Progress in the fabrication of ultra-high-temperature ceramics: “in situ” synthesis, microstructure and properties of a reactive hot-pressed HfB₂–SiC composite

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• 作者：Fré ; dé ; ric Monteverde
• 关键词：Ultra-high temperature ceramic (UHTCs) ; Microstructure ; Thermomechanical properties ; Oxidation ; Reactive hot-pressing
• 刊名：Composites Science and Technology
• 出版年：2005
• 期刊代码：19_02663538
• 类别：ms
• 出版时间：2005
• 卷：65
• 期：11-12
• 页码：1869-1879
• 文件大小：447 K

摘要

An ultra-high-temperature HfB₂–SiC composite was successfully fabricated by reactive hot-pressing. Solid reagents like Hf/Si/B₄C, mechanically mixed in molar ratio 2.2/0.8/1, were “in situ” converted into the basic ingredients (i.e., HfB₂, SiC), and then directly hot-pressed until full density was achieved (1900 °C final temperature). The microstructure consisted of faceted diboride grains (mean size 3 μm), with HfC (6 vol%) and SiC (22 vol%and mean size 1 μm) evenly distributed intergranularly. The combination of some mechanical properties was of considerable significance: about 19 GPa of micro-hardness, 520 GPa of Young’s modulus, 770 ± 35 and 315 ± 10 MPa of flexural strength at 25 and 1500 °C, respectively. A relevant merit characterized the resistance to oxidation: repeated exposures at 1700 °C, or at 1450 °C for 20 h, involved limited mass gains and small changes of the original microstructure. The marked refractoriness of HfB₂ and SiC, which constitute the framework of the composite, dominates beneficially its thermostructural stability.