Guo Zhang Tang

Effect of Current Density on Composition and Microstructure of Si Diffusion Layer by Electrodeposition

A Si diffusion layer on grain-oriented low-silicon steel substrates was produced by pulse electrodeposition in KCl-NaCl-NaF-SiO2 molten salt and the effect of current density upon the composition and microstructure of the siliconized layer was investigated. The results showed that by glow discharge spectrometry (GDS), the change of Si content of siliconized layers was similar in the range of 20-60 mA/cm2. Si content in the surface was maximum, and then dropped sharply within the surface layer (< 7 m). The Si content remained nearly constant in the middle part of the siliconized layer. The content of Si near to the substrate decreased relatively slowly. The Si content in the surface and the layer thickness increased with increasing current density. Cross-sectional observations revealed that the Si diffusion layers had a two-layer structure: the top layer composed of columnar grains grown perpendicularly to the substrate surface and a transition layer with equiaxed grains was close to the substrate. In addition, the thickness of the layer was too small when the current density was 20 mA/cm2, while the layer became more porous as the current increased from 40 to 60 mA/cm2 according to SEM observations. The optimum current density for deposition was 30 mA/cm2.

Growth Kinetics and Microstructure of Siliconized Layer by Molten Salt Electrodeposition

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.

Effect of Frequency on Composition and Microstructure of Siliconized Layer Using Pulse Electrodeposition

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.

Influence of Duty Cycle on Composition and Microstructure of Siliconized Layer Using Pulse Electrodeposition

The siliconized layer was pulse electrodeposited on grain oriented low-silicon steel sheet substrate in KCl-NaCl-NaF-SiO2 molten salts and the influence of duty cycle on the composition and microstructure of the siliconized layer was investigated. The results showed that when the duty cycle was in the range of 10% to 50% at average current density 30mA/cm2, Si content of siliconized layers was similar and the thickness of the layer was did not change much with different duty cycle. Cross sectional observation revealed that the siliconized layers had a two-layer structure. The top layer composed of columnar grains and a transition layer with equiaxed grains was close to the substrate. The layer was unsmooth when the duty cycle was 10%. While the surface appeared smooth and dense and the grains were fine when the duty cycle were 20% and 30%. The layer became more porous as the duty cycle increased to 40% and 50%.

Growth Characteristics of Pulse Electrodeposition Fe-Si Layer

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

Process Optimization and Structural Characterization of Fe3Si Layer by Pulse Electrodeposition

Fe3Si layer was prepared by pulse eletrodeposition of Si on the surface of non-oriented steel in molten salts. With an orthogonal test the optimal process parameters were determined: the formulation of salts was NaCl:KCl:NaF:SiO2=1:1:3:0.3(mole ratio), current density of 60 mA/ cm2, duty cycle of 30%, pulse period of 1000 s and a deposition time of 50 min, respectively. The compositional depth profile, the structure, the surface morphology and cross sectional micrograph of the layer were studied by glow discharge spectrometry (GDS), X ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscope (OM). The results showed that Si in the layer existed in the form of the gradient distribution. The phase structure of the layer was composed of the single-phase Fe3Si. The layer composed of equiaxed grains. The surface appeared smooth and dense, and with uniform thickness.

Methods of Porous Biomedical Material Fabrication

The development history of biomedical titanium alloy was reviewed in this paper. Because of high recovery strain, low stiffness facilitating integration with bone structures and good market potential of porous biomedical material, the most common methods for fabricating porous biomedical material were introduced. The advantages and disadvantages of the methods were summarized from the aspects of process route, reaction mechanism and porosity. The main direction for further studies in this field was also suggested.

Effect of the Duty Cycle on Boronized Layer Formed by Pulse Electrodeposition

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%.

Optimization on Heat Treatment Process of 45CrMnSi Steel by Orthogonal Test

The effect of quenching temperature, tempering temperature and tempering time on hardness of 45CrMnSi steel was studied by orthogonal test. It was found that the order of significant factors for the hardness was quenching temperature > tempering temperature > tempering time. Based on the results of the range analysis, the optimum process parameters for the maximum hardness were that the quenching temperature was 900°C, the tempering temperature was 150°C, and the tempering time was 180 min. Under the optimum process conditions, the hardness reached to HRC52 with impact toughness of 15 J/cm2. The hardness and toughness met the need of the comprehensive mechanical property and proper toughness of 45CrMnSi.

Preparation of High Silicon Steel by Pulse Electrodeposition in Molten Salt

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.