Showing papers by "H.F. Zhang published in 2015"

Atomic interaction mechanism for designing the interface of W/Zr-based bulk metallic glass composites

Abstract: The interaction between active element Zr and W damages the W fibers and the interface and decreases the mechanical properties, especially the tensile strength of the W fibers reinforced Zr-based bulk metallic glass composites (BMGCs). From the viewpoint of atomic interaction, the W-Zr interaction can be restrained by adding minor elements that have stronger interaction with W into the alloy. The calculation about atomic interaction energy indicates that Ta and Nb preferred to segregate on the W substrate surface. Sessile drop experiment proves the prediction and corresponding in-situ coating appears at the interface. Besides, the atomic interaction mechanism was proven to be effective in many other systems by the sessile drop technique. Considering the interfacial morphology, Nb was added into the alloy to fabricate W/Zr-based BMGCs. As expected, the Nb addition effectively suppressed the W-Zr reaction and damage to W fibers. Both the compressive and tensile properties are improved obviously.

Collisionless shocks driven by 800 nm laser pulses generate high-energy carbon ions

Abstract: We present experimental studies on ion acceleration from diamond-like carbon (DLC) foils irradiated by 800 nm, linearly polarized laser pulses with peak intensity of 17 × 1019 W/cm2 to 35 × 1019 W/cm2 at oblique incidence Diamond-like carbon foils are heated by the prepulse of a high-contrast laser pulse and expand to form plasmas of near-critical density caused by thermal effect before the arrival of the main pulse It is demonstrated that carbon ions are accelerated by a collisionless shock wave in slightly overdense plasma excited by forward-moving hot electrons generated by the main pulse

Experimental study on the electrical conductivity of quartz andesite at high temperature and high pressure: evidence of grain boundary transport

Abstract: . In this study, the electrical conductivity of quartz andesite was measured in situ under conditions of 0.5–2.0 GPa and 723–973 K using a YJ-3000t multi-anvil press and a Solartron-1260 Impedance/Gain-Phase Analyzer. Experimental results indicate that grain interior transport controls the higher frequencies (102–106 Hz), whereas the grain boundary process dominates the lower frequencies (10−1–102 Hz). For a given pressure and temperature range, the relationship between Log σ and T−1 follows the Arrhenius relation. As temperature increased, both the grain boundary and grain interior conductivities of quartz andesite increased; however, with increasing pressure, both the grain boundary and grain interior conductivities of the sample decreased. By the virtue of the dependence of grain boundary conductivity on pressure, the activation enthalpy and the activation volume were calculated to be 0.87–0.92 eV and 0.56 ± 0.52 cm3 mol−1, respectively. The small polaron conduction mechanism for grain interior process and the ion conduction mechanism for grain boundary process are also discussed.

Microstructures and mechanical property of AlCoNiCrFe alloy annealed in high magnetic field

Abstract: A rapidly solidified high entropy alloy AlCoNiCrFe was annealed at different temperatures with high magnetic field applied up to 4 T. Both precipitation and coarsening of the precipitates were promoted during annealing in a high magnetic field, and nanosized arrayed particles as well as boundary oriented secondary phases were formed with effects of magnetic field. The microstructural features were obtained owing to enhancement of atomic diffusion by applying high magnetic field. It was found that both hardness and yield strength were not strongly dependent on the magnetic field, but the ultimate compression strength is reduced as higher magnetic field is applied due to formation and coarsening of the precipitates on grain boundaries.

The influence of different preparation methods on the microstructures and properties of the in situ bulk-metallic-glass-matrix composites

Abstract: In this work, the effects of different preparation methods on the microstructures and properties of the Ti45.7Zr33Ni3Cu5.8Be12.5 alloy were systematically studied by both experimental and numerical ways. It is found that the heating methods and the cooling rate during the process of preparation have great influences not only on the morphology and crystalline structure of the solid solutions but also on the thermal stability of the amorphous phase. Furthermore, the different crystalline structures and micromorphologies of the ductile phase will also influence the mechanical properties. And the uniaxial compression tests at room temperature verify that the Ti45.7Zr33Ni3Cu5.8Be12.5 samples obtained by different preparation methods possess different degrees of plasticity. The better comprehensive properties were found for samples with a larger size under the copper mold cooling conditions. The variation of the morphology of the solid solution phase under different preparation conditions is believed to be the vital factor that leads to the diversity in properties.

Micro-mechanical behavior of porous tungsten/Zr-based metallic glass composite under cyclic compression

Abstract: The micro-mechanical behavior of porous tungsten/Zr-based metallic glass composites with different tungsten volume fraction was investigated under cyclic compression by synchrotron-based in - situ high-energy X-ray diffraction (HEXRD) and finite element modeling (FEM). During cyclic compression, the dislocation in the tungsten phase tangled near the interfaces, indicating that the elastic metallic glass phase restricted dislocation motion and obstructed the deformation of the tungsten phase because of the heterogeneity in stress. After the metallic glass phase yielded, the dislocation tended to propagate away from the interfaces, showing the decrease of the interphase stress affected the direction of motion in the dislocations. The tungsten phase exhibited increased yield strength with the increase of cyclic loading number. Yield stress of the tungsten phase decreased with increasing the tungsten volume fraction during cyclic compression, which was influenced by the elastic strain mismatch between the two phases. The stress heterogeneity and the stress distribution difference between the two phases resulted in that the yield strength of the metallic glass phase decreased with the increase of tungsten volume fraction, and accelerated the formation of shear bands in the metallic glass phase as well as cracks in the tungsten phase. The heterogeneity in stress also excessed the interface bonding strength, inducing interface fracture near interfaces.

Mechanical response of Ti-based bulk metallic glass under static and dynamic indentations

Abstract: Vickers hardness and plastic deformation of Ti-based bulk metallic glass (Ti-BMG) were investigated under both static and dynamic indentations. Dynamic hardness is obviously greater than that under static indentation, which is attributed to the combination effects of energy barriers and separation of nanocrystallizations from the metallic glass during dynamic indentation. Although dynamic indentation induced more severe deformation than that under static indentation, the deformation characteristics in the two loading cases are nearly the same: both exhibiting semi-circular shear bands on the top surface and a mixture of semi-circular and radial shear bands underneath the indentation tips. The most obvious difference between the two kinds of indentations is that substantial successive shear bands accompanied by numerous shear-offsets formed in dynamic indentation while obviously less shear bands and shear-offsets formed in static indentation.