Papers by Keyword: SiC Whisker

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Authors: Su Qiu Jia, Jin Tong, Yun Hai Ma
Abstract: SiC whiskers were prepared through carbonthermal reduction in two steps. Firstly raw rice husks (RHs) were pyrolysed in a graphite vacuum furnace at 460°C for 2 hours and coked rice husks were pyrolysed at 1400°C in argon atmosphere. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) was employed to characterize the morphology and phase composition of SiC whiskers. The results show that the diameters of SiC whiskers range in 20-200 nm and their lengths are in the range from hundreds of microns to several millimeters. The whiskers are straight and slightly rough and consist of β-SiC crystals with bamboo-like structure. Vapor-solid (VS) mechanism plays a key role at the early stage of SiC formation and VLS mechanism and vapor phase mechanism of the whiskers are involved during the growth of SiC whiskers.
Authors: Fan Tao Meng, Shan Yi Du, Gui Shan Tian, Yu Min Zhang
Abstract: Silicon carbide is one of the best materials for satellite mirror and chemical vapor deposition (CVD) is an effective method of preparing SiC whiskers and films. In this paper, SiC whiskers or films were deposited on substrates of RB-SiC in an upright chemical vapor deposition furnace of Φ150mm × 450 mm with methyltrichloride silicane (MTS) as precursor gas and H2 as carrier gas under dilute gases of different H2/Ar ratio and different deposition temperature between 1050°C and 1150°C. The morphology and composition of the CVD-SiC grown on RB-SiC substrate were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. As a result, whisker-like, worm-like or ball-like SiC can be respectively obtained dependent on different deposition conditions such as H2/Ar ratio and deposition temperature, and the composition of the productions are determined as β-SiC by XRD. Furthermore, the deposition mechanisms of different morphologies of SiC are introduced.
Authors: Ji Yeon Park, S.M. Kang, Weon Ju Kim, Woo Seog Ryu
Abstract: To obtain a dense SiCf/SiC composite by the chemical vapor infiltration (CVI) process, whisker growing before matrix filling was applied, which is called the whisker growing assisted CVI process. The whisker growing and matrix filling processes were carried out using MTS (CH3SiCl3) and H2 as source and diluent gases, respectively. Tyranno-SATM was used as a reinforced substrate. Characterizations of SiC whisker grown during the in situ whisker growing process have been investigated. The weight gain rates with the matrix filling time and the density of composites was measured. The flexural strength with the thickness of the pyrolytic carbon (PyC) interlayers has been evaluated. b-SiC whiskers with many stacking faults were grown well in the Tyranno SATM fabrics. Tyranno-SA/SiC composite with a PyC interlayer thickness of 150 nm had a flexural strength of 610 MPa and the density of 2.71 g/cm3.
Authors: Jing Lu, Yan Hui Wang, Xi Peng Xu
Abstract: In SiC whisker reinforced Al matrix composite, the interface reaction significantly influences the property of the composite. Si films have been deposited on SiC whiskers by quasi atomic layer deposition from gaseous SiH4 to protect the whiskers from being eroded by Al matrix. The structure and morphology of the coating were characterized by X-ray diffraction and transmission electron microscope. The coating deposited on SiC whiskers is cubic phase polycrystalline silicon and this ultrathin Si film is even and continuous, completely covering every individual SiC whisker. The effect of the Si coating on improving the whisker/matrix interaction was also studied in this work. The interface layer, Si coating, could effectively protect the SiC whisker from erosion caused by Al matrix during the high temperature manufacturing process and improve the adhesion between the SiC whisker and the Al matrix.
Authors: Jun Feng Hu, Shi Jie Zhu, Wen Xue Wang, Yukiko Nakahara
Abstract: SiC whisker reinforced Si3N4 composite was used for studying crack healing behavior. Surface crack and straight-through crack were introduced on the tensile surface of specimens by Vickers hardness indenter and single edge pre-crack beam method. The cracked specimens were heat-treated at 1000 , 1100 , 1200 and 1300 for 1 hour in air. Bending strength was measured at room temperature by three point bending tests system. It was investigated that the best heat treatment temperature of Si3N4/SiC whisker composite is 1200 -1300 . The relationship between bending strength and logarithm of crack area was near linear and parabola in original and heat-treated specimens, respectively. Crack healing behavior was analyzed by oxidation filling model according to oxidation kinetics.
Authors: Wataru Nakao, Sang Kee Lee, Masahiro Yokouchi, Koji Takahashi, Kotoji Ando
Abstract: For improving fracture toughness as well as endowing with excellent self-crack-healing ability, mullite/SiC particles /SiC whiskers multi-composites were developed. Crack-healing ability and the mechanical properties of the specimens were investigated. Mullite/ 20 vol% SiC whiskers, mullite/ 25 vol% SiC whiskers and mullite/ 15 vol% SiC whiskers/ 10 vol% SiC particles composites can completely heal the pre-crack of 100 ım in surface length by heat-treatment at 1300 oC for 2 h in air. However, not completeness of the strength recovery was caused for mullite/ 15 vol% SiC whiskers composite by crack-healing. In spite of the same SiC content, the crack-healing ability of mullite/ 15 vol% SiC whiskers/ 10 vol% SiC particles composite is superior to that of mullite/ 25 vol% SiC whiskers composite. Admixing with SiC whisker was effective for improvement in fracture toughness. Additionally, the fracture toughness was not reduced by admixing with SiC particles.
Authors: Masato Ono, Wataru Nakao, Koji Takahashi, Kotoji Ando
Abstract: Mullite reinforced by SiC whiskers, Mullite(W), was developed with the aim of improving fracture toughness and to add crack-healing ability. For determining the threshold stress during crack-healing, a composite having a semi-elliptical surface crack of 100 μm was crack-healed at 1473 K for 8 h in air under elevated static and cyclic stresses and the bending strength at 1473 K of the crack-healed composite under stress were also investigated. Mullite(W) crack-healed under static stress below 100 MPa were never fractured during crack-healing and had the same bending strength as the specimens crack-healed under no-stress. Therefore, the threshold static stress during crack-healing of Mullite(W) has been determined to be 100 MPa. The threshold cyclic stress has also been determined to be 150 MPa. Considering that the crack growth is time-dependent, the threshold stress for all conditions during crack-healing of Mullite(W) has been concluded to be 100 MPa.
Authors: Da Zhen Wang, Pei Feng Feng
Abstract: The precision turning experiments of aluminium composites reinforced with SiC whisker reinforcements were done by polycrystalloid diamond (PCD) tools. The measure analysis of the machined surface was carried out with Atom Force Microscope (AFM) and Scan Electronic Microscope (SEM). The roughness values of the machined surface were measured by Talysurf-6. The results show that the orientation of reinforcements in the machined surface will directly affect the deformation mechanism of SiC whiskers, microstructures of the machined surface, and to determine the quality of the machined surface. In the five types from A to E of SiC whisker orientation, the orientation of case A easily makes to produce SiC whisker deformation by cutting off directly, and to result in the best machined surface. However, for the orientation of case E, it easily makes to induce SiC whisker deformation by pulling out or pressing into aluminium matrix, and to produce the worst machined surface.
Authors: Sang Yeup Park, Hee Gon Bang
Abstract: Alumina/Alumina: SiC laminate composites were fabricated by the pressureless sintering method. Although the laminate defect, such as channel crack, was observed under the sintering of oxidation atmosphere, laminate defects were eliminated by the sintering of non-oxidation atmospheres. Among various atmospheres, the vacuum atmosphere was effective in the elimination of laminate defects and also for homogeneous microstructure.
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