Applied Mechanics and Materials Vols. 423-426

Abstract: The inelastic response constitutive description of metal material under different stress and wide temperature range is very important in many practical engineering. It can accurately reflect the level of material rate sensitivity and set up a simple and practical strengthening evolution rate. Take No.35 steel as an example; because of the action of load, temperature, time and other factors in its forming process, the creep relation is very important and complex. In view of this situation, the BC-BPNN (Based on Back propagation Neural Network), owing high precision nonlinear fitting ability has and good generalization ability, is applied to the research on creep constitutive relationship of 35 steel. At first, the creep relationship is numerically fitted using testing data of 35 steel; then, the fitting results is compared with the creep testing data. The results show that the applying of BC-BPNN to research on metal creep relationship has a strong practical value.

Abstract: In this work, the mechanical properties, such as Vickers microhardness H_v, fracture toughness K_c, yield strength σ_v and brittleness index B_i, of <0001> oriented 6H-SiC crystal are systematically evaluated using a microindentation technique under 0.1-2 kg applied load. It is found the H_v is decreased as the applied load is increased which is mainly attributed to the effect of indenter penetration. The H_v value can be effectively presumed by Kicks law and the Meyers index n is determined to be 1.73. However, the K_c value is measured nearly a constant (~0.148 MPa.m^1/2) which reveals the toughness of 6H-SiC₍₀₀₀₁₎ crystal is much weaker than those of Si₍₁₀₀₎ and GaAs₍₁₀₀₎ crystals. The variation of σ_v to the load is similar to that of H_v. The brittleness index B_i also exhibits deceasing tendency as the applied load is added.

Abstract: As advanced semiconductor materials, Ga_1-xAl_xN alloys are widely used. In order to research the optical properties of Ga_1-xAl_xN with different Al component, we built models of GaN, Ga_0.875Al_0.125N, Ga_0.750Al_0.250N, Ga_0.625Al_0.375N, and AlN, and calculated the optical properties of the five crystals based on first principle calculations. Results show that the static dielectric constant decreases when the Al component increases, and the absorption peak shifts to higher energy. The threshold wavelength of Ga_1-xAl_xN is lower and lower when the Al component increases, and the Ga_1-xAl_xN material owns “solar blind” property when the Al component is higher than 0.25.

Abstract: To investigate the fatigue property of A356 cast aluminum alloy, the pore size distribution in two kinds of A356 alloy were statistically tested, and the S-N curves were plotted by conducting four-point bend fatigue test, then the fractography of the fatigue specimens were examined under scan electron microscope (SEM). It was indicated that the fatigue strength of the A356.2 alloy contenting more large pores and rougher crystalline grain was lower than that of A356.1 alloy, though the yield strength of A356.2 alloy was higher. Most of the fatigue cracks initiated from the pores that located on or close to the surface of the specimens, and the fracture of the specimens were induced from the growth of multi-sites initiated fatigue crack.

Abstract: To enhancing strength and toughness of metals, severe plastic deformation (SPD) grain refinement was a typical method. As one of the SPD method, equal channel angular pressing is an effective method in fabricating ultra-fine grain metallic materials. In this paper, the rigid-plastic finite element method was used to analyze the aluminum alloy ECAP processing, to reveal the material flow character and its effect on microstructure evolution. The simulation results were agreed with plastic mechanics and experiment well, and it was shown that distribution of maximum principal stress was not uniform, material located at the front-end of sample flow easily and material located at the top of die channel corner flow difficultly.

Abstract: We have measured magnetic Compton scattering (MCS) for an Fe/MgO multilayer film at several magnetic field applying perpendicular to film plane. A spin specific magnetic hysteresis (SSMH) loop is obtained by the MCS for the Fe/MgO multilayer film. A knickpoint is observed in the SSMH loop around the magnetic field of 0.5 T. Orbital magnetization is enhanced within the magnetic field from-0.5 T to 0.5 T. A decomposition analysis for magnetic Compton profiles shows the suppressed |m|=0 states and enhanced |m|=1 and 2 states within the magnetic field from-0.5 T to 0.5 T. Here m denotes magnetic quantum number. The knickpoint corresponds to a perpendicular magnetic anisotropy, which comes from the enhanced |m|=1 and 2 state and orbital magnetization in the Fe/MgO multilayer.

Abstract: High current pulsed electron beam (HCPEB) treatment was conducted on 40CrNiMo7 steel. The surface microstructure was characterized by metalloscopy and X-ray diffraction methods. The microhardness and wear resistance of modified surface were measured. After the HCPEB treatment, the surface crater structure was observed due to the inhomogeneity of initial material. A modified layer of depth ~ 7 μm was formed with a hybrid microstructure composed mainly of martensite and a small quantity of austenite. The surface microhardness of HCPEB modified sample was increased drastically to more than 1000 HK. The wear resistance increased by about 36% as compared to the initial state.

Abstract: The microstructure evolution laws of ultrafine grained metastable automobile steels was studied in this paper by laser confocal scanning microscope, EBSD, XRD and TEM. Results showed that, the matrix organizations of hot-rolled steel were lath martensite and deformation ferrite, and there were a little of retained austenite film and lath between the lath martensite. After heat treatment, the matrix organizations of steel were ultrafine ferrite and retained austenite. The retained austenite transformed into martensite and ε-martensitic in the deformation process, and the strength and plasticity of steel were improved. A lot of retained austenite were obtained in the annealing process. The TRIP effects by the large fraction of metastable austenite and the ultrafine grain size add to the test steel with high strength and high plasticity.

Abstract: Different alloy composition has a significant effect on the magnetic properties of non-oriented electrical steel . Alloy composition effected recrystallization of product through the effect of hot rolling plate grain size, then effected magnetic properties. Supposing everything other component and process remain equal, the iron loss significantly decreased and magnetic induction deterioration was not obvious with the increase of Manganese element and the grain size increases.

Abstract: Many factors affect the phase, chemical composition, heating rate, cooling rate, microstructure, deformation will affect the phase transformation. Laboratory testing of finished the test used with different chemical composition, but the heating rate, cooling rate, microstructure and deformation degree are the same. Through differential thermal analyzer (DTA) measurement of phase transformation temperature of the samples, explain the effect of different alloy composition of non-oriented electrical steel phase transformation.