Le Gao

In situ growth behavior of boron nitride nanotubes on the surface of silicon carbide fibers as hierarchical reinforcements

BNNTs grown in situ on the surface of silicon carbide fibers via a simplified ball milling, impregnation and annealing method using boron powder as the raw material were synthesized. The morphology, microstructure and chemical composition of as-grown BNNTs were well characterized by field-emission scanning electron microscopy, field emission transmission electron microscopy, electron energy loss spectroscopy and Raman spectroscopy. The analysis results indicate that the nanostructures are BNNTs with the diameter of 50–130 nm, exhibiting a multi-walled and bamboo-like structure and possessing two distinct morphologies of the tube walls: flat walls and bubble-chain walls, respectively. Based on the experimental characterization of BNNTs and as-milled powders, the possible growth process of BNNTs has been described and the formation mechanisms of two types of bamboo-like BNNTs have been proposed, including the tip growth mode and the base growth mode.

Ablation Properties of ZrB 2 -SiC Ultra-high Temperature Ceramic Coatings: Ablation Properties of ZrB 2 -SiC Ultra-high Temperature Ceramic Coatings

为了提高C/C复合材料的抗氧化烧蚀性能, 采用浆料浸涂与原位反应复合工艺在材料表面制备了ZrB 2 -SiC超高温陶瓷涂层, 利用氧-丙烷火焰测试了涂层的抗烧蚀性能。结果表明: 采用复合工艺所制备的ZrB 2 -SiC超高温陶瓷涂层与基材具有较高的结合强度; 在氧-丙烷火焰冲刷条件下, 涂层具有良好的抗烧蚀性能, 涂层经1500℃下烧蚀600 s, ZrB 2 -SiC涂层无明显烧蚀, C/C复合材料保持完好。微观结构观察表明: 烧蚀测试后, 涂层中存在ZrO 2 和大量超高温陶瓷相, 涂层抗烧蚀形式主要表现为热化学烧蚀和机械剥蚀。为了提高C/C复合材料的抗氧化烧蚀性能, 采用浆料浸涂与原位反应复合工艺在材料表面制备了ZrB 2 -SiC超高温陶瓷涂层, 利用氧-丙烷火焰测试了涂层的抗烧蚀性能。结果表明: 采用复合工艺所制备的ZrB 2 -SiC超高温陶瓷涂层与基材具有较高的结合强度; 在氧-丙烷火焰冲刷条件下, 涂层具有良好的抗烧蚀性能, 涂层经1500℃下烧蚀600 s, ZrB 2 -SiC涂层无明显烧蚀, C/C复合材料保持完好。微观结构观察表明: 烧蚀测试后, 涂层中存在ZrO 2 和大量超高温陶瓷相, 涂层抗烧蚀形式主要表现为热化学烧蚀和机械剥蚀。

ZrB2-SiC Coatings Prepared by Vapor and Liquid Silicon Infiltration Methods: Microstructure and Oxidation Resistance Property: ZrB2-SiC Coatings Prepared by Vapor and Liquid Silicon Infiltration Methods: Microstructure and Oxidation Resistance Property

Novel zirconium diboride-silicon carbide (ZrB2-SiC) coatings were prepared by vapor silicon infiltration (VSI) and liquid silicon infiltration (LSI), respectively. The static oxidation resistance properties of these coatings were evaluated and their microstructure evolution during oxidation was studied. It showed that the VSI coating had better oxidation resistance than LSI. A compact oxide scale was formed on the VSI coating, which strongly suppressed fur- ther oxidation damage during the testing. The poor oxidation resistance of the LSI coating could be mainly attributed to micro-cracks and residual silicon.为了提高陶瓷基复合材料的抗氧化性能，分别采用气相、液相渗硅工艺制备了ZrB 2 -SiC涂层，利用静态氧化试验测试了ZrB 2 -SiC涂层的抗氧化性能，并分析了涂层的微观结构演化过程。结果表明：气相渗硅工艺制备的涂层抗氧化性能更优良，氧化试验后在涂层表面形成一层致密结构的氧化物层，有效抑制氧化性气体向涂层内部扩散，提高涂层的高温抗氧化防护能力。由于液相渗硅工艺制备的涂层存在残留硅成分和微裂纹，导致涂层高温抗氧化防护能力较差。为了提高陶瓷基复合材料的抗氧化性能，分别采用气相、液相渗硅工艺制备了ZrB 2 -SiC涂层，利用静态氧化试验测试了ZrB 2 -SiC涂层的抗氧化性能，并分析了涂层的微观结构演化过程。结果表明：气相渗硅工艺制备的涂层抗氧化性能更优良，氧化试验后在涂层表面形成一层致密结构的氧化物层，有效抑制氧化性气体向涂层内部扩散，提高涂层的高温抗氧化防护能力。由于液相渗硅工艺制备的涂层存在残留硅成分和微裂纹，导致涂层高温抗氧化防护能力较差。