Abstract
Equimolar quinary diboride powders, with nominal composition of (Ti0.2Hf0.2Zr0.2Nb0.2Ta0.2)B2, were synthesized by boro/carbothermal reduction (BCTR) of oxide mixtures (MOx, M = Ti, Hf, Zr, Nb and Ta) using B4C as source of B and C in vacuum. By adjusting the B4C/MOx ratios, diboride mixtures without detectable MO, were obtained at 1600°C, while high-entropy diboride (HEB) powders with particle size of < 1 µm was obtained at 1800°C. The phase, morphology and solid solution evolution process of the HEB powders during the BCTR process were comprehensively investigated. Although X-ray diffraction pattern indicated the powders synthesized at 1800°C were in a single-phase AlB2 structure, elemental mappings showed that (Ta, Ti)-rich and (Zr, Nb)-rich solid solution coexisted in the HEB powders. The distribution of niobium and zirconium atoms in HEB was unable to reach uniform until the HEB powders were spark plasma sintered at 2000°C. (Ti0.2Hf0.2Zr0.2Nb0.2Ta0.2)B2 ceramics with a relative density of 97.9% were obtained after spark plasma sintering the HEB powders at 2050°C under 50 MPa. Rapid grain growth was found in this composition when the sintering temperature was increased from 2000 to 2050°C, and the averaged grain size increased from 6.67 to 41.2 µm. HEB ceramics sintered at 2000°C had a Vickers hardness of 22.44 ± 0.56 GPa (under a load of 1 kg), a Young’s modulus of ∼500 GPa and a fracture toughness of 2.83 ± 0.15 MPa m1/2. This is the first report for obtaining high density HEB ceramics without residual oxide phase, benefiting from the high quality HEB powders obtained.
摘要
以过渡金属氧化物(MOx)和碳化硼(B4C)为原料, 采用硼热/碳热还原技术在1800°C下制备得到了等摩尔比的亚微米级五元高熵硼化物(Ti0.2Hf0.2Zr0.2Nb0.2Ta0.2)B2粉体, 并深入探讨了硼热/碳热还原过程中产物的物相、形貌以及固溶体变化过程. X射线衍射谱表明所制备的粉体在1800°C即形成了单相结构, 但直到2000°C样品中各元素才分布均匀. 将得到的粉体在2050°C/50 MPa的条件下进行放电等离子烧结, 获得了相对密度为97.9%的高熵硼化物陶瓷. 研究发现, 当烧结温度从2000°C增加到2050°C时, 高熵陶瓷晶粒迅速长大, 平均晶粒尺寸从6.67 μm增大到41.2 μm. 2000°C下制备得到的高熵硼化物陶瓷具有良好的力学性能, 其硬度、杨氏模量和断裂韧性分别为22.44 ± 0.56 GPa, ∼500 GPa, 2.83 ± 0.15 MPa m1/2.
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (51521001 and 51832003), and the Fundamental Research Funds for the Central Universities.
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Author contributions Zou J and Fu ZY designed the research. Gu J and Zou J performed the experiments with the help of Wang H, Wang W, Zhang J and Fu ZY. Sun SK performed the XRD refinement. Yu SY and Zou J performed the hardness test. Fu Z supervised and acquired funding for the research. Gu J and Zou J wrote the paper. All authors discussed the results and commented on the manuscript.
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Junfeng Gu is currently a PhD student at the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology. His research focuses on the sintering mechanisms and properties of ultra-high temperature ceramics
Ji Zou is a Research Fellow at the University of Birmingham, UK and an adjunct professor at Wuhan Institute of Technology, China. He received his PhD degree from Shanghai Institute of Ceramics, Chinese Academy of Sciences. He has been active in the processing-structure-property correlation of ceramics, especially for boride ceramics
Zhengyi Fu is a chief professor at the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology. He received his PhD degree from Wuhan University of Technology in 1994. His current research interests include advanced sintering and bioprocess-inspired fabrication
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Dense and pure high-entropy metal diboride ceramics sintered from self-synthesized powders via boro/carbothermal reduction approach
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Gu, J., Zou, J., Sun, SK. et al. Dense and pure high-entropy metal diboride ceramics sintered from self-synthesized powders via boro/carbothermal reduction approach. Sci. China Mater. 62, 1898–1909 (2019). https://doi.org/10.1007/s40843-019-9469-4
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DOI: https://doi.org/10.1007/s40843-019-9469-4