Papers by Author: Yun Gang Li

Abstract: Fe-Si layer was prepared on silicon steel substrate from KCl-NaCl-NaF-SiO2 molten salts by pulse current at different time. The quantitative Si concentration depth profile, surface morphology and phase structure of the layer were studied by glow discharge optical emission spectroscopy, atomic force microscopy and X-ray diffraction. The layer growing process was analyzed from nucleation process, growth pattern and microstructure. It was observed that the Fe-Si alloy nucleated in the way of three dimensional conical shape and initially grew in the orientation of matrix, then gradually adjusted to the lowest energy state. With deposition time going on, the phase structure of the layer changed in the order of -Fe (Si) →α-Fe (Si) ＋Fe₃Si →Fe₃Si

Abstract: Boronized layer on silicon steel substrate was fabricated using pulse electrodeposition technique with different duty cycle in KCl-NaCl-NaF-Na₂B₄O₇ molten salts. The effect of the duty cycle on composition and microstructure of obtained layer was investigated. The boronized layer was analyzed by X-ray diffraction analysis (XRD), optical microscopy (OM), glow discharge spectrometry (GDS), and atomic force microscopy (AFM). The results showed that in the range of 10-50%, duty cycle almost had no effect on composition and thickness of the layer. The boronized layers in this range exhibited FeB phase on the surface of silicon steel. However, duty cycle had great effect on the microstructure of the boronized layer. A fine grain size boronized layer can be obtained at a duty cycle of 20%.

Abstract: By summarizing the research and development status of electro-thermal materials, this thesis puts its focus on the types, preparation methods and applications of non-metallic high-temperature electrothermal materials, and the comparative analysis of the advantages and disadvantages of such electric heating elements as SiC, ZrO₂, LaCrO₃ and MoSi₂. At last, the gap and the main problems existing between researches made on high temperature electrothermic materials at home and abroad are pointed out, as well as their prospected development trend.

Abstract: Boronized layer was prepared on carbon steel substrate by pulse electrodeposition in KCl-NaCl-NaF-Na2B4O7 molten salts. The orthogonal experimental design was used to study the influence of pulse electrodeposition parameters on the thickness of boronized layer. The distribution of boron content of the boronized layer was measured using the glow discharge spectrometry (GDS) and the depth from the surface to the inflection point was taken as the layer thickness. It was found that the order of significant factors for the thickness is electrodeposition temperature > electrodeposition time > current density > borax content > duty cycle. Based on the results of the range analysis, the maximum thickness was found at a current density of 120mA/cm2, a electrodeposition temperature of 900°C, a electrodeposition time of 120 min, a duty cycle of 10%, and a borax content of 0.04 mole ratio.

Abstract: Boronized layer was prepared on silicon steel substrate by pulse electrodeposition in KCl-NaCl-NaF-Na2B4O7 molten salts with different current density. The effect of current density on composition and microstructure of boronized layer was studied. The phase, the cross-sectional morphology and the compositional depth profile of the layer were studied by X-ray diffraction analysis (XRD), optical microscopy (OM) and glow discharge spectrometry (GDS). The presence of FeB on the surface of the boronizied steel was confirmed by XRD analysis. Cross sectional observation revealed that the boronized layer consisted of the outer layer FeB and the sublayer Fe2B. In addition, the low current density produced more proportion of Fe2B and bigger saw-tooth grains.

Abstract: By summarizing the research and development status in recent years, this thesis especially introduces the preparation method and enhancement mechanism of the functionally gradient material of Mo-MoSi₂. Results of experiments show that: alloying and compounding can significantly improve the room-temperature brittleness and high temperature strength；and the application of Chemical Vapor Deposition (CVD) method in the preparation of Mo-MoSi₂ multiphase anti-oxidation coating, has obvious advantages in that it reduces cracking and improves the coating quality. Finally, the developing trend of Mo-MoSi₂ and its prospected difficulties and hot issues are also pointed out.

Abstract: High silicon steel containing 6.5 wt% Si was prepared by pulse electrodepositon in KCl-NaCl-NaF-SiO₂ molten salt followed by diffusion annealing. The composition, the phase and the evolution of texture during the different production step were analyzed by glow discharge optical emission spectroscopy (GDOES), X-ray diffraction analysis (XRD) and the orientation distribution function (ODF). The results showed that the silicon content of the high silicon steel was about 6.5wt%. The high silicon steel was composed of a-Fe and Fe₃Si. After diffusion annealing the undesirable g-fibre type texture {111} <110> and {111} <112> weakened, both easy magnetization direction Goss texture ({110} <001>) and cube texture {100} <001> were intensified.

Abstract: The siliconized layers were formed on the surface of hot rolled grain oriented silicon steel using a molten salt pulse electrodeposition method. The process was performed in the temperature range 1023-1123 K and with varying deposition time (60-180 min). The profile distribution of Si in the siliconized layer was measured using the glow discharge spectrometry (GDS) and the depth from the surface to the substrate was taken as the layer thickness. The morphology and structure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that a longer deposition time tended to produce a larger grain and a looser, rougher layer. The phase structure of the layer was composed of Fe3Si with (110) preferred orientation in the experimental range. The longer deposition time resulted in an increase in thickness layer and the thickness of the layers ranged from 17 to 165m. Kinetic studies showed that the siliconized layer grew with a parabolic rate law, indicating the diffusion controlled growth. The activation energy for growth of siliconized layer was about 242 kJ/mol.

Abstract: The siliconized layer on low silicon steel substrate was produced under pulse current conditions from KCl-NaCl-NaF-SiO₂ molten salt and the effects of frequency on the composition and microstructure were investigated. The results showed that at the same average current density and other experimental conditions, Si content in the surface and the layer thickness decreased with increasing frequency. Low pulse frequency (500 Hz) and high frequencies (1500, 2000Hz) produced coarse grain and bigger surface roughness. There was a flat fine grain structure and a relatively thick (30m) layer when the frequency was 1000Hz. However, the effect of pulse frequency on the structure of the layer was not obvious. The phase structure of the layer was composed of Fe₃Si with (110) preferred orientation at all experimental frequencies.

Abstract: Boronizing of silicon steel is performed by electrodeposition in KCl-NaCl-NaF-Na2B4O710H2O molten salts with different amounts of borax. The effect of borax content on composition and microstructure of boride layer is studied. The compositional depth profile of boride layer is measured using the glow discharge spectrometry (GDS) and the depth from the surface to the substrate is taken as the layer thickness. The surface morphology is studied by atomic force microscopy (AFM). It is found that the thickness of the boride layer reached maximum values when the borax content is 0.05mol. The roughness decreases with raising borax content from 0.01 to 0.05mol while the further increase of borax content from 0.05 to 0.1mol results in increase of roughness. The boride layer formed at borax content 0.05 mol shows smallest values of surface roughness.