Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material最新文献

The mechanical properties of transformation induced plasticity (TRIP) steel are strongly affected by the conditions of isothermal bainitic processing. The multiphase microstructure of TRIP steel under different conditions of isothermal bainitic processing was investigated using OM, SEM, XRD and TEM. The volume fraction of retained austenite and the carbon content in austenite were determined quantitatively using X-ray diffraction patterns. The relationship between mechanical properties and isothermal bainitic processing parameters was investigated. The stability of retained austenite was analyzed by the volume fraction of retained austenite and the carbon content in retained austenite. The experimental results show that the multiphase microstructure consists of ferrite, bainite and metastable retained austenite. To obtain good mechanical properties, the optimal conditions of isothermal bainitic temperature and holding time are 410-430°C and 180-240 s, respectively. After isothermal bainitic processing under the optimal conditions, the corresponding volume fraction of retained austenite is 5vol%-15vol%, which can provide enough retained austenite and plastic stability for austenite with high carbon content.

Plasma surface alloying of element Nb in TiAl-based alloys and the oxidation behavior were studied. The composition and microstructure of the surface alloyed layers were investigated by means of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD). The experimental results indicate that the diffusion layers are formed on the TiAl substrate during the plasma niobizing process. The result from oxidation resistance investigation shows that plasma niobizing greatly improves the oxidation resistance of TiAl compared with the untreated TiAl. The role of element Nb for improving the oxidation resistance is considered to be achieved by strengthening the activity of Al, which is induced by the plasma niobizing process.

The microstructure and composition of the residual liquid at different temperatures were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDX) associated with the Thermo-calc software calculation of the equilibrium phase diagrams of Inconel 718 and segregated liquid. The liquid density difference and Rayleigh number variation during solidification were estimated as well. It is found that the heavy segregation of Nb in liquid prompts the precipitation of δ and Laves phase directly from liquid and the resultant quenched liquid microstructure consists of pro-eutectic γ+eutectic, or complete eutectic according to the content of Nb from low to high. The liquid density increases with decreasing temperature during the solidification of Inconel 718 and the liquid density difference is positive. The largest relative Rayleigh number occurs at 1320°C when the liquid fraction is about 40vol%.

A new method was reported for surface modification of an up-conversion luminescence material with hydrosulfide group. The factors that may influence the surface modification, such as reaction time, amount of catalyzer and modifier, and reaction solvent, were investigated. The optimal conditions were that the reaction time, the quantity of the basic catalyzer, the quantity of modifier and the volume of reaction solvent were 40 min, 1.0, 1.0, and 40 mL, respectively. The results indicated that hydrosulfide group content modified on the surface of up-conversion luminescence material reached to 0.1430 mmol/g, and this modified up-conversion luminescence material could be widely used in the study of structure of protein and the property of microenvironment.

The fast cooling rate of thin ductile iron castings requires special consideration to produce carbide-free castings. Extraordinary care was taken to select the charge to produce castings of 100-mm long round bars with 16-mm diameter. The castings show the presence of carbides in the bars. Seven melts were made with different temperatures and with different compositions to get rid of carbides. After chemical analyses, it was found that the extra purity of the charge with less than 0.008wt% sulfur in the castings was the cause of carbides. To remove the carbides from the castings, sulfur should be added to the charge.

It is essential for alumina production by alkaline process to know the behavior of minerals containing Al and Si in basic solution, and the behavior of SiO₂ in the process of clinker leaching is an important portion. To study the behavior of SiO₂ in the process of high concentration clinker leaching, experiments were carried out in home-made reactors. The results indicate that factors, such as temperature, time, Al₂O₃ concentration, as well as SiO₂ concentration, have profound impact on the SiO₂ and Al₂O₃ concentration of pregnant liquor during the high concentration leaching. However, sodium carbonate and free caustic soda concentrations have no remarkable effect on it, thus they are the secondary factors compared with Al₂O₃ concentration. The concentration of SiO₂ in the pregnant liquor could be reduced to a lower level when the major effect parameters of this process are controlled properly.

Magnetic Co-P thin films were prepared by electroless deposition. The experiment results show that the film thickness has a significant influence on the coercivity. While the film thickness varied from 300 nm to 5 μm, the coercivity dropped sharply from 45.36 to 22.28 kA/m. As the film thickness increased further, the coercivity varied slowly. When the thickness of the film was 300 nm, the deposited film could realize the coercivity as high as 45.36 kA/m, and the remanent magnetization as high as 800 kA/m. The Co-P films were deposited on the surface of magnetic drums of encoders, whose diameter was 40 mm, and then 512 magnetic poles were recorded, meaning that the magnetizing pitch was 0.245 mm. The testing results indicate that the output signals are perfect, the output waveforms are steady and the pulses account is integral. Compared with the γ-Fe₂O₃ coating, the Co-P thin film is suitable to be the magnetic recording media for the high resolution magnetic rotary encoder.

Direct current metal filtered cathodic vacuum arc (FCVA) and acetylene gas (C₂H₂) were wielded to synthesize Ti-containing amorphous carbon films on Si (100). The influence of substrate bias voltage and acetylene gas on the microstructure and mechanical properties of the films were investigated. The results show that the phase of TiC in the (111) preferential crystallographic orientation exists in the film, and the main existing pattern of carbon is sp². With increasing the acetylene flow rate, the contents of Ti and TiC phase of the film gradually reduce; however, the thickness of the film increases. When the substrate bias voltage reaches −600 V, the internal stress of the film reaches 1.6 GPa. The micro-hardness and elastic modulus of the film can reach 33.9 and 237.6 GPa, respectively, and the friction coefficient of the film is 0.25.

A universal thermodynamic model of calculating the mass action concentrations of components in a ternary strong electrolyte aqueous solution has been developed based on the ion and molecule coexistence theory, and verified in the NaCl-KCl-H₂O ternary system at 298.15 K. To compare the difference of the thermodynamic model in binary and ternary strong electrolyte aqueous solutions, the mass action concentrations of components in the NaCl-H₂O binary strong electrolyte aqueous solution were also computed at 298.15K. A transformation coefficient was required to compare the calculated mass action concentration and reported activity because they were obtained at different standard states and concentration units. The results show that the transformation coefficients between calculated mass action concentrations and reported activities of the same components change in a very narrow range. The calculated mass action concentrations of components in the NaCl-H₂O and NaCl-KCl-H₂O systems are in good agreement with the reported activities. This indicates that the developed thermodynamic model can reflect the structural characteristics of solutions, and the mass action concentration also strictly follows the mass action law.

Because there are a lot of influences of alumina inclusions on the performance of rail steel, it is reasonable to adopt the deoxidization method with Al-free deoxidizer. According to the characteristics of Al-free deoxidization process, the control of aluminum content, the deoxidization with ladle furnace(LF) slag, the deoxidization process under vacuum by carbon, and the inclusions modification technology by calcium treatment were studied. All of them were applied to practical production. The results indicate that the adoption of Al-free deoxidization process leads to the total oxygen content in the steel below 20 ppm, which meets the requirement of clean rail steel.