B_2-NiAl弹性性质Ag合金化效应的理论研究

采用第一原理赝势平面波方法和基于虚拟晶体势函数近似(VCA),计算了Ag合金化(浓度x<1.0%,原子分数,下同)时完整与缺陷B2-NiAl晶体的弹性性质,并采用弹性常数C44,Cauchy压力参数(C12-C44)、弹性模量E、剪切模量G及其与体模量B0的比值G/B0等,表征和评判了Ag合金化浓度x对NiAl金属间化合物延性与硬度的影响。结果表明:无论是无缺陷的理想NiAl晶体,还是含Ni空位或Ni反位的NiAl缺陷晶体,x<1%的Ag合金化均可使其硬度大幅提高;在0%～0.6%以及0.7%～1%区间,Ag将提高NiAl完整晶体材料的延性,并且以0.6%附近为最好;当x≤0.5%时,Ag合金化能改善Ni空位的NiAl多晶材料延性,并以x=0.32%～0.48%时,Ni空位的NiAl多晶延性的提升幅度尤为明显;而当1%>x>0.5%时,却可明显提高Ni反位B2-NiAl晶体的延展性,并在x=0.73%～1%区间呈现相对较好的韧化效果。上述结论归于低浓度Ag的固溶强化与高浓度Ag的富Ag相软化作用。

Ag微合金化对Al-Mg-Si合金析出相结构的影响

采用第一性原理计算和球差矫正透射电子显微分析,从形成焓、电荷密度和原子尺度微观结构等方面对Al-Mg-Si-Ag合金的析出相结构进行研究。结果表明,Ag微合金化后β″相的稳定性降低,Ag原子倾向于偏聚在β″相/基体界面处,这主要是由于Ag对电子的攫取作用;Ag微合金化后形成的β′相结构更为稳定,Ag原子能够进入β′相内部占据其Si1和Si2位置,且形成焓均低于β″相,促进β″相转变为β′相,这与Ag-Al原子间的强共价键有关;Ag微合金化对β相的结构稳定性不利,这主要是Ag-Mg原子间的弱键强导致的。

Microstructure and mechanical properties of extruded Mg-8.5Gd-2.3Y-1.8Ag-0.4Zr alloy

The microstructure, age hardening behavior and mechanical properties of an Mg-8.5Gd-2.3Y-1.8Ag-0.4Zr alloy prepared by casting and hot extrusion techniques were investigated. The solution-treated （T4 temper） alloys were extruded at 400, 450 and 500 °C with an extrusion ratio of 10：1, respectively. Optimized mechanical properties were obtained by extrusion at 400 °C followed by T5 treatment under the combined effects of grain refinement and precipitation strengthening. The alloy exhibits a grain size of about 5.0 μm, initial and peak microhardness of HV 109 and HV 129, respectively. The tensile yield strength, ultimate tensile strength and elongation at room temperature are 391 MPa, 430 MPa and 5.2%, respectively.

Ag-Ni alloy nanoparticles for electrocatalytic reduction of benzyl chloride

Ag-based nanocatalysts exhibit good catalytic activity for the electrochemical reduction of organic halides. Ag-Ni alloy nanoparticles（NPs） were facilely prepared by chemical reduction, and the as-prepared nanocatalysts were characterized by X-ray diffraction, ultraviolet-visible spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The electrocatalytic activity of Ag-Ni NPs for benzyl chloride reduction was studied in organic medium using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results show that the addition of Ni element can obviously decrease the size of Ag-Ni NPs, shift the reduction peak potential（φp） of benzyl chloride positively, and increase the catalytic activity of Ag-Ni NPs. However, when the Ni content reaches a certain value, the catalytic activity of Ag-Ni NPs decreases. Meanwhile, the synergistic catalytic effect of Ag-Ni NPs was also discussed.

Mechanical alloying and subsequent heat treatment of Ag-Zn powders

Microstructural evolution during mechanical alloying of Ag and Zn, and subsequent heat treatments were investigated. The mechanical alloying was carried out in a SPEX 8000D miller. The microstructural characterization was obtained by X-ray diffraction （XRD）, transmission electron microscopy （TEM） and scanning electron microscopy （SEM）. The thermal behavior was studied using differential scanning calorimetry （DSC）. Based on the results obtained, it can be concluded that at the early stages of milling was possible to detect the ε, β, β′, α solid solutions and remaining Zn. Later, the ε, β, β′ and Zn phases disappeared while the Zn concentration of the α solid solution was strongly increased. After 7.2 ks of milling, the mechanical alloying process reached a steady state. During this period, both the composition and crystallite size of the α solid solution remained practically unchanged. On the other hand, subsequent heat treatments of milled powders showed that the α solid solution could also be obtained by the combination of mechanical alloying and heat treatment. Finally, the evolution of the microstructure during milling and annealing was combined to propose an optimal processing route in order to obtain a α solid solution.

Low temperature synthesis and thermal properties of Ag-Cu alloy nanoparticles

Ag-Cu alloy nanoparticles were synthesized by simple low temperature chemical reduction method using metal salts（acetate/sulphates） in aqueous solution with sodium borohydride as reducing agent.The chemical reduction was carried out in the presence of nitrogen gas in order to prevent the oxidation of copper during the reaction process.The alloy nanoparticles were characterized by XRD,UV-Vis,particle size analysis,EDS,TG-DTA and SEM analysis.From the XRD analysis,the crystallite sizes of the prepared samples were calculated using Scherrer formula and the values were found to be in the range of 15 nm.UV-Vis studies conform the formation of alloy nanoparticles.EDS analysis shows the presence of silver and copper in the samples.The SEM observation reveals that the samples consist of grains with average grain size up to 40 nm,and the particle size dependant melting point was studied by TG-DTA.

Effects of trace Ag on precipitation behavior and mechanical properties of extruded Mg−Gd−Y−Zr alloys

The effects of trace Ag element on the precipitation behaviors and mechanical properties of the Mg−7.5Gd−1.5Y−0.4Zr(wt.%)alloy by means of tensile test,X-ray diffractometry,scanning electron microscopy,electron backscattered diffractometry,and scanning transmission electron microscopy.There is an unusual texture(á0001ñ//extrusion direction)in the extruded Mg−Gd−Y−Zr alloys containing 0.5 wt.%Ag.During the aging periods at 225℃,the addition of the trace Ag does not form new precipitates,just accelerates aging kinetics,and refinesβ′precipitates,thereby increasing the number density of theβ′precipitates by Ag-clusters.Moreover,the Mg−Gd−Y−Zr alloy containing 0.5 wt.%Ag shows the most excellent synergy of strength and plasticity(408 MPa of ultimate tensile strength,265 MPa of yield strength,and 12.9%of elongation to failure)after peak-aging.

Corrosion behavior of bulk two-phase Ag-25Cu alloys with different microstructures in NaCl aqueous solution

In order to have a better understanding on the corrosion mechanisms of bulk two-phase Ag-25Cu (at.%) alloys with different microstructures, two bulk nanocrystalline Ag-25Cu alloys and one coarse grained counterpart were prepared by liquid phase reduction (LPR), mechanical alloying (MA) and powder metallurgy (PM) methods, respectively. Their corrosion behavior was investigated comparatively using electrochemical methods in NaCl aqueous solution. Results show that the microstructure of the coarse grained PMAg-25Cu alloy is extremely inhomogeneous. On the contrary, compared with PMAg-25Cu alloy, the microstructures of the nanocrystalline LPRAg-25Cu and MAAg-25Cu alloys are more homogeneous, especially for LPRAg-25Cu alloy. The corrosion rate of MAAg-25Cu alloy is higher than that of PMAg-25Cu alloy, but lower than that of LPRAg-25Cu alloy. Furthermore, the passive films formed by three Ag-25Cu alloys exhibit n-type semiconducting properties. The passive current density of LPRAg-25Cu alloy is lower than that of PMAg-25Cu alloy, but higher that of MAAg-25Cu alloy.