Papers by Author: Xin Gui Zhou

Abstract: Nanographites supported by silicon carbide (SiC) nanoparticles were prepared through one-step pyrolysis method using polycarbosilane (PCS) as the precursor at temperatures ranging from 1100°C~1400°C. The effects of reaction temperature on the morphology, microstructure and crystallinity of the graphite flakes on SiC particles were explored by means of SEM, TEM, RAMAN and XRD. The experimental results show that the desired products with core/shell structures can only be obtained at reaction temperatures higher than 1100°C. With the increase of reaction temperature (1250°C~1400°C), the thickness and the average size of sp² domains show an incremental trend before a decline while the density and the degree of deformation continuously improve. The possible mechanism for those changes was also discussed.

Abstract: Continuous silicon carbide fiber reinforced silicon carbide matrix (SiCf/SiC) composites were fabricated by a combining polymer impregnation and pyrolysis (PIP) and vapor silicon infiltration (VSI) process. The mechanical properties and microstructure of the SiCf/SiC composites were studied. The results show that the open porosity of the SiCf/SiC composites is near zero. The density and mechanical properties of SiCf/SiC increase with decreasing the porosity of SiCf/C. However, the SiC fibers are damaged during the VSI process due to the reaction between SiC fibers and vapor Si.

Abstract: CNTs/AlN ceramics were fabricated by hot-pressing sintering process. The fracture toughness was measured by indentation method. The morphologies of indentation cracks were analyzed by SEM. The results show that the facture toughness of AlN was slightly improved because appreciate toughening mechanisms such as CNTs pull-out, crack bridging and deflect operate in CNTs/AlN. In addition, the facture toughness of CNTs/AlN increased with increasing CNTs content up to 3wt%. Then, the fracture toughness decrease when the CNTs content is 4wt%.

Abstract: CNTs/AlN ceramics were fabricated by hot-pressing and their bulk density, flexural strength, thermal conductivity were characterized. The microstructure was also investigated. The fracture surface were analyzed by SEM. TEM was used for analyzing the microstructure. It is found that the density, mechanic and thermal-conductivity properties markedly decreased as the CNTs reinforced AlN ceramic; through microstructure observation, the conglomeration of CNTs mostly exist among the AlN grain boundary, and the CNTs were scathed by the high temperature and pressure of the hot-pressing.

Abstract: The influence of the fiber/matrix interlayers on the mechanical properties of T800-HB fiber (a kind of carbon fiber) (the fibrous is three-dimensional four-directional braided) reinforced silicon carbide (SiC) matrix composites has been evaluated in this paper. The composites were fabricated through PIP process, and SiC layers were deposited as fiber/matrix interlayers by the isothermal CVD process. Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces. The mechanical properties were investigated using three-point bending test and single-edge notched beam test. The T800-HB/SiC composites exhibited high mechanical strength, and the flexural strength and fracture toughness were 511.5MPa and 20.8MPa•m1/2, respectively.

Abstract: A new technology, prefabricating pore media (PPM) technology that adopt glass fiber as pore media, for porous transpiration cooling C/SiC composites was studied. The result shows that the technology can control the pore structure successfully by the volume content and distribution of glass fiber in the braid, and the porous C/SiC composites have good bending strength above 300MPa.

Abstract: 3D braided carbon fiber reinforced silicon carbide (3D-Cf/SiC) composites were fabricated by precursor infiltration and pyrolysis(PIP), with carbon coatings prepared by chemical vapor deposition (CVD) before PIP. The effect of 1873K heat treatment on the mechanical properties of Cf/SiC composites were investigated. The results showed that heat treatment before PIP can increase the density of composites and lead to excellent properties of Cf/SiC composites. The flexual strength of the Cf/SiC composites with one cycle of 1873 K heat treatment reached 571 MPa, shear strength 51 MPa, and fracture toughness 18 MPa⋅m1/2.

Abstract: CF/SiC and Hi-Nicalon/SiC composites were prepared by precursor pyrolysis-hot pressing, and the microstructure and fracture behavior of the composites were investigated. Because of a strongly bonded fiber/matrix interface primarily resulting from the direct reactions between the fibers and matrix, Hi-Nicalon/SiC composite exhibited a typical brittle fracture behavior. However, CF/SiC composite displayed a tough fracture behavior with extensive fiber pullout, which was primarily attributed to a weakly bonded fiber/matrix interface as well as higher strength retention of the fibers. As a result, CF/SiC composite achieved better mechanical properties of 691.6 MPa in strength and 20.7 MPa•m1/2 in toughness, which were much higher than those of Hi-Nicalon/SiC composite.