Densification of ZrB2–TaSi2 and HfB2–TaSi2 Ultra‐High‐Temperature Ceramic Composites
Densification of ZrB2–TaSi2 and HfB2–TaSi2 Ultra‐High‐Temperature Ceramic Composites
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DOI：
10.1111/j.1551-2916.2010.04317.x
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发表时间：
2011-06
影响因子：
3.9
通讯作者：
L. Silvestroni;D. Sciti
中科院分区：
文献类型：
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作者：
L. Silvestroni;D. Sciti
采用x射线衍射、扫描电子显微镜（SEM）和透射电子显微镜（TEM）对含有15 vol% TaSi 2的全致密热压超高温陶瓷（UHTCs） ZrB 2和HfB 2的微观结构进行了表征。ZrB 2和HfB 2晶粒呈核-壳结构，核由原MB 2晶粒组成，壳由a (M, Ta) b2固溶体组成，在核上外延生长。低角度晶界和位错堆积调节了核壳之间的成分失配，特别是在ZrB 2基复合材料中，大量的Ta进入硼化物晶格。在三相点处检测到含有Zr或Hf杂质的ta5 Si 3、ta4.8 - si3c 0.3和ta5 sib2，并观察到Ta-Si- b -C- o非晶相对晶界的润湿作用。基于TEM、热力学计算和现有的相图，提出了ZrB 2和HfB 2添加TaSi 2后的致密化机理。本文所制备的UHTC复合材料的微观结构与添加相同量mosi2烧结的复合材料进行了比较。
The microstructure of fully dense hot-pressed ultra-high-temperature ceramics (UHTCs), namely ZrB 2 and HfB 2 containing 15 vol% of TaSi 2 , was characterized by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). ZrB 2 and HfB 2 grains displayed a core-shell structure: the core was constituted by the original MB 2 grain and the shell by a (M, Ta)B 2 solid solution, which grew epitaxially on the core. The compositional misfit between core-shell was accommodated by low-angle grain boundaries and dislocations pile-up, especially pronounced in the ZrB 2 -based composite, where a higher amount of Ta entered the boride lattice. Ta 5 Si 3 , Ta 4.8 -Si 3 C 0.3 , and Ta 5 SiB 2 , with Zr or Hf impurities, were detected at the triple points and wetting of the grain boundaries by a Ta-Si-B-C-O amorphous phase was observed. Based on the new microstructural features detected by TEM, thermodynamic calculations and the available phase diagrams, a densification mechanism for ZrB 2 and HfB 2 with addition of TaSi 2 is proposed. The microstructures of the UHTC composites presented here are compared with composites sintered with the addition of MoSi 2 in the same amount.