高熵陶瓷固溶结构的透射电镜研究

高熵会带来热力学上的高熵效应、结构上的晶格畸变效应、动力学上的迟滞扩散效应以及性能上的"鸡尾酒"效应,通过高熵设计来提高陶瓷材料的性能是目前研究的热点,而通过透射电镜揭示高熵结构及其与性能相关性的研究还很缺乏。本研究以相应金属氧化物、碳化硼和石墨为原材料,在制备高熵硼化物和高熵碳化物粉体的基础上,利用放电等离子体烧结制备得到高熵(TiZrHfNbTa)B₂和(TiZrHfNbTa)C陶瓷。采用透射电子显微镜及其能谱分析手段对两种高熵陶瓷进行了纳米尺度和原子尺度的结构表征,发现过渡金属元素固溶后保持了晶体结构的完整性,五种元素分布均匀,但在原子尺度存在固溶元素的浓度振荡、原子离散和晶格应变。本工作获得的原子尺度的固溶结构信息将有助于对高熵陶瓷构效关系的理解,并为高熵陶瓷的组分和结构设计提供实验依据。

Study on the Solid Solution Structures of High-entropy Ceramics by Transmission Electron Microscopy

High-entropy brings high-entropy effect on thermodynamics,lattice distortion effect on structure,diffusion retardation effect on dynamics and“cocktail”effect on properties in materials.It is a hotspot to improve the properties of ceramics by high-entropy design.However,it still lacks the study of high-entropy structures and their correlation to the properties through transmission electron microscopy(TEM).In this study,high-entropy borides and carbides powders were fabricated by using metal oxides,boron carbide and graphite as raw materials.The high-entropy(TiZrHfNbTa)B2 and(TiZrHfNbTa)C ceramics were then synthesized by spark plasma sintering of the as-fabricated powders.Transmission electron microscope and energy dispersive spectrometry were used to characterize the structure of the two high-entropy ceramics at the nano-scale and atomic-scale.The integrity of crystal structure maintained after solid solution of five transition metal elements which were found to uniformly distribute in the ceramics.However,at atomic scales,concentration oscillations of solid solution elements,atomic dispersion and lattice strain were observed.The solid solution structures at atomic scales as-obtained in this work can help to understand the structure-property relationship of high-entropy ceramics and provide experimental basis for the composition and structure design of high-entropy ceramics.