Materials Science Forum Vols. 704-705

Abstract: Activated carbons (ACs) were prepared from lignite by microwave heating with KOH as activation agent, the effects of the weight ratio of KOH to coal and microwave heating time on the pore structure of ACs were investigated by N₂ adsorption. The electrochemical characteristics of electrochemical capacitors (ECs) with ACs as electrodes in 3mol/L KOH electrolyte were evaluated by galvanostatic charge/discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that the BET specific surface area and total pore volume of ACs (denoted as AC-R3) can reach 2097m²/g and 1.19cm³/g respectively when the weight ratio of KOH to coal is 3:1 and the microwave heating time is 10 min. The ECs with AC-R3 as electrodes presents a high specific capacitance of 335F/g at a low current density of 50mA/g and still remains 288F/g even at a high current density of 5A/g, it has excellent cycling stability and low leakage current, and the residual specific capacitance is as high as 93.6% after 1000 cycles under the current density of 2.5A/g. The results have demonstrated that the microwave heating with KOH activation is an efficient approach to prepare ACs with high performance for ECs. Keywords: Activated Carbons; Microwave Heating; Electrochemical Capacitors; Electrochemical Characteristics

Abstract: A noval wear resistant Mo_ss-toughened Mo₂Ni₃Si metal silicide alloys was designed and manufactured with the commercial Mo, Ni and Si powders. Wear resistance of the alloys was evaluated under dry-sliding wear test condition at room temperature. Results show that the alloys have excellent wear resistance and tribological compatibility coupling with conventional metallic materials due to the high hardness and strong atomic bonds of the ternary metal silicide Mo₂Ni₃Si with MgZn₂ type Laves crystal structure.

Abstract: Selecting a single piece of typical rectangular open planar magnet，with its axial magnetization, to build a finite element model. Based on ANSYS software, the article used NdFeB45 material properties, giving 100×100×10mm to fit the relationship of three-dimensional size. In the air zone as 10 times as model size, it adopted a static simulation analysis of the effect on relationship between axial magnetic distance and magnetic field strength. The magnetic field contours as simulation results, after the Origin software fitting process, obtained an equation is: ; Comparing with the formula: , which reflected the basic characteristics of permanent magnetic field, and with the numerical results by Jing-tian LI using equivalent magnetic charge method, they all appeared: the magnetic field strength exponentially decrease along with the magnetic distance increases, the magnetic field non-uniformity coefficient is of 4.628% deviation, the fitting correlation coefficient R is 0.99924; As a result of the numerical verification results, it also visually response to the magnetic field parameters of open permanent magnet.

Abstract: In this paper , by SEM、EDS、XRD and Shimadzu AG-I250KN precision universal testing machine , the metallurgical structure, fracture appearance, the mechanical properties of the ZA303 under high temperature were systematically studied .The results shows that :The microstructure of ZA303 at room temperature are : α phase + (α＋η) _eutectoid + ε phase + η phase. After adding modifying elements B、Ti in ZA303：the microstructure of the alloy is from gross dendrites to uniform equiaxed grains , the quantity, morphology and distribution of the (α + η) have greatly change: the quantity of (α + η) is less, from a continuous network to intermittent block, and its end become blunt, or even cylindrical horn and dispersed distribution; on the grain boundary, the size of ε phase become smaller and dispersed distribution, the number of mesh ε phase reduced but intermittent strips increased; adding B、Ti have a good effect of restraining Al element segregation，so the foundry defects decreased obviously. In the range of experimental temperature, the increase of ductility is large while the tensile strength is small: at the same time, the mechanical performances stability is better than that without modification.

Abstract: Immune algorithm is a computational intelligent method which imitates the information processing properties of the natural immune system. It is one of the effective global optimization algorithms with higher global convergence. In this paper, mathematic model between the mechanical properties and the constituent of Al2O3 based ceramic tool and die material is established with the method of regression analysis. The obtained relationship function works as the optimum objective function. The immune algorithm is then used to optimize the mechanical properties of material. The best value of fracture toughness, hardness and flexural strength is 5.356 MPa·m1/2, 20.702 GPa and 731.96 MPa, respectively. The volume fractions of SiC and Ti (C,N) can be obtained when the mechanical properties of material reach the optimum. The result shows that using immunity algorithm can find the global optimal solution rapidly, and avoid the premature convergence phenomena existed in the genetic algorithm. Comparing the optimal results with experimental results, the relative error is small. It suggested that the immune algorithm can well be used for the optimum design of ceramic tool and die materials.

Abstract: The joint of rock mass influences and controls the rock mass intensity, deformation characteristics and instability failure in the rock engineering to a great extent. Using the similar material simulation is of different inclination angle of non-penetration jointing and non-jointing rock mass, through using rigid servo compression machine to carry uniaxial compression test, we get a nearly same trend of joint rock mass stress-strain curve of different angle, the curve of inclination angle of 45 is analyzed, the test result shows that the compressive strength first decreases and then increases gradually with the increase of rock inclination angle. The compression intensity is its minimum when of the inclination angle of 45°, and the deformation modulus first decreases and then increases, but deformation modulus of 30° is its minimum. In addition, through the use of developed RFPA2D system to simulate on trial uniaxial compression value based on microscopic damage mechanics, we get the conclusion that the numerical analysis and test result is fitting approximately, it is validated that the numerical model can simulate joint rock well. Keywords: joint rock mass, inclination angle, uniaxial compression, compressive intensity, deformation modulus

Abstract: Effects of AlN addition on the microstructure and mechanical properties of as-cast Mg-Al-Zn magnesium alloy were investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and tensile testing. Five different samples were made with different amounts of AlN(0wt%, 0.12wt%, 0.30wt%, 0.48wt%, 0. 60wt%). The results show that the phases of as-cast alloy are composed of α-Mg,β-Mg₁₇Al₁₂. The addition of AlN suppressed the precipitation of the β-phase. And, with the increase of AlN content, the microstructure of β-phase was changed from the reticulum to fine grains. When AlN content was up to 0.48wt% in the alloy, the β-phase became most uniform distribution. After adding 0.3wt% AlN to Al-Mg-Zn alloy, the average alloy grain size reduced from 102μm to 35μm ,the tensile strength of alloy was the highest. The average tensile strength increased from 139MPa to 169.91MPa, the hardness increased from 77.7HB to 98.4HB, but the elongation changes indistinctively. However, when more amount of AlN was added, the average alloy grain size did not reduce sequentially and increased to 50μm by adding 0.6wt% AlN and the β-phase became a little more. Keywords: Al-Mg-Zn alloy; AlN; β-Mg17Al12; Tensile strength

Abstract: In this paper, the viscosity of molten Zr₅₀Cu₅₀ alloy was measured by using NaF-CaF₂ covering slag protection combining rotating cylinder method firstly under non-vacuum melting condition. The curve of viscosity and temperature was acquired stably in the temperature range from 1370K to the liquidus temperature (1208K). According the Arrhenius equation form, the viscosity-temperature relation of molten Zr₅₀Cu₅₀ alloy can be fit as the following equation: （1208K50 alloy can be calculated by the above equation in the range of 1370 to 1208K. The viscosity values of molten Zr₅₀Cu₅₀ alloy calculated by Hirai model are relatively small, so the corrected Hirai model was obtained by the measured viscosity data. The viscosities of molten Zr-Cu alloys can be expressed by the following corrected Hirai model: The viscosities of typical molten Zr-Cu alloys were calculated by the above corrected model. The results showed that the viscosities of Zr-Cu alloys are larger at the respective liquidus temperature. The fundamental data were provided for researching the relationship between viscosities of molten Zr-Cu alloys and amorphous form ability.

Abstract: The geometric parameters of the welding joint had an important effect on fatigue strength, so the stress concentration of the typical double sided asymmetric V-notch joint on high speed train was calculated, the relationship between geometric parameters and the stress distribution of the welding joint was analyzed by FEM, also the geometric parameters optimization design of welding joint was proposed. According to theoretical optimization design scheme, the geometric parameters optimization adopted shaping the weld joint by manual TIG welding and processing circle arc on weld toes by milling respectively,. and the fatigue property of the welding joint optimized by different methods was tested. By comparing the experimental results, it was found that manual TIG welding was difficult to obtain the favorable weld toe angle to decrease the stress concentration, and the welding joint was softened obviously. Accordingly, it revealed that the fatigue property was lower than that of initial joint in fatigue testing. On the contrary, the radius of the weld toes circle arc can be controlled accurately by mechanical processing. The stress concentration was reduced obviously by rounding off the weld toe, as a result the fatigue strength of the welding joint could be increased remarkably. Keywords: A7N01, optimization design, geometric parameters of welding joint, FEM

Abstract: Cold Gas Dynamic Spraying (CGDS) has been developed to fabricate surface coating as a new technique in recent years. In this paper, aluminum bronze particles were sprayed on 45 steel and 316L stainless steel by CGDS, and the coating was sucessfully fabricated on the surface of the steels. The microstructure of the coating and the interface between the coating and the substrate were investigated by scanning electron microscope (SEM), energy dispersive (EDX) and XRD. It was found that the coating was dense and its porosity was low, while the microhardness of the coating was lower than that of the bulk one; Mechanical bonding was the main formation mechanism of the coating, and there was metallurgical bonding too; Diffusion occured at the interface between the coating and substrate; α phase in aluminum bronze particles transformed to β phase after the spray and the transformation was induced by the plastic strain during spraying.