Effect of Nb content on the phase composition, densification, microstructure, and mechanical properties of high-entropy boride ceramics
Effect of Nb content on the phase composition, densification, microstructure, and mechanical properties of high-entropy boride ceramics
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DOI：
10.1016/j.jeurceramsoc.2020.08.058
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发表时间：
2021-01-01
影响因子：
5.7
通讯作者：
Monteverde, Frederic
中科院分区：
文献类型：
--
作者：
Feng, Lun;Fahrenholtz, William G.;Monteverde, Frederic
采用两步放电等离子烧结法制备了Nb含量为0~20at%的致密高熵(Hf、Zr、Ti、Ta、Nb)B-2陶瓷。X-射线衍射分析表明，在不含Nb的成分中发现了单相的六方结构。相反，在含Nb的成分中，存在两个相同的六方结构的相，但点阵参数略有不同。Nb的加入导致了富Nb的第二相的存在，并且第二相的数量随着Nb含量的增加而增加。当Nb含量从0增加到20at%时，相对密度从接近100%下降到接近99.5%。平均晶粒度由未加Nb时的13.9+/-5.5 mm降至Nb含量为20at%时的5.2+/-2.0 mm。随着Nb含量的增加，晶粒尺寸减小的原因是富Nb的第二相抑制了晶粒长大。Nb的加入提高了复合材料的杨氏弹性模量和维氏硬度，但降低了剪切弹性模量。当部分Nb溶解到主相中时，在所有含Nb的成分中都形成了富Nb的第二相。
Dense high-entropy (Hf,Zr,Ti,Ta,Nb)B-2 ceramics with Nb contents ranging from 0 to 20 at% were produced by a two-step spark plasma sintering process. X-ray diffraction indicated that a single-phase with hexagonal structure was detected in the composition without Nb. In contrast, two phases with the same hexagonal structure, but slightly different lattice parameters were present in compositions containing Nb. The addition of Nb resulted in the presence of a Nb-rich second phase and the amount of the second phase increased as the Nb content increased. The relative densities were all >99.5 %, but decreased from similar to 100 % to similar to 99.5 % as the Nb content increased from 0 to 20 at%. The average grain size decreased from 13.9 +/- 5.5 mu m for the composition without Nb additions to 5.2 +/- 2.0 mu m for the composition containing 20 at% Nb. The reduction of grain size with increasing Nb content was due to the suppression of grain growth by the Nb-rich second phase. The addition of Nb increased Young's modulus and Vickers hardness, but decreased shear modulus. While some Nb dissolved into the main phase, a Nb-rich second phase was formed in all Nb-containing compositions.