First-principles study of fundamental properties and electronic structure of alloys

We have performed first-principles calculations using full-potential augmented-plane-wave method to investigate the fundamental properties of the Cd_1–xZn_xTe alloys. The composition dependence of the lattice constant and the bulk modulus have been estimated from total energy calculations. By means of the analytical fitting the band structures in the vicinity of the Brillouin center a complete set of effective electron- and hole-masses have also been derived. In order to further understand the effects of the chemical bonding on the above macroscopic properties we then studied the relaxation behaviors and the changes of the electronic states upon alloying for x=0.25 system. The results presented here yield a general understanding of the fundamental properties for the Cd_1–xZn_xTe crystals studies.     

3D ordered macro-/mesoporous Ni_xCo_(100-x) alloys as high-performance bifunctional electrocatalysts for overall water splitting

Electrochemical water splitting is a facile and effective route to generate pure hydrogen and oxygen.However,the sluggish kinetics of hydrogen evolution reaction(HER) and especially oxygen evolution reaction(OER) hinder the water splitting efficiency.Meanwhile,the high-cost of noble-metal catalysts limit their actual application.It is thus highly urgent to exploit an economical and earthabundant bifunctional HER and OER electrocatalyst to simplify procedure and reduce cost.Herein,we synthesize the three-dimensionally ordered macro-/mesoporous(3 DOM/m) Ni_xCo_(100-x) alloys with distinctive structure and large surface area via a dual-templating technique.Among them,the3 DOM/m Ni_(61)Co_(39) shows the lowest overpotentials of 121 mV and 241 mV at 10 mA/cm~2 for HER and OER,respectively.Furthermore,when employed for water splitting,the Ni_(61)Co_(39) only requires 1.60 V to approach 10 mA/cm2 and presents excellent stability.These encouraging performances of the Ni_(61)Co_(39)render it a promising bifunctional catalyst for overall water splitting.     

Development of Surface Nano-Crystallization in Alloys by Surface Mechanical Attrition Treatment (SMAT)

Nanometer-sized grain structures that exhibit a large number of grain boundaries on the surface of a bulk material demonstrate excellent properties relative to their coarse-grained (CG) equivalents. Surface modification using surface mechanical attrition treatment (SMAT) is an option that cab be used to tailor the corrosion, tribological, mechanical, and chemical reaction properties of a surface. SMAT is an effective route to create the nanostructured surface layer. The SMAT process has unique advantages compared with the other coating and deposition techniques for surface nanocrystallization. For example, SMAT does not alter the chemical composition of the nanocrystalline surface layer in the matrix. In addition, SMAT has been demonstrated to activate the material surface layer by surface modification and enhance the atomic diffusivity. This article presents a review of the advantages offered by the SMAT technique for the creation of high performance surface layers. The influence of the created nanocrystalline layer on mechanical, physical, and chemical properties is assessed. Developments and the current status of the surface nanolayer that are formed are evaluated from a physical approach. Finally, prospects for the future development of grain refinement on the surface of a material matrix and potential applications are presented.     

Electron irradiation-enhanced core/shell organization of Al(Cr,Fe, Mn)Si dispersoids in Al–Mg–Si alloys

The age hardening 6061-T6 aluminium alloy has been chosen as structural material for the core vessel of the material testing Jules Horowitz nuclear reactor. The alloy contains incoherent Al(Cr, Fe, Mn)Si dispersoids whose characterization by energy-filtered transmission electron microscopy (EFTEM) analysis shows a core/shell organization tendency where the core is (Mn, Fe) rich, and the shell is Cr rich. The present work studies the stability of this organization under irradiation. TEM characterization on the same particles, before and after 1 MeV electron irradiation, reveals that the core/shell organization is enhanced after irradiation. It is proposed that the high level of point defects, created by irradiation, ensures a radiation-enhanced diffusion process favourable to the unmixing forces between (Fe, Mn) and Cr. Shell formation may result in the low-energy interface segregation of Cr atoms within the (Fe, Mn) system combined with the unmixing of Cr, Fe and Mn components.     

Tb doping induced enhancement of anomalous Hall effect in NiFe films

Tbx(Ni0.8Fe0.2)1-x films with x≤0.14 are fabricated and the anomalous Hall effect is studied.The intrinsic anomalous Hall conductivity and the extrinsic one from the impurity and phonon induced scattering both increase with increasing x.The enhancement of the intrinsic anomalous Hall conductivity is ascribed to both the weak spin–orbit coupling enhancement and the Fermi level shift.The enhancement of the extrinsic term comes from the changes of both Fermi level and impurity distribution.In contrast,the in-plane and the out-of-plane uniaxial anisotropies in the Tb Ni Fe films change little with x.The enhancement of the Hall angle by Tb doping is helpful for practical applications of the Hall devices.     

硫脲络合–火焰原子吸收光谱法测定低硅铝合金中的银含量

采用硫脲络合–火焰原子吸收光谱法测定低硅铝合金中的银元素含量。实验探讨了酸度及硫脲用量对银测定的影响及铝合金中基体元素与共存元素对银元素分析线的干扰情况。结果表明:选用9%的盐酸和3%的硝酸溶解试样最好,加入5 mL 50 g/L硫脲溶液可消除氯离子对试验结果的影响,基体铝元素和其它共存元素不干扰银的测定。根据低硅铝合金中银元素的含量范围,合成系列标准溶液,建立工作曲线,工作曲线的线性范围为0.05%~0.50%。银元素含量为0.30%的样品测定结果的相对标准偏差为0.15%(n=8),标准加入回收率为96.8%~98.5%。该方法操作简便、重现性好、测量结果准确可靠。     

Molecular dynamic study of temperature dependence of mechanical properties and plastic inception of CoCrCuFeNi high-entropy alloy

Molecular dynamics simulations are performed to study mechanical characteristics and homogeneous plastic inception of CoCrCuFeNi high-entropy alloy at various temperatures under uniaxial tension. It is found that the elastic modulus and ultimate tensile strength increase with temperature decreasing. A notable softening effect is observed at the elastic deformation stage caused by the decrease of the interatomic force gradient. Extrinsic stacking faults and deformation twins are extensively observed, which are formed via intrinsic stacking faults overlap.