高熵(Zr,Hf,Nb,Ta)C微米长方体的制备、吸波性能和抗氧化性研究

针对高熵碳化物制备困难，本文采用ZrC、HfC、NbC和TaC粉为原料，Ni粉为熔剂，通过低温无压烧结工艺成功制备出三种不同成分的高熵(Zr, Hf, Nb, Ta)C粉体。结果表明，三种粉体均为微米长方体，且暴露(100)晶面。(Zr_1/4Hf_1/4Nb_1/4Ta_1/4)C微米长方体因具有高介电常数而展现出优异的吸波性能，在厚度为3.5 mm、频率为6.16 GHz时，最低反射损耗值可达-48.86 dB。高熵(Zr, Hf, Nb, Ta)C微米长方体在800～1 200℃下展示出优异的抗氧化性，且氧化产物均由正交相(Nb_xTa_1-x)₂O₅固溶体、单斜相(Zr_xHf_1-x)O₂固溶体和正交相HfO₂所组成，与氧化温度和过渡金属的物质的量比无关。Zr、Hf、Nb和Ta的协同作用导致其氧化机制与单组元碳化物截然不同，Hf的存...

Preparation,Microwave Absorption Properties and Oxidation Resistance of High-Entropy (Zr,Hf,Nb,Ta)C Microcuboids

In response to the difficulty of the synthesis of high-entropy carbides (HECs), a pressureless low-temperature sintering strategy was utilized to prepare (Zr,Hf,Nb,Ta)C powders with three different transition metal proportion, which powder mixtures of ZrC, HfC, NbC, TaC and Ni were initially annealed at 1 500 ℃ under a flowing Ar atmosphere, and then etched by the nitric acid solution in order to dissolve the metal matrix. The results show that all samples exhibit cuboid morphology with an average size of 2 μm and the exposure of (100) face. Due to high dielectric constant, (Zr_1/4Hf_1/4Nb_1/4Ta_1/4)C microcuboids show good microwave absorption performance, and its minimum value of reflection loss attains -48.86 dB at a thickness of 3.5 mm and a frequency of 6.16 GHz. As-fabricated HECs samples also possess good oxidation resistance at 800~1 200 ℃. Moreover, oxidation products are irrelevant to the transition metal proportion and oxidation temperature, which are composed of orthorhombic Nb₂O₅-Ta₂O₅ solid solution (o-(Nb_xTa_1-x)₂O₅), monoclinic ZrO₂-HfO₂ solid solution (m-(Zr_xHf_1-x)O₂) and orthorhombic HfO₂(o-HfO₂). Notably, the synergy effect caused by transition metal elements significantly influences the phase transition process of oxides in comparison with monocarbide. In specific, the existence of Hf inhibits the transition of Nb₂O₅ from orthorhombic to monoclinic, in the meantime, assists the transition of ZrO₂ from tetragonal to monoclinic even at 800 ℃. Moreover, the addition of Nb and Ta accelerates the phase transition of HfO₂ from monoclinic to orthorhombic under atmospheric pressure.