A highly dense and single phase (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2 ceramic product is obtained in this work at 1950°C (20 min, 20 MPa) by Spark Plasma Sintering (SPS) from powders prepared by Self-propagating High-temperature Synthesis (SHS). The formation of the (W,Mo)B2 secondary phase is avoided using fine W precursors and adding 1 wt% graphite to the SHS powders before SPS. Kinetic limitations responsible for hindering the synthesis of the high entropy boride are correspondingly eliminated. The resulting 98.5 % dense sample exhibits a homogeneous microstructure, with Vickers hardness of 26.8 GPa. The introduction of 20 vol% SiC produces an increase of the KIC values from 2.32 to 5.11 MPa m1/2. Very relevant is that the volatilization of Mo- and W-oxides occurring during sample oxidation at high temperature, which leads to its rapid degradation with the formation of a very porous oxide scale, can be strongly inhibited by the silicate phases generated in the composite ceramic.

中文翻译：

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超高温高熵 (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2 基陶瓷的加工和表征：W 粒度、石墨和 SiC 添加的影响


本工作采用自行制备的粉末，在 1950°C（20 分钟，20 MPa）下通过火花等离子烧结 (SPS) 获得高致密单相 (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2 陶瓷产品-传播高温合成（SHS）。使用细 W 前体并在 SPS 之前向 SHS 粉末中添加 1 wt% 石墨，可以避免 (W,Mo)B2 第二相的形成。相应地消除了阻碍高熵硼化物合成的动力学限制。所得密度为 98.5% 的样品具有均匀的微观结构，维氏硬度为 26.8 GPa。 20 vol% SiC 的引入使 KIC 值从 2.32 MPa m1/2 增加到 5.11 MPa m1/2。非常相关的是，样品高温氧化过程中发生的钼氧化物和钨氧化物的挥发，导致其快速降解并形成多孔氧化皮，复合陶瓷中生成的硅酸盐相可以强烈抑制钼氧化物和钨氧化物的挥发。 。