Study on Nanocrystalline Rare Earth Mg-Based System Hydrogen Storage Alloys with AB_3-Type

A sort of rare earth Mg-based system hydrogen storage alloys with AB3-type was prepared by double-roller rapid quenching method. The alloys were nanocrystalline multi-phase structures composed of LaNi3 phase and LaNi5 phase by X-ray diffraction and scanning electron microscopy analyses, and the suitable absorption/desorption plateau was revealed by the measurement of P-C-I curve. Electrochemical studies indicate that the alloys exhibit good electrochemical properties such as high capacity and stable cycle life, and the discharge capacity is 369 mAh·g-1 at 0.2 C (72 mA·g-1). after 460 cycles, the capacity decay was only 19.4% at 2 C (720 mA·g-1).

Phase formation with NaZn_(13) structure in metamagnetic La(Fe_(1–x)Co_x)_(11.9)Si_(1.1) compounds

The effects of different annealing conditions on the phase formation with NaZn13 structure were investigated in La（Fe1-xCox）11.9Si1.1 （x=0.068） compounds. It was found that the 1：13 phase was not formed directly from the melt upon cooling but via a peritectic reaction between the pro-peritectic γ-Fe and the La-rich phase. Annealing temperature was very important for the formation of 1：13 phase. Ice water was confirmed to be a preferable quenching medium. La（Fe1-xCox）11.9Si1.1 （x=0.068） compounds with almost single 1：13 phase were obtained at 1473 K after 15 d.

Effect of the potential function and strain rate on mechanical behavior of the single crystal Ni-based alloys:A molecular dynamics study

Molecular dynamics has been widely used to study the fundamental mechanism of Ni-based superalloys.However,the effect of the potential function and strain rate on mechanical behavior has rarely been mentioned in the previous molecular dynamics studies.In the present work,we show that the potential function of molecular dynamics can dramatically influence the simulation results of single crystal Ni-based superalloys.The microstructure and mechanical behavior of single crystal Ni-based superalloys under four commonly used potential functions are systematically compared.A most suitable potential function for the mechanical deformation is critically selected,and based on it,the role of strain rate on the mechanical deformation is investigated.

Efficiency of Chalcone Compounds Inhibitors for Acid Corrosion of Al and Al-3.5Mg Alloy

Corrosion inhibition of Al and Al-3.5Mg alloy by organic compounds, namely chalcones in hydrochloric acid solutions has been investigated by rapid polarization technique and weight loss method. Polarization measurements show that, the inhibitors act cathodically both in case of Al and Al-3.5Mg alloy. It was found from the weight loss measurements that, the inhibition efficiency depends on the substituent in the chalcone compound. The relative inhibitive efficiency of these compounds has been explained on the basis of structure dependent electron donor properties of the inhibitors and the metal inhibitor interaction on the surface. The inhibition efficiency ranges from 16 to 64% for Al and from 30% to 91% for Al-3.5Mg alloy

Electronic Structure Effect on Model Cluster for L1_2 Structure of Al_3Ti Intermetallic Compound with an Addition of Alloying Elements Fe, Ni and Cu

By use of self-consistent field Xα scattered-wave (SCF-Xα-SW) method, the electronic structure was calculated for four models of Ti4Al14X (X=Al, Fe, Ni and Cu) clusters. The Ti4Al14X cluster was developed based on L12 Al3Ti-base intermetallic compound. The results are presented using the density of states (DOS) and one-electron properties, such as relative binding tendency between the atom and the model cluster, and hybrid bonding tendency between the alloying element and the host atoms. By comparing the four models of Ti4Al14X cluster, the effect of the Fe, Ni or Cu atom on the physical properties of Al3Ti-based L12 intermetallic compounds is analyzed. The results indicate that the addition of the Fe, Ni or Cu atom intensifies the relative binding tendency between Ti atom and Ti4Al14X cluster. It was found that the Fermi level (EF) lies in a maximum in the DOS for Ti4Al14Al cluster; on the contrary, the EF comes near a minimum tn the DOS for Ti4Al14X (X=Fe, Ni and Cu) cluster. Thus the L12 crystal structure for binary Al3Ti alloy is unstable, and the addition of the Fe, Ni or Cu atom to Al3Ti is benefical to stabilize L12 crystal structure. The calculation also shows that the Fe, Ni or Cu atom strengthens the hybrid bonding tendency between the central atom and the host atoms for Ti4Al14X cluster and thereby may lead to the constriction of the lattice of Al3Ti-base intermetallic compounds.

Microstructure and phase forming process of Al-3Ti-0.2C-1RE grain refiner

An Al-3Ti-0.2C-1RE grain refiner was prepared by in-situ reaction method.The microstructure was investigated by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy-dispersive spectrometry(EDS) and X-ray diffraction(XRD).The results show that the Al-3Ti-0.2C-1RE grain refiner is composed of α-Al,TiAl3,TiC and Ti2 Al20 Ce phases.Compared with Al-3Ti-0.2C refiner,the morphology of TiAl3 phase is changed and Ti2 Al20 Ce phases form with the addition of RE.Accordingly,the refining performance is improved.The phase forming process of the refiner is as follows: Blocky Ti2 Al20 Ce and fine blocky TiAl3 form in the melt at the initial stage of reaction,then the fine blocky TiAl3 gradually disappears,and the blocky Ti2 Al20 Ce grows bigger with the increase of holding time.The predominant mechanism to synthesize TiC particles is the reaction between high concentration of solute Ti atoms and graphite particles.

Structure and Magnetic Properties of Fe1-xCx Solid Solution Prepared by Mechanical Alloying

Supersaturated solid solutions Fe1-xCx （0≤x≤0.9 ） of wide composition range have been prepared by mechanical alloying process. Nanocrystalline phase was formed for 0 ≤ x ≤ 0.67 and a large grain phase for 0.75 ≤ x ≤ 0.9. The large fraction of graphite volume puts off formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows simple magnetic dilution, and eoereivity He is mainly due to dissolution of carbon at grain boundaries. In the nanocrystalline phase the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for x ≤ 0.5, suggesting that the high carbon concentration may enhance diffusion of carbon into the Fe lattice. It shows a discontinuity in the Hc variation with a grain size D of nanocrystalline phase. For small grain D below the critical value, Hc increases with D. For a large grain D, Hc decreases with increasing D. The solubility limit of carbon in a-Fe extended by nanocry- stalline phase formation is discussed.

Phase relationships in the Yb-Fe-Sb system at 530 ℃

Phase relationships in the Yb-Fe-Sb ternary system at 530 °C were investigated mainly by powder metallurgy and X-ray powder diffraction.Nine binary compounds（Yb6Fe23, Yb2Fe17, FeSb, FeSb2, YbSb2, YbSb, Yb11Sb10, Yb4Sb3, and αYb5Sb3） and one ternary compound（Fe4YbSb12） were confirmed in this system at 530 °C.The homogeneity range of FeSb phase extended from approximately 43at.%Sb to 45at.%Sb, the maximum solid solubility of Sb in Fe phase and Yb in FeSb phase was approximately 3at.%Sb and 1at.%Yb at 530 °C, respectively.Isothermal section of the phase diagram of the Yb-Fe-Sb ternary system at 530 °C consisted of thirteen single-phase regions, twenty-four two-phase regions, and twelve three-phase regions.

Antimony-based intermetallic compounds for lithium-ion and sodium-ion batteries:synthesis,construction and application

The development of alternative electrode materials with high energy densities and power densities for batteries has been actively pursued to satisfy the power demands for electronic devices and hybrid electric vehicles. Recently, antimony（Sb）-based intermetallic compounds have attracted considerable research interests as new candidate anode materials for high-performance lithium-ion batteries（LIBs） and sodium-ion batteries（SIBs） due to their high theoretical capacity and suitable operating voltage. However, these intermetallic systems undergo large volume change during charge and discharge processes, which prohibits them from practical application. The rational construction of advanced anode with unique structures has been proved to be an effective approach to enhance its electrochemical performance. This review highlights the recent progress in improving and understanding the electrochemical performances of various Sb-based intermetallic compound anodes. The developments of synthesis and construction of Sb-based intermetallic compounds are systematically summarized. The electrochemical performances of various Sb-based intermetallic compound anodes are compared in its typical applications（LIBs or SIBs）.

First-principles Calculations of Strengthening Compounds in Magnesium Alloy： A General Review

First-principles computation methods play an important role in developing and designing new magnesium alloys.In this article,we present an overview of the first-principles modeling techniques used in recent years to simulate ideal models of the structure of strengthening compounds in Mg alloys.For typical Mg compounds,structural stability,mechanical properties,electronic structure and thermodynamic properties have been discussed.Specifically,the elastic anisotropies of these compounds are examined,which is highly correlated with the possibility of inducing micro-cracks.Furthermore,some heterogeneous nucleation interfaces investigated by first-principles method are reviewed.Some of the theoretical results are compared with available experimental observations.We hope to illustrate that the first-principles computation can help to accelerate the design of new Mg-based materials and the development of materials genome initiative.Remaining problems and future directions in this research field are considered.

Diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couples

The diffusion behavior and reactions between AI and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al2Ca is the only phase existing in the diffusion reaction layers. The volume fraction of Al2Ca in diffusion reaction layers increases linearly with temperature. The standard enthalpy of formation for intermetallic compounds was rationalized on the basis of the Miedema model. Al-Ca intermetallic compounds were preferable to form in the Mg-Al-Ca ternary system under the same conditions. Over the range of 350-400℃, the structure of Al2Ca is more stable than that of Al4Ca, Al14Ca13and Al3Ca8, The growth constants of the layer I, layer II and entire diffusion reaction layers were determined. The activation energies for the growth of the layer I, layer II and entire diffusion reaction layers were （80.74 ± 3.01 ） kJ/mol, （93.45 ±2.12） kJ/mol and （83.52 ±1.50） kJ/mot, respectively. In layer I and II, AI has higher integrated interdiffusion coefficients D^i^Int,layer layer than Ca. The average effective interdiffusion coefficients D^Al^eff values are higher than D^Ca^eff in the layer I and II.

Highly nonlinear property and threshold voltage of Sc_2O_3 doped ZnO-Bi_2O_3-based varistor ceramics

A series of ZnO-Bi2O3-based varistor ceramics doped with 0-0.4 mol.% Sc2O3 were prepared by high-energy ball milling and sintered at temperatures between 1000 and 1150oC. X-ray diffractometry （XRD） and scanning electron microscopy （SEM） were applied to characterize the phases and microstructure of the varistor ceramics. A DC parameter instrument for varistor ceramics was applied to investigate the electronic properties and V-I characteristics. The results showed that there were no changes in crystal structure with Sc2O3-doped varistor ceramics and that the average size of ZnO grain increased first and then decreased. The best electronic characteristics of the varistor ceramics prepared by high-energy ball milling were found in 0.3 mol.% Sc2O3-doped ZnO-Bi2O3 -based ceramics sintered at 1000 oC, which exhibited a threshold voltage of 821 V/mm, nonlinear coefficient of 62.1 and leakage current of 0.16 μA.

Microstructure and electrical resistivity in the GdNi_(5–x)Cu_x intermetallic series

The effect of the Ni/Cu substitution on the electrical resistivity and microstructure of the polycrystalline GdNi5-xCux series was studied. The value of temperature of phase transition（T_（ph）） estimated from temperature dependence of electrical resistance varied non-linearly across copper doping from 32.5 K（x=0.0） to 29.1 K（x=5.0）. The value of residual resistivity（ρo） estimated at low temperature range decreased from 27.28 μΩcm（x=0.0） to 9.44 μΩcm（x=5.0）, which was discussed as the influence of microstructure. In order to describe the temperature dependence of resistivity ρ（T） a variety of approaches were applied due to different scattering mechanisms occurring at high and low temperature ranges. The change within ρ（T） curvature was evidenced at low temperature range across copper doping. The temperature variation of the resistivity was quite peculiar for Cu-rich compounds（x=4.8, x=5.0）, which might be correlated with the incommensurate magnetic structure derived from the weakly negative interaction between the nearest neighbours of Gd. The correlation between microstructure and resistivity was observed.

Effect of Al_(82.8)Cu_(17)Fe_(0.2) alloy doping on structure and magnetic properties of SmCo5-based ribbons

This work tries to improve the magnetic properties by multi-element doping in the form of a ternary alloy.SmCo_(5+)χwt%Al-Cu-Fe(x=0-7)ribbons melt-spun at 40 m/s were produced by adding Al_(82.8)Cu_(17)Fe_(0.2)alloy into SmCo_(5) matrix,and their phases,microstructure,and magnetic properties were investigated.The results show that both x=0 and 3 ribbons form a cellular microstructure.Al-Cu-Fe addition reduces the content of the Sm_(2)(Co,M)_(7) cell wall,narrows its width,and forms the local disordered micro-regions and solute-segregation nanoclusters in the Sm(Co,M)_(5) grains.With x increasing to5,Al-Cu-Fe addition promotes the phase separation between and within grains of the SmCo_(5)-based alloy.The Al-Cu-Fe addition can simultaneously improve the coercivity and magnetization of the SmCo_(5)-based ribbons,in particular,the magnetization of the x=3 ribbons increases by 35%,while the coercivity of the x=5 ribbons increases by 3.9 times.Finally,the microstructure evolution models are built up,and the relationship between the microstructure and the magnetic properties is discussed.

Multiple radial phosphorus segregations in GaAsP core-shell nanowires

Highly faceted geometries such as nanowires are prone toform self-formed features,especially those that are driven by segregation.Understanding these features is important in preventing their formation,understanding their effects on nanowire properties,or engineering them for applications.Single elemental segregation lines that run along the radii of the hexagonal cross-section have been a common observation in alloy semiconductor nanowires.Here,in GaAsP nanowires,two additional P rich bands are formed on either side of the primary band,resulting in a total of three segregation bands in the vicinity of three of the alternating radii.These bands are less intense than the primary band and their formation can be attributed to the inclined nanofacets that form in the vicinity of the vertices.The formation of the secondary bands requires a higher composition of P in the shell,and to be grown under conditions that increase the diffusivity difference between As and P.Furthermore,it is observed that the primary band can split into two narrow and parallel bands.This can take place in all six radii,making the cross sections to have up to a maximum of 18 radial segregation bands.With controlled growth,these features could be exploited to assemble multiple different quantum structures in a new dimension(circumferential direction)within nanowires.

In situ Study on the Growth Behavior of Primary Al_3Ni Phase in Solidifying Al–Ni Alloy by Synchrotron Radiography

The growth behavior of Al_3Ni intermetallic compounds（IMCs）during the directional solidification of Al-10 wt%Ni alloy was investigated by synchrotron radiography.Two main growth patterns of primary Al_3Ni phase,I-like and V-like,appeared during solidification,and I-like Al_3Ni phase grew faster than V-like phase,which can be explained by the minimum energy criterion.The growth of I-like phase can be divided into two stages and was mainly affected by undercooling and Ni concentration.We also found that V-like Al_3Ni phase can evolve into M-like phase during solidification.