Papers by Author: Jian Feng Yang

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Authors: Rong Zhen Liu, Bo Wang, Ji Kuan Cheng, Jian Feng Yang, Ji Qiang Gao
Abstract: A novel method for preparing porous silicon carbide ceramics with high porosity had been developed by recrystallization of green bodies composed of α-SiC, β-SiC, remnant silicon and incompletely-reacted carbon. Fine microstructure and uniform pore structure of the resultant porous silicon carbide ceramics was obtained. The green bodies of porous ceramics were prepared by the precursor powder which contained α-SiC, carbon black and silicon powder. The precursor powder was sintered at 1600°C under Vacuum circumstance to obtain the green bodies; the sintering process is same with the reaction sintering silicon carbide. Then the green bodies were sintered to 2300°C for half an hour to recrystallization. The incompletely-reacted carbon was fully reacted with silicon. And the remnant silicon was excluded during the recrystallization process to create porous structures. The influence of composition of the precursor powder and the fabrication process (the moulding pressure) on the microstructure of sintering bodies was analyzed. X-ray diffractometry demonstrated the transformation of β-SiC to α-SiC during the recrystallization process. The density and the porosity of this material was 1.027g/cm3 and 67% respectively.
Authors: Hai Tao Wu, Hai Yan Shang, Li Tong Guo, Jian Feng Yang, Tian Wen Guo
Abstract: In the acidic oral environments containing fluoride ions, hydrofluoric acid (HF) would form and affect the color of Titanium porcelain crown, but there is a lack of information on how color is affected by this oral fluid. The purpose of this study was to investigate the effects of various artificial saliva simulating oral environments in the presence of fluoride ions with different pH value on the color of self-made dental opaque, body porcelain, belonging to the Na2O-K2O–MgO–CaO–Al2O3–SiO2 glass system. Disc-shaped specimens, 5 mm diameter and a 2-mm thickness, were made by firing. Specimens were immersed in artificial saliva in the presence of fluoride ions with different pH value for 7, 14, 21 days, and then the color of the specimens was compared with the color of the initial specimen. The interactions were present in L*a*b* values between pH value and the day of immersion. The changes in L*a*b* color data as the day of immersion and pH value increased were revealed, which can resulted in perceptual color changes in L*a*b* color parameters.
Authors: Jie Liu, Guang Wei Fan, Pei De Han, Jian Sheng Liu, Ji Qiang Gao, Jian Feng Yang
Abstract: Effects of nitrogen content on hot ductility of duplex stainless steels have been investigated. With the increase of nitrogen content in the duplex stainless steels, mechanical strength increased, while hot ductility and elongation decreased. With the same strain rates and deformation degree, the high nitrogen content led to the high optimum hot ductility temperature for the high nitrogen DSS alloy. These results indicated the importance of control over the shape and volume fraction of phases in duplex stainless steels to achieve the optimum hot ductility.
Authors: Jian Guang Bai, Guang Liang Liu, Jian Feng Yang
Abstract: A foam ceramic was prepared using clay, SiC, Fe2O3, feldspar and other raw materials as main starting material in a furnace at 1140~1170oC for 15~25min. Effects of silicon carbide’s content and powder size on the bulk density, moisture absorption rate and compressive strength were studied, and the fracture surface morphology was observed and analyzed using Scanning Electron Microscope (SEM) and X-ray diffraction analysis (XRD). The results show that SiC powder reacted with Fe2O3, Fe3O4, CO2, iron, SiO2 and form foam. The sintering behavior and properties of the foam ceramics are influenced by the content and particle size of SiC, when the content of SiC is as high as 8%, and the mass ratio of grain size is 1:1, the foam ceramics with the rate of moisture absorption is 0.05%, the bulk density is 0.32g/cm3, and compressive strength is than 2.2MPa.
Authors: Jian Guang Bai, Bo Wang, Guang Liang Liu, Ji Qiang Gao, Jian Feng Yang, Jing Zhong Zhao, Zhen Li
Abstract: In this paper, cordierite-mullite multiphase ceramics material was prepared using cordierite powder, mullite particles, fused silica, magnesia and alumina as main starting material. Effects of addition of 2%~10% SiC on the thermal expansion, flexural strength and thermal shock resistance were studied, and the fracture surface morphology was observed with Scanning Electron Microscope (SEM). The results showed that the multiphase ceramics material’s thermal expansion coefficient and flexural strength had little change. The thermal shock resistance of cordierite-mullite multiphase ceramics material varied as increasing-decreasing with the increase of SiC content, when the content of SiC was as high as 4%, the highest conservation rate of the flexural strength after 1100°C~water(3 times) was 72.08%, and the thermal shock resistance of cordierite-mullite multiphase ceramics material was superior.
Authors: Guang Wei Fan, Jie Liu, Pei De Han, Guan Jun Qiao, Jian Feng Yang
Abstract: Effect of the warm processing parameters (the strain rate, forming temperature and deformation degree ) on the γ' metastable phase transformation in 2205 duplex stainless steel has been studied. The γ' metastable phase was located within the ferrite phase. Dynamic recovery took place only within the γ phase, and dynamic recrystallization underwent for the ferrite phase. The γ' metastable phase transformation was affected by the deformation degree and about 15% deformation led to appearance of the γ' metastable phase. γ' metastable phase formation by the precipitation of intragranular γ' was favored by increasing ageing time, and the size and content of γ' metastable phase were related to deformation temperature and strain rates.
Authors: Jian Feng Yang, Ji Qiang Gao, Guo Jun Zhang, Ichiro Hayashi, Tatsuki Ohji
Abstract: Porous Si3N4 ceramics with different pore morphology have been fabricated, utilizing either organic whiskers or starch as the fugitive agents, through slip-casting and die-pressing technique, respectively. The obtained porous ceramics have rod shaped or equiaxial pore morphology, originated from there two kinds of pore forming agents. The mechanical properties were investigated. The strength decreased considerably when small amount of whiskers were added, however, further increase in the whisker content only cause a moderate decrease of the strength. Gas permeability were measured for the samples with high whisker content of 60 vol% (corresponding to porosity of about 45% in the sintered bodies), and was compared with the counterpart contained the same porosity in which pores were equiaxial. The flexural strength of the samples with these two types of fugitive particles was almost the same, but the permeability of samples with rod-shaped pores were much higher than that with equiaxial pores, which can be understood in terms of a short pass model.
Authors: Yuan Lu, Jian Feng Yang, Shao Yun Shan, Ji Qiang Gao, Zhi Hao Jin
Abstract: In this paper, porous Si3N4 ceramics were fabricated by carbothermal reduction between silicon dioxide and carbon. The influences of four types of sintering additives on the microstructure and mechanical properties of the porous Si3N4 ceramics were investigated. XRD analysis proved complete formation of a single-phase β-Si3N4. SEM analysis showed that the resultant porous Si3N4 ceramics occupied fine microstructure and a uniform pore structure. The sintered sample with Lu2O3 as sintering additive showed finer, a higher aspect ratio β-Si3N4 grains. The addition of Eu2O3 accelerated the densification of porous Si3N4 ceramics, decreased the porosity and increased the flexural strength.
Authors: Chao Cai, Qiu Ping Wang, Zhao Zhang, Jian Feng Yang
Abstract: The electroplating behavior of nanocrystalline CoNiFe soft magnetic thin film with high saturation magnetic flux density and low coercivity was investigated using cyclic voltammetry and chronoamperometry methods in conjunction with the scanning electron microscopy (SEM/EDX) and X-ray diffraction (XRD) techniques. The results show that, the co-deposition of CoNiFe alloy behaves anomalously. And the nucleation/growth process of CoNiFe ternary alloy followed 3D instantaneous mechanism at higher potentials, while in the case of lower potentials it followed 3D progressive mechanism.
Authors: Bo Wang, Rui Guo, Ji Qiang Gao, Jian Feng Yang
Abstract: The barium aluminum silicate-silicon nitride (BAS-Si3N4) matrix-ceramic composite was fabricated using pressureless sintering, at temperatures ranging from 1720°C, which is below the melting point of BAS, to 1850°C. The effect of processing conditions on sinterability, crystalline structure, microstructure and mechanical properties was evaluated. It was demonstrated the BAS glass-ceramic served as an effective liquid-phase-sintering aid, to attain high densities and completed the α-Si3N4–β-Si3N4 phase transformation, and remained as a structural matrix that was reinforced by the rod-like β-Si3N4 grains. Si3N4 grains nucleated and grow in random directions in an almost completely crystallized matrix of hexacelsian BAS. High flexural strength (665±40 MPa) and fracture toughness (7.74 MPa•m1/2) could be obtained from 30wt%BAS-70wt%Si3N4 samples that have been sintered at 1800°C for 120 min with a fine-grained microstructure.
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