Applied Mechanics and Materials Vols. 275-277

Abstract: Al-Fe-Ni ternary powder mixtures containing (FeAl)-40(60) at.% Ni and (FeAl3)-10(30) at.% Ni were mechanically alloyed by a high-energry planetary ball mill. The structural evolution of the powders during milling was studied by X-ray diffraction technique (XRD). During milling of (FeAl)-40(60) at.% Ni system, Al and Fe solid solutions formed at the early stage change to FeAl, AlNi3 and FeNi3 intermetallic compounds. However, the Al and Fe solid solutions observed at the early stage transform into Al3Ni2, AlFe3 and AlFe0.23Ni0.77 intermetallic compound at last. The experimental results showed that the last milling products were decided by the proportion of atom between Al and Fe in the powder and the Ni content in the power had not affected to the last products.

Abstract: Flower-like, sphere and lamellar structures of copper sulfide have been prepared by an electrochemical method with PAM hydrogel as template. The unique synthetic method required no multiple growth steps typical of other methods, and just utilized the electric currents to drive the ions to realize the controlling the resultant morphology in the PAM hydrogel system. The structure of product was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The morphology of these structures could be controlled by adjusting the content of PAM in hydrogel, and the intension of electric current.

Abstract: Ag nanoparticle functionalized TiO₂ nanowire (TiO₂ NW @ Ag NP) was synthesized and the gas sensing properties of the nanowire film was investigated. The size and the distribution density of Ag nanoparticles can be easily controlled. The sensor based on Ag nanoparticle functionalized TiO2 nanowire thin film has promising sensing properties, and at room temperature, its sensitivity towards H₂ and O₂ can reach 500 ppm and 1000 ppm respectively.

Abstract: Through stress-controlled fatigue testing under different stress amplitudes, effects of stress amplitude on the fatigue life and crack propagation mechanism of the extruded Mg-3Al-2Sc alloy were investigated. The results show that, within the stress range of 13.5~82.5 MPa and stress ratio of 0.2, the fatigue life of the alloy decreases and growth rate of fatigue crack increases with increasing stress amplitude. Cleavage fracture mode dominates the crack initiation area and stable crack propagation area. For the final rapid fracture area, the fatigue fracture is combined mode of semi-cleavage and cleavage as well as intercrystalline fracture.

Abstract: A Johnson-Mehl-Avrami-Kolmogorov (JMAK)-model was established for dynamic recrystallization in hot deformation process of 52100 steel. The effects of hot deformation temperature, true strain and strain rate on the microstructural evolution of the steel were physically studied by using Gleeble-1500 thermo-mechanical simulator and the experimental results were used for validation of the JMAK-model. Through simulation and experiment, it is found that the predicted results of DRX volume fraction, DRX grain size and average grain size are in good agreement with the experimental ones.

Abstract: We investigated the atomic rich and defect effects on the half-metallicity of the full-Heusler alloy Co₂MnGe from the first principles. Our results show that both Mn-rich and Co-rich could increase the tunnel magnetoresistance (TMR) of the Co₂MnGe/MgO magnetic tunnel junctions (MTJs). As for defect, all of investigated Co, Mn and Ge defect show that the spin polarization at E_f and the TMR in the MTJs with Co and Mn defect is significatively decreased except for Ge-defected MTJs.

Abstract: A series of warm tensile tests for B349/590DP steel are performed at the stain rates of 0.0004/s, 0.001/s, 0.01/s and 0.08/s in this paper. From the test data, it is found that the effect of temperature and strain rate on material’s deformation behaviors is opposite to that of other temperature ranges. And with the change of strain rate and temperature, the relations between the material parameters such as the work-hardening exponent n, the stress hardening coefficient K and forming process conditions becomes uncertain. Moreover, authors investigated the reasons for above phenomena. Research results demonstrate that it is very necessary to appropriately optimize the warm forming process scheme and strictly control the warm forming process parameters so that both the formability and safety performance are considered simultaneously.

Abstract: The influence of RE on corrosion rust layer of low carbon steel in CSP in a simulated coastal-industrial atmosphere was investigated by weight loss, SEM, XRD, and electrochemical measurements. The results demonstrate that the corrosion rate of low carbon steel in CSP with RE is higher at the initial stage and then lower in the late stage than that of samples without RE, which is caused by the formation of a compact and continuous rust layer with the addition of RE. The relative content of α-FeOOH and Fe3O4 in rust increased in the low carbon steel with RE indicates an improved protective ability of the rust. Using the analysis of resistance, the EIS results also indicate that the enhancement of protective ability of the rust layer by the RE is the main reason for increasing corrosion resistance of low carbon in CSP in simulated coastal atmosphere.

Abstract: The isothermal constant strain rate tensile tests of the TC21 titanium alloy were conducted by SSAN-CMT4104 electronic tensile testing machine at different temperature. After superplastic deformation, the alloy was treated with double annealing heat treatment, and microstructure of the alloy was analyzed. The results show that dynamically recrystallization occurs during the superplastic tensile deformation. The primary α-grains aggregated and merged to form new crystal grains with irregular grain boundaries. The amount and morphology of primary α phase change gradually with the increasing of temperature. The alloy has duplex microstructure composed of primary α phase and different forms of β-transformed structure after superplastic deformation and double annealing. At deformation temperature of 930°C, the basket weave structure with equiaxed α phase appears.

Abstract: Uniaxial tensile tests were conducted on high strength steel 600 (HS600) in Split-Hopkinson Tension Bar at different strain rates in the range of 1100 to 3200s^-1and in electromechanical universal testing machine at the strain rate of 1.1×10-3s^-1. Digital image correlation was used together with high-speed photography to obtain full-field displacement and strain in the tensile specimens at dynamic strain rate tests. This high strength steel shows significant strain rate sensitivity. Based on the experimental results, the material parameters of Johnson-Cook model are determined. This model fits the experimental data well in the plastic zone.