Abstract: Fracture absorption energies of U-notched and pre-cracked samples of a bainitic-austenitic TRIP steel were studied at different loading rates. The results show that the total absorbed energies increase with increasing the loading rate for the two types of samples. For the U-notched samples, both crack initiation and propagation energies exhibit considerably larger values at higher loading rates. However, for the pre-cracked samples, the crack propagation energy increases noticeably with increasing the loading rate, whereas the crack initiation energy does not show an obvious rise with loading rates. These results are discussed in terms of the amount and role of austenite-to-martensite transformation occurring at various loading rates.
Abstract: Fatigue crack growth (FCG) behavior of three high manganese austenitic twin-induced plasticity (TWIP) steels with different stacking fault energy (SFE) was investigated, aiming at studying the correlation between the FCG resistance and the SFE of the steels. FCG tests were performed using three-point bending specimens at room temperature at stress ratio of 0.1 under the control of stress intensity factor range. Test results showed that the fatigue threshold values of these steels decrease with increasing the SFE. However, in the Paris regime, the crack growth rates of the steels do not appear to correlate directly with SFE. These results are discussed according to the degree of fatigue crack closure and the deformation mode of crack tip zone.
Abstract: Phase field method (PFM) was employed to investigate the crystal growth of Mg-Al alloy, on the basis of binary alloy model, the fluid field equation was coupled into the phase-field models, and the marker and cell (MAC) method was used in the numerical calculation of micro structural pattern. In the cast process, quantitative comparison of different anisotropy values that predicted the dendrite evolution were discussed in detail, and when the fluid flow rate reaches a high value, we can see the remelting of dendrite arms.
Abstract: A quantitative understanding of the twin-roll casting process is required to get high quality as-cast magnesium alloy strips. In this paper, a thermal flow-solidification simulation was carried out to study the behavior of casting zone and its effects on defects generation deeply. Results show that a lower pouring temperature is not suitable for producing defect-free magnesium alloy strips. With increasing of the casting speed, the tendency of cracks formation will getting smaller because of the more uniform temperature distribution. A low pool level leads to a small metal-roll contact area, and a sharp temperature distribution will generates under this situation, which is not good for strips quality.
Abstract: A modified 2-D CA model has been developed to simulate dynamic recrystallization behavior of Magnesium (Mg) alloy during hot deformation processing. Based on the fact that Mg has an HCP crystal structure with six-fold symmetry, the model employs the hexagonal CA lattice. The initial microstructure with prescribed grain size was generated by a normal grain growth algorithm. The DRX model consists of dislocation density evolution model, DRX nucleation model and recrystallization grain growth model. DRX grain morphology and size, flow curve were simulated by the present model. The calculated results were compared with the available experimental findings in AZ31 Mg alloy, the predictions show very good agreement with the experimental results.
Abstract: New Cu–Fe-based ternary systems have been developed to fabricate monolithic porous materials through electrochemical dealloying process in a 1.84 mol/L H2SO4 solution. The microstructures of the porous materials were characterized using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The results show that the compositions of the as-melt Cu-Fe-Co and Cu-Fe-Ni alloys have an important effect on the electrochemical dealloying process and microstructures of the monolithic porous materials.
Abstract: The Al-Ti-C master alloy with excessive carbon content was prepared by the self-propagating high-temperature synthesis (SHS) in melt method. The master alloy mainly contains Al4C3 and TiC phases, which exhibits satisfactory refining effect on AZ31 alloy. With 1.5wt.% addition of the master alloy, the grain size reduced from 280 μm to 109 μm. The tensile properties are also improved with the refinement of grain structure. The ultimate tensile strength increased from 105 MPa to 156 MPa while the elongation increased from 8.4% to 13.6%. The Al4C3 particles and TiC particles play important role in the refining process due to their low disregistry with α-Mg grains.
Abstract: Electrocatalytic oxidation activity of oxalic acid can be observed by using a multielectrolytic modified glassy carbon electrode (MMGCE). The MMGCE was fabricated by using the following electrolytic-oxidation/reduction processes. First, the functional groups containing nitrogen atoms such as amino group are introduced by the electrode oxidation of a bare glassy carbon electrode in an ammonium carbamate aqueous solution, and next, this electrode was electroreduced in sulfuric acid, and it was found that the reduction current gradually increased as the electrolysis time increased. This suggests that functional groups containing nitrogen atoms contributing the catalytic electron transfer of hydrogen ion are introduced. To observe the electrode oxidation wave of oxalic acid, the voltammmetric measurements of oxalic acid was carried out by using MMGCE in an acidic medium. The oxidation wave of oxalic acid at low potential range was appeared in the linear sweep voltammograms. The MMGCE exhibited well-defined peak of oxalic acid oxidation in acidic medium.
Abstract: A novel blue-emitting phosphor NaBaBO3 doped with Tm3+ was prepared using a conventional high temperature solid-state reaction method. Its crystal structure and luminescence properties were studied. Photoluminescence measurements indicate that the phosphor features a satisfactory blue performance due to the 1D2→3F4 transition of Tm3+ with the highest photoluminescence intensity located at 460 nm excited by 359 nm near-ultraviolet (NUV) light. In addition, the concentration of Tm3+ was adjusted in order to obtain the optimum emission intensity. When the Tm3+ concentration in NaBaBO3 is 6.0 mol% the maximum intensity can be obtained. The concentration quenching occurs when Tm3+ concentration is beyond 6.0 mol% and the concentration quenching mechanism can be explained by the dipole–dipole interaction. The measured chromaticity coordinate for the NaBaBO3:Tm3+phosphor under 359 nm excitation is determined to be (0.1470, 0.1090). The present work suggests that the NaBaBO3:Tm3+,K+ phosphor is a promising blue-emitting material for NUV white light-emitting diodes.