Haijun Zhou

Preparation and Property of SiC/(ZrB 2 -SiC/SiC) 4 Anti-oxidation Coatings for C f /SiC Composites: Preparation and Property of SiC/(ZrB 2 -SiC/SiC) 4 Anti-oxidation Coatings for C f /SiC Composites

以Cf/SiC复合材料为基体,采用浆料浸涂法和脉冲CVD法制备了SiC/（ZrB2-SiC/SiC）4涂层,借助XRD、扫描电镜及能谱对涂层的结构及组成进行了分析研究,并初步考查了其高温抗氧化性能.结果表明,涂层总厚度约100μm,主要由ZrB2-SiC涂层与脉冲CVD SiC涂层交替覆盖而成.在1500℃空气中氧化25h,未涂层试样失重明显; 脉冲CVD SiC涂层试样氧化失重率为5.1%; 而SiC/（ZrB2-SiC/SiC）4涂层试样出现增重现象,增重率达2.5%,表现出优异的抗氧化性能.

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。

Study on the In Situ Growth of Carbon Nanotubes for the Reinforcement of Cf/SiC Composite Fabricated by CVI+PIP Process

Cf/SiC composites were fabricated through in situ growth of carbon nanotubes (CNTs) on three-dimensional needle-punched carbon fabric via chemical vapor deposition and polymer impregnation and pyrolysis process. The mechanical and thermal properties of the composites were investigated. The flexural strength and fracture toughness were decreased due to the fiber volume fraction loss and much shorter pull-out length of fibers which was caused by the higher interfacial bonding strength between fiber and matrix after the growth of CNTs. Brittle fracture character of CNTs was observed due to the strong interfacial bonding strength between CNTs and matrix. The parallel thermal conductivity and perpendicular thermal conductivity were improved to 14.5% and 8.0% respectively.

Fabrication of ZrC-SiC Powders by Means of Liquid Precursor Conversion Method Using ZrC Precursor and Polycarbosilane

ZrC-SiC powders were fabricated by means of liquid precursor conversion method, using Zr containing polymer precursor and polycarbosilane. The effects of staring reagents and the pyrolysis temperature on the fabrication of ZrC-SiC powders were studied. Results show that ZrC-SiC powders with different ZrC/SiC ratio could be formed when the staring reagents were different. Pyrolysis temperature affects the pyrolysed product. When temperature was lower, less amount of ZrC was formed in the powder. The size of crystallite and morphology of the synthesized powders were characterized by transmission electron microscopy and scanning electron microscopy.

Oxidation behavior of Al2O3 added reaction-sintered SiC ceramics in wet oxygen environment at 1300°C

ABSTRACT The oxidation behavior of reaction-bonded SiC ceramics with Al2O3 was investigated at 1300°C for exposure duration up to 100 h under water vapor environment. Results show that Al2O3 is enriched on the oxidation surface, reducing the volatilization of the oxide layer and preventing the reduction of macroscopic size. Raman spectra results further testified that Al2O3 obviously improves the stability of glass structure and reduces the generation of non-bridged oxygen atoms (Si–O–H), which results in a lower reaction activity with steam of the aluminosilicate melt, therefore, significantly improving the oxidation resistance of SiC in O2/H2O atmosphere.

Fabrication and microstructure of ZrB2–ZrC–SiC coatings on C/C composites by reactive melt infiltration using ZrSi2 alloy

ZrB2–ZrC–SiC ternary coatings on C/C composites are investigated by reactive melt infiltration of ZrSi2 alloy into pre-coatings. Two different pre-coating structures, including porous B4C–C and dense C/B, are designed by slurry dip and chemical vapor deposition (CVD) process respectively. The coating prepared by reactive melt infiltration (RMI) into B4C–C presents a flat and smooth surface with a three-layer cross-sectional structure, namely interior SiC transition layer, gradient ZrB2–ZrC–SiC layer, and ZrB2–ZrC exterior layer. In comparison, the coating prepared by RMI into C/B shows a more granular surface with a different three-layer cross-sectional structure, interior unreacted B–C pre-coating layer, middle SiC layer, and exterior ZrB2–ZrC–ZrSi2 layer. The forming mechanisms of the specific microstructures in two coatings are also investigated and discussed in detail.

3D C f /SiBCN composites prepared by an improved polymer infiltration and pyrolysis

Using liquid poly(methylvinyl)borosilazanes (PMVBSZ) as precursor, carbon fiber reinforced SiBCN matrix composites (Cf/SiBCN) were fabricated by a modified polymer infiltration and pyrolysis (PIP) process. With dicumyl peroxide added as cross-linking agent, the PMVBSZ could be solidified at a low temperature of 120 °C, leading to a high ceramic yield of ~70%. The cross-linking mechanism and ceramization processes of the precursor were investigated in detail. Moreover, a modified infiltration technology was developed, which improved the efficiency and protected the precursor against moist air during PIP. Consequently, the obtained Cf/SiBCN composites had an oxygen content of around 1.22 wt%. Benefiting from the high ceramic yield and high efficiency of the modified PIP, Cf/SiBCN composites with an open porosity of ~10% and uniform microstructure were obtained after only 7 cycles of PIP. The flexural strength and fracture toughness of the derived Cf/SiBCN composites were 371 MPa and 12.9 MPa·m1/2, respectively. This work provides a potential route for the fabrication of high performance Cf/SiBCN composites.

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。

Mechanical and Tribological Properties of 3D Carbon Fiber Reinforced SiC Composites Prepared by Liquid Silicon Infiltration

C/SiC composites were prepared by liquid silicon infiltration process, and their microstructure, mechanical and tribological properties were studied in this paper. The results showed that the composites demonstrated non-catastrophic fracture behavior with long fibers pulled out and about 115 MPa flexural strength. The stability of coefficient of friction (COF) was improved and wear rate demonstrated a linear variation with the increasing of rotation speeds. However, wear rate exhibited a higher value (~3.6 μg/m) under a higher load (~150 N), even though the COF curves for C/SiC composites showed no significant changes.