Papers by Author: Ji Cheng He

Abstract: The bubble disintegration is of great scientific importance in metal refining, In order for further improvement, Research on bubble disintegration and dispersion becomes necessary, The intensification of bubble disintegration experiment that we have done in cold water model by study absorption rate ,The purpose is to research bubble disintegration under difference experimental condition . In this paper, we use mass transfer coefficients stand for absorption rate, we also study utilization rate, we want to research the best experimental condition which can enhance mass transfer coefficients and utilization rate. On the basis of experimental result, Provided a scientific and experimental basis to high-temperature experiment of bubble dispersion and disintegration .Experimental results show:the rate of absorption of CO2 injected in aqueous NaOH solution can be increased greatly by mechanical stirring when the positive-reverse rotation mode is adopted. Dispersion of small bubbles in the liquid is very effective for increasing the absorption rate.

Abstract: The effect of a high magnetic field (up to 12T) on the lamellar eutectic spacing changes was investigated in the diffusion liquid Al/solid Cu. It was found that the lamellar eutectic alloy is formed in the diffusion process and its spacing has the non-monotonic relationship with the magnetic field intensity. With the increase of magnetic field intensity, the lamellar eutectic spacing decreases rapidly. When the magnetic field intensity B exceeds 4T, the lamellar eutectic spacing begins to increase until 8T, and then, decrease again. This phenomenon could be attributed to the effects of high magnetic fields suppressing nature convection and inducing thermo-electromagnetic convection in the liquid Al.

Abstract: In the fragmentation theory of T. Campanella et al, the local remelting of dendrite arms is induced by the solute-rich fluid flow. Based on this theory, the effects of linear EMS intensity and solute content on CET of steel are investigated. The conclusions are as follows: The criterion for dendrite fragmentation under linear EMS is derived based on dendrite fragmentation theory by T. Campanella et al. And the criterion is verified with steel experiments. It is valid for steel under the Linear EMS. Investigation is carried out on relation between critical volume fraction of solid and solute content at the time of dendrite fragmentation (CET occurrence). It is concluded that critical volume fraction of solid is small with low EMS intensity and it decreases with the increase of solute content (C, Mn). The reason is that it causes that flow in the mushy zone becomes small which leads to CET occurrence difficult.

Abstract: In order to understand the effects of deoxidizer such as titanium, zirconium and magnesium on the impact toughness of heat affected zone (HAZ) of steel, four low carbon steels deoxidized by titanium, zirconium and magnesium were obtained. After smelting, forging, rolling and welding simulation, the effects of Ti, Zr and Mg additives on the impact toughness of HAZ in low carbon steel were studied. The inclusion characteristics (size, morphology and chemistry) analysis, Charpy-type test and the fracture observation of the specimens after the Charpy-type test were carried out respectively. The following results were found. The density of inclusion in Ti-Zr-Mg deoxidized steel is maximal. With the increasing of Ti content in steel, the proportion of inclusions in diameter less than 0.5 μm decreases. The proportion reaches maximum 64.0% in Ti-Zr-Mg deoxidized steel. The addition of Ti-Zr-Mg can enhance the impact toughness of HAZ after welding simulation. The maximal impacting energy is 249J at 253K. The complex particles of MgO-ZrO2-TiOx-MnS are most benefit to enhance impact toughness. The improvement of HAZ is attributable to the role of particle pinning and the formation of intergranular ferrite.

Abstract: In order to investigate the effects of Ti, Zr deoxidants on inclusions and microstructure of low carbon steel, the experiments by Ti and Zr addition were carried out. After smelting, forging, and rolling of the steel, the effects of Ti and Zr deoxidation on inclusions and steel microstructure were studied. The inclusion characteristics (size, quantity, morphology and composition) of samples were analyzed using optical microscope and scanning electron microscopy (SEM), and the grain size and density were measured. The following results were found. The diameter of most inclusions is less than 3 μm. A linear relationship exists between inclusions density and Ti content when Ti content ranges from 0.004% to 0.032%. With the increasing of the Ti content in steel, the proportion of inclusions diameter less than 0.5 μm decreases. The inclusions distribution changes a little when Ti content ranges from 0.01% to 0.03%. The typical inclusions are TiN and TiN-MxOy, with oxide core and MnS wrapper layer, and the components change with Ti content. The average grain equivalent diameter ranges from 11.8 to 15.9 μm in the experiments. The consistent linear relationship exists between grain density and the total density of the inclusions with the diameter range from 0.5 to 3 μm.

Abstract: A coupled numerical simulation of magnetic field and flow field was conducted basing on Φ250mm bloom during continuous casting with electromagnetic stirring.The distribution of the flow field was analyzed in different current and frequency.At the same current,the velocity first decrease and then increase as the frequency increase along the casting direction.At the same frequency, tangential velocity is dominant in the radial of EMS center,velocity increase with the current. Considered the results of numerical simulation,the optimized EMS parameters of Φ250mm bloom are the stirring current of 480A and the stirring frequency of 3Hz.

Abstract: The effect of electromagnetic stirring on the inner quality and solidification microstructure of the GH 3030 superalloy ingots was investigated by casting experiments. As we know from the experiments, the solidification microstructure of GH3030 is the single-phase of austenite. With the electromagnetic stirring (EMS) the grains of the GH3030 ingots become finer significantly and the average grain size decrease as the currents of EMS increase. The results also show that the macrostructure of the ingots was improved significantly. The length of the shrinkage cavity with EMS become smaller and the porosity disappeared while the ingots without EMS have much porosity. And yet the macrosegregation always exists whether with EMS or not, but the chromium in the ingots with EMS is better distributed, and consequently the macrosegregation of chromium is inhibited.

Abstract: The Cu-12.8wt%Fe alloys are prepared in a vacuum induction furnace and then drawn to Cu-Fe composite wires with the drawing ratio of 8.2. The thermal stability of Fe filaments in the deformed Cu-12.8wt% Fe composite wires under different annealed temperature is investigated. The results show that the instability of the Fe filaments in the Cu-Fe composites is controlled by the longitudinal boundary splitting, then the splitting Fe filaments subsequently evolve into the cylinders. The thermal instability of the cylindrical Fe filaments is controlled by the two instability modes of Rayleigh perturbation and two dimensional Ostwald coarsening. The model calculations of two modes indicate that the perturbation breakup of cylindrical Fe filaments firstly occurs at the ones with smaller diameter. The breakup time of cylindrical Fe filaments decreases with the increasing of the annealing temperature. The coarsening diameters of cylindrical Fe filaments increase in linear proportion with the holding time. The smaller is the diameter of cylindrical Fe filaments, the larger is the coarsening rate.

Abstract: In this paper, the Cu-Fe alloys are fabricated by solidifying with and without a 1.0 Tesla horizontal magnetic field and they are drawn to composite wires under different drawing ratios, then their further strength and conductivity are investigated. The results show that, when the drawing ratio is lower, the strength of the Cu-Fe composites pre-solidified with a horizontal magnetic field is lower, which is caused by the coarser solidification microstructures induced by the injected magnetic field. However, the increase ratio in the strength of the Cu-Fe composites, which is plotted as a function of the Fe content and the drawing ratio, is higher in the case of the imposed magnetic field. It indicates that it is more efficient applying the magnetic field to fabricate Cu-Fe composites with high Fe contents and larger drawing ratio. A quantitative relationship is fitted to predict the influence of the Fe content on the strength of the Cu-Fe composites wires. On the other hand, the conductivity of the Cu-Fe composite wires is decreased with increasing Fe content. The injected magnetic field has no effect on the conductivity.

Abstract: The microstructural changes of the primary Al3Ni phases in hypereutectic Al-Ni alloys solidified under various high magnetic field gradients were investigated. It was found that the application of a magnetic field gradient induced an aligned structure of the primary Al3Ni phases similar to those in a high uniform magnetic field. However, the high magnetic field gradient showed more obvious effect on the alignment of the primary Al3Ni phases than the uniform magnetic field, although this effect strongly depended on the alloy composition.