Abstract
For the first time, a group of CaB6-typed cubic rare earth high-entropy hexaborides have been successfully fabricated into dense bulk pellets (>98.5 % in relative densities). The specimens are prepared from elemental precursors via in-situ metal-boron reactive spark plasma sintering. The sintered bulk pellets are determined to be single-phase without any detectable oxides or other secondary phases. The homogenous elemental distributions have been confirmed at both microscale and nanoscale. The Vickers microhardness are measured to be 16−18 GPa at a standard indentation load of 9.8 N. The nanoindentation hardness and Young’s moduli have been measured to be 19−22 GPa and 190−250 GPa, respectively, by nanoindentation test using a maximum load of 500 mN. The material work functions are determined to be 3.7–4.0 eV by ultraviolet photoelectron spectroscopy characterizations, which are significantly higher than that of LaB6.
Highlights
In 2004, Yeh et al [1] and Cantor et al [2] published two independent reports on the fabrication of high-entropy alloys (HEAs) or multi-principal element alloys
HEAs usually refer to metallic alloys with five or more elements of equimolar compositions, which can be considered as a subclass of complex concentrated alloys (CCAs) [3]
The powders were first mixed by a vortex mixer, and successively high energy ball milled (HEBM) in a SPEX 8000D mill (SPEX CertiPrep, NJ, USA)
Summary
In 2004, Yeh et al [1] and Cantor et al [2] published two independent reports on the fabrication of high-entropy alloys (HEAs) or multi-principal element alloys. HEAs usually refer to metallic alloys with five or more elements of equimolar (or near equimolar) compositions, which can be considered as a subclass of complex concentrated (or compositionally complex) alloys (CCAs) [3]. Similar to HEAs and CCAs, it was recently proposed to generalize HECs to compositionally complex ceramics (CCCs), where medium-entropy or non-equimolar compositions sometimes possess better properties [10, 27, 29, 30]
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