbSH)were prepared with hydrothermal nano-powders by solid-state sintering.Effects of the ytterbia on the microstructure,phase stability,and thermal expansion coefficient of the doped hafnia ceramics were investigated.The microstructure and phase stability mechanism of Yb_(2)O_(3)-doped HfO_(2) powders and ceramics were analyzed by XRD,Raman,and TEM.DSC-TG and TMA were used to test the high temperature phase structure stability and thermal expansion coefficient of cubic phase structure of YbSH ceramics.The results showed that the grain size of the hydrothermal nano-powder was less than 10 nm,with a uniform distribution and a great crystal state.Most of the powers were cuboid and the density of the sintered ceramics can reach more than 95%.Crystallography analysis revealed that the Yb(III)ion distorted the lattice by replacing Hf(IV)ion position which made the space group of HfO2 from monoclinic phase distortion of P21/c to the cubic phase Fmˉ3m.The hafnia gradually lost its monoclinic phase structure with increasing doping amount of ytterbia,once the doping concentration of ytterbia raised up to 12 mol/mol.By expanding cationic network and generating oxygen vacancy,oxygen overcrowding was effectively alleviated.The cubic phase structure showed good stability from room temperature to 1500℃by high temperature heat treatment and monitoring enthalpy change of YbSH nanopowders and ceramics during heating process.Average thermal expansion coefficients of YbSH ceramics increased with cubic phase content increasing from 6.016×10^(-6)℃^(-1) to 10.14×10^(-6)℃^(-1)(from room temperature to 1500℃).The thermal expansion coefficient of YbSH ceramics doped with 20 mol/mol ytterbia can reach 10.5×10^(-6)℃^(-1)(from 1000℃to 1200℃),which was 67.22%higher than that of pure hafnia.