From individual to equimolar binary transition metal diborides: The case of (Nb0.5M0.5)B2, M=Ti, Hf

IF 6.2 2区材料科学 Q1 MATERIALS SCIENCE, CERAMICS Journal of The European Ceramic Society Pub Date : 2025-02-11 DOI:10.1016/j.jeurceramsoc.2025.117277

Luca Cappai , Mariano Casu , Antonio Mario Locci , Giacomo Cao , Sebastiano Garroni , Valeria Cannillo , Devis Bellucci , Roberto Orrù

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Abstract

(Nb_0.5Ti_0.5)B₂ and (Nb_0.5Hf_0.5)B₂ in bulk form were produced by Spark Plasma Sintering (SPS) from powders obtained by Self-propagating High-temperature Synthesis. The carbothermal reduction of oxide contaminants with graphite promoted the conversion of secondary phases into equimolar diborides, and improved samples densification, particularly for (Nb_0.5Hf_0.5)B₂ (from 89.7 % to 97.4 %). A single-phase solid solution was obtained for both systems at 2050 °C by SPS, while longer holding times (40 instead of 20 min) were needed for the Hf-containing ceramic. The latter system showed Vickers hardness (18.47 GPa) and Young’s modulus (586 GPa) slightly better than HfB₂. NbB₂ and (Nb_0.5Hf_0.5)B₂ were the most sensitive systems to the oxidation environment, with the formed oxide scales detached from samples at 600 and 800 °C, respectively, due to volume changes accompanying phase transitions in the generated niobium oxides. Conversely, the formation of a stable mixed oxide (TiNb₂O₇) made (Nb_0.5Ti_0.5)B₂ more resistant to oxidation, compared to TiB₂ and NbB₂.

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从单体到等摩尔二元过渡金属二硼化物：（Nb0.5M0.5）B2， M=Ti， Hf的情况

采用火花等离子烧结（SPS）法制备了（Nb0.5Ti0.5）B2和（Nb0.5Hf0.5）B2粉体。氧化污染物与石墨的碳热还原促进了二次相向等摩尔二硼化物的转化，并改善了样品的致密性，特别是（Nb0.5Hf0.5）B2（从89.7% %降至97.4% %）。在2050 °C的温度下，两种体系都获得了单相固溶体，而含hf陶瓷需要更长的保温时间（40分钟而不是20 分钟）。后者的维氏硬度（18.47 GPa）和杨氏模量（586 GPa）略优于HfB2。NbB2和（Nb0.5Hf0.5）B2是对氧化环境最敏感的体系，由于生成的铌氧化物伴随相变而发生体积变化，在600和800 °C时形成的氧化鳞分别从样品上脱落。相反，与TiB2和NbB2相比，形成稳定的混合氧化物（TiNb2O7）使（Nb0.5Ti0.5）B2具有更强的抗氧化性。

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来源期刊

Journal of The European Ceramic Society 工程技术-材料科学：硅酸盐

CiteScore

10.70

自引率

12.30%

发文量

863

审稿时长

35 days

期刊介绍： The Journal of the European Ceramic Society publishes the results of original research and reviews relating to ceramic materials. Papers of either an experimental or theoretical character will be welcomed on a fully international basis. The emphasis is on novel generic science concerning the relationships between processing, microstructure and properties of polycrystalline ceramics consolidated at high temperature. Papers may relate to any of the conventional categories of ceramic: structural, functional, traditional or composite. The central objective is to sustain a high standard of research quality by means of appropriate reviewing procedures.