Papers by Author: Zhao Hui Chen

Abstract: Carbon fiber reinforced silicon carbide composites (C_f/SiC) were derived through precursor infiltration pyrolysis route (PIP) at 1600°C in vacuum atmosphere using polysiloxane as precursor. The matrix of C_f/SiC was characterized by X-ray diffraction and elemental analysis. The results show that crystalline β-SiC can be derived at 1600°C in vacuum from polysiloxane. The flexural strength and fracture toughness of polysiloxane derived from C_f/SiC can reach up to 70 MPa and 2.3MPa·m respectively^1/2.

Abstract: ZrC-Zr2Si coating was prepared on carbon fiber reinforced silicon carbide matrix composites (C/SiC) by pack cementation method to prevent these composites from oxidation. SEM, EDS and XRD were applied to analyze the surface and cross-section morphologies, element distribution and phase composition of the coating, respectively. The results show that the coating made by the technique exhibits excellent oxidation resistance. The optimizing infiltration composition and process was: 60wt.%Zr-Si, 30wt.%PCS-DVB, 10wt.%Al2O3, holding 8 hours at 1400°C in Ar protecting atmosphere, ZrC-Zr2Si coating is obtained, homogeneous and density. The weight loss percentage of the coated C/SiC is only 1.52％after oxidation in air at 1500°Cfor 30min.

Abstract: Polycarbosilane (PCS) was introduced into preforms to prepare W-ZrC cermets by reactive melt infiltration (RMI). Properties and microstructure of the preforms and cermets were analyzed with XRD, SEM and EDS. The preforms had an open porosity of 42.0 %, and the WC particles were cemented by the pyrolysate of PCS. W-ZrC cermets were prepared by heating Zr2Cu covered preforms to 1300 °C for 3 h. XRD revealed that the resulting cermets were made up of W, ZrC and W2C. The cermets had an open porosity of 3.5 %, a flexural strength of 354.0 MPa, a flexural modulus of 192.5 GPa and a flexural toughness of 5.72 MPa·m1/2 .

Abstract: Partially sintered zirconia ceramics (PSZCs) for dental uses were prepared from zirconia nanopowder via isostatic pressing and partially sintering. The open porosities, pore diameters, grain sizes and mechanical properties of the ceramics with different densities were studied. The results show that the pores formed in the PSZCs are all open pores, with a diameter distribution of 60nm~130nm and a grain size distribution of 120~170nm. The machinability becomes worse when the density of PSZC is higher than 75% of the theoretical density, so a ceramic named PSZC-70% with density of 70%TD was selected as the target material. Its bending strength is 168 MPa and fracture toughness is 1.8 MPa·m1/2. A dental restoration framework can be obtained via machining the PSZC-70% on a dental CAD/CAM system.

Abstract: In this paper a pseudo-HP process, which uses solid powder to transfer pressure to prepare complex shape articles, was adopted to prepare 2D C/SiC composites. Nano-SiC powder was used to lower the sintering temperature, thus decreasing the damage to carbon fibers. The optimum processing parameters are as follows: sintering temperature 1850°C, holding time 60min, sintering pressure 10MPa. The maximum strength is over 300MPa, and toughness is around 8MPa·m1/2. BN powder is more lubricous than carbon powder, and thus is more convenient for demoulding and pressure transferring. Precursor Infiltration and Pyrolysis (PIP) was used to further densify the composites after HP process, and strength and toughness of the samples were slightly enhanced.

Abstract: The microstructure and its evolution of 3D-Cf/SiC composites derived from organic precursor are studied by using scanning electronic microscopy, mercury intrusion porosimetry, isothermal N2 sorption and bubble point method, etc. As the results shown, MIP is preferable to N2 sorption for the characterization of pore size distribution (PSD) because of its wider effective probing ranges. The typical porosity of fabricated 3D-Cf/SiC composites is 10-15vol.%, and all the pores distribute in a quite wide size ranging from some dozens of nanometers to hundreds of microns and can be divided into three groups, according to their sizes, contents and locations: the inter-bundle macro-pores/paths, the intra-bundle pores and the micro-pores/cracks around the interfaces or in the matrixes. The macro-pores/paths constitute a porous network, which is partially open throughout the composites.

Abstract: A novel composite, 3D C/SiC-Cu, which contained copper as transpiration agent, was designed and prepared. The influence of copper contents (2.18, 4.86, 6.53vol %) upon the mechanical and anti-ablative properties was investigated. The flexural strengths of three composites were over 450MPa, and fracture toughness over 15.0MPa•m1/2. After being ablated for 35 seconds in flowing oxyacetylene torch environment, the composites remained integral, and the flexural strength and strength retention ratio of the composite increased with the copper content increase. The maximum recession rate of the samples in oxyacetylene torch test was as low as 0.0490mm/s.

Abstract: Carbon fiber cloth reinforced silicon carbide (2D-Cf/SiC) composites were prepared through polycarbosilane(PCS) /divinylbenzene(DVB) pyrolysis with SiC as inactive filler. Effects of the molding pressure on the microstructure and mechanical properties of 2D-Cf/SiC composites were investigated. With increasing molding pressure from 0MPa to 3MPa, the fiber volume fraction of the composites was increased. As a result, the strengths of the composites were enhanced. But when the molding pressure exceeded 3MPa, SiC particles would damage the carbon fibers seriously. Therefore, although the fiber fraction of the composites was increased further, the flexural strengths of the composites were decreased. It was found that the composites fabricated with the molding pressure of 3 MPa exhibited highest flexural strength, reached 319.4 MPa.

Abstract: Two-dimensional carbon fiber cloth reinforced silicon oxycarbide (2D-Cf/Si-O-C) composites were fabricated with silicone resin (SR) as precursors, ethanol as solvent and SiC as inert fillers by precursor infiltration pyrolysis (PIP). Effects of the pyrolysis temperatures in the first cycle and the last but third cycle on the microstructure and mechanical properties of 2D-Cf/Si-O-C composites were investigated. The results showed that, when the pyrolysis temperature of the first cycle was 1200°C, 2D-Cf/Si-O-C composites exhibited good mechanical properties, which can be attributed to the better fiber/matrix interfacial bonding. When the pyrolysis temperature of the last but third cycle was 1400°C, the mechanical properties of 2D Cf/Si-O-C composites were further enhanced. The flexural strength and fracture toughness of the composites reached 263.9MPa and 12.8 MPa·m1/2, respectively.

Abstract: C/SiC, C/Si-O-C and C/C composites reinforced with T300 carbon fiber were fabricated via polycarbosilane (PCS), polysiloxane (PSO), and phenolic resin precursor polymers infiltration/pyrolysis, respectively. Flexural strength and fracture toughness of the composites were evaluated. The results showed that all the composites had poor mechanical properties, less than 160 MPa in flexural strength and 5 MPa•m1/2 in fracture toughness. Deep investigation illuminated that the fiber was damaged severely during the preparation of the composites, especially in the first cycle of precursor pyrolysis. Great degradation of the fiber has relationship with coarsening of the microstructure. Bad in-situ strength of the fiber resulted in poor performance of the composites.