Bonding Character and Formation Energy of Point Defects of He and Vacancy on （001） Surface of bcc Iron by First Principle Calculations

The structure and energy of He impurities and vacancy on (001) surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found: some of He atoms at surface atomic layers (SAL) relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.     

Valence electron structures and properties of Ni-based corrosion resistant alloy

The corrosion resistance and mechanical properties were tested and compared for the newly synthesized as-cast, as-solution Ni-Cr-Mo-Cu corrosion resistant alloys and 1Cr18Ni9Ti austenitic stainless steel. Their valence electron structural units were constructed, and the relative parameters were calculated by means of the Empirical Electron theory of Solids and Molecules （EET）. The results show that, during alloy elements Cr, Mo and Cu entering Ni-matrix, the bonding strength nA and bonding energy EA of the strongest bond of the alloy are greatly increased, causing the stronger solid solution strengthening effects （about 30% increase in σb）. Also, as reinforcement of the main bond network and the improvement of stability of the alloy system due to the solution of these alloying elements in γ-Ni, the ionization of metal atoms in corrosion solution and the flow of electrons from anode to cathode would all be impeded during electro-chemical corrosion processes, which leads to the excellent corrosion resistant ability of the present Ni-Cr-Mo-Cu alloy （about 2-3 orders of magnitude as high as 1Cr18Ni9Ti austenitic stainless steel） in several highly aggressive solutions.     

Microstructure and properties of deformation-processed Cu-Fe in-situ composites

The effects of intermediate annealings on the microstructure, the strength and the electrical resistivity of deformation-processed Cu-Fe in-situ composites were studied. The results show that intermediate annealings favour the formation of uniform tiny fibres from the iron dendrites but they have no obvious effect on the strength of the composite. The bigger the strain is, the higher the strength is. As the strain increases, the resistivity increases due to the increase of interface density. Intermediate annealings result in notable decreasing resistivity due to the precipitation of the iron atoms from the Cu matrix and decrease of solute scattering resistivity. The doping with Zr improves the strength of the composite slightly and the ultimate tensile strength（UTS） increases about 10%. The colligated performances of deformation-processed Cu-11.5 % Fe and Cu-11. 5% Fe-Zr composites at strain η=5.37 are 64.6% IACS/752 MPa and 61.4% IACS/824 MPa respectively.     

Theoretical analysis of β-LaNi5Hx（5≤x≤8）： structure and energetics

The calculations of total energy, band structure, and electronic density of states and Mulliken population analysis of β-LaNi5Hx（5≤x≤8） were performed by adopting the method of total energy based on the density functional theory. The augmented plane wave function was selected as the basis set in combination with ultra-soft pseudo-potential technology. The influence of the amount of H absorbed in alloys was discussed in terms of geometry, electronic structure and thermodynamic derived from calculated results. The results show that the amount of H absorbed and the preferred site occupation of the absorbed hydrogen atoms were controlled by the position of H- bands and the energy gap between H-bands and conduction bands. The β-phase hydrides of LaNi5 are most stable when hydrogen atom capacity coating in the range of 6 ～ 7.     

Crystallinity and crystallization mechanism of lithium X-ray diffractometry aluminosilicate glass by

The crystallinity of lithium aluminosilicate（LAS） glass after crystallization were studied at different temperatures by X-ray diffractometry and the crystallinity of the standard glass ceramic with known crystal and glass phases was examined. The crystallization mechanism of LAS glass was analyzed by the crystallinity, with a formula relating the crystallinity （X） and temperature （T）. The results show that the calculated crystaUinity of LAS glass by XRD increases with the erystaUization temperature, in the range of 40%-50%, which is close to the calculated ones of standard samples with spodumene quartz ratio of 40%-70%. The activation energy of LAS glass is different within different temperature ranges; nEe is 125.44 kJ/mol at 710-810 ℃ and nEe is 17.42 kJ/mol at 810-980 ℃, which indicates different crystallization mechanisms. It has been proved that the required energy for crystallization of glass in the lower temperature range includes the interracial energy between glass and crystalline phase and the free energy difference of atoms in structures of glass and crystal, and in the higher temperature ranges only the interfacial energy between glass and crystalline phase is considered.     

Electronic structure and physical properties of hcp Ti3Al type alloys

According to the basic information of sequences of Ti and Al characteristic atoms in hcp Ti-Al system, the compositional variations of the electronic structure, atomic potential energies, atomic volumes, lattice constants and cohesive energies of the ordered hcp Ti3Al type alloys were calculated by the framework of systematic science of alloys（SSA）. The electronic structure of the hcp Ti3Al compound consisted of ψ4h^Ti and ψ0h^Al atoms is 0.75[Ar] （3dn）^0.573（3dc）^2.1685（4sc）^0.972（4sf）^0.3093＋0.25[Ne]（3sc）^1.32（3pc）^1.19（3sf）^0.49. The factors of controlling lattice stability are electronic structure, atomic energies and atomic concentration. The ψ4h^Ti atoms play a determinative role in forming D019 structure with a=0.287 2 nm, c=0.456 4 nm, atomic cohesive energy e=4.810 8 eV/atom and heat of formation △H=-0.332 8 eV/atom. These calculated values are in good agreement with experimental values （a=0.287 5 nm, c=0.46 0 nm, △H=-0.27, -0.29 eV/atom）. The calculated cohesive energy of the hcp Ti3Al compound is slightly bigger than that of the fcc Ti3Al.This is a good sign that makes it feasible to stabilized L 12 structure of the hcp Ti3Al compound by ternary element, The new element should have more dc-electrons than Ti-metal and occupy at the Ti-lattice points.     

Numerical simulation and experimental validation on fabrication of nickel-based superalloy Kagome lattice sandwich structures

Nickel-based superalloy lattice sandwich structures present higher stiffness,higher strength and higher temperature resistance in comparison with other metals.In this study,the Kagome unit was adopted to design the lattice sandwich structure and ProCAST software was used to simulate the filling and solidification processes of the nickel-based superalloy.Grain morphology and sizes of the nickel-based superalloy lattice sandwich structures were simulated by using of cellular automaton coupled with finite element model(CAFE),and indirect additive manufacture combining with investment casting were carried out to fabricate the nickel-based superalloy lattice sandwich structures.The calculated grain morphology and sizes are in good agreement with the experimental results.The grains are mainly equiaxed with an average size of about 500µm.The simulated results also show that the superheat of melting and the mold preheated temperature have significant influence on the grain size of the Kagome lattice sandwich structures,lower superheat of melting and mold preheated temperatures are encouraged to obtain the fine grains while assuring the integrity of the Kagome lattice sandwich structures for industrial application.     

Lattice parameters of Ti–4Al–2V alloy with thermal oxidation

In this study, the effect of thermal oxidation on the lattice parameters of Ti–4Al–2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1–7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 °C results in a gradual increase in a-parameter, whereas it goes through a maximum at higher temperatures(600 and 700 °C). The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment condition. It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium.     

Carbon solubility in Cu-based composite prepared by mechanical alloying

The powder mixture of Cu and graphite was mechanically alloyed （MA） in an oscillating type ball mill. The milling time was varied in order to investigate its influence on the microstructural evolution of mechanically alloyed powders. The phase constituent, alloying characteristics, grain size and lattice distortion of these powders were determined by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The results show that the C is confirmed to dissolve in the Cu lattice, forming solid solution of carbon in copper the lattice parameter of copper increases with carbon concentration increasing, up to a saturation value of about 4%C（mass fraction）. Higher ball-mill energy is beneficial for twins and nanograin formation.     

Critical power of keyhole formation in CW Nd：YAG laser deep penetration welding

The energy model was founded to calculate the critical power of keyhole formation by using the limit principle in CW （ continuous wave ） Nd： YAG laser deep penetration welding process. The model was validated by experiments. The results show that ＇.there are two errors between the calculated critical power of keyhole formation and that of experiments ： one is that the calculated results is less than those of experiments, which is caused by not considering the energy loss by heat conduction in the model of keyhole formation. The other is that there is 0. 9 mm error between the axis of the calculated curve of critical power with location of laser focus and that of experimental curve, which is induced by the excursion of laser focus in laser deep penetration welding. At last, the two errors were revised according to the analyses of the errors.     

Adsorption of atomic S and C on Mg（0001） surface

First-principle calculations based on density functional theory were used to study the adsorption of atomic sulfur and carbon on the Mg（0001） surface in a wide range of coverages from 1/4 ML（monolayer） to 1 ML. It is found that the adsorption of atomic S and C on the high coordinate hollow site is more energetically favorable than that on other adsorption sites. S atom is favorable to be adsorbed at on-surface site and C atom is favorable to be adsorbed at subsurface site. The results suggest that when the coverage increases, the binding energy for S and C atoms will decrease and the interaction between adsorbed atoms tends to be stronger. It indicates that as coverage increases, S-Mg and C-Mg interaction weakens.     

Structural Features of（Ce,La or Sr）（Mn or Co）O_3 NanoPerovskites as a Catalyst for Carbon Monoxide Oxidation

The collection of different cations in the A and B sites of ABO3 was explored for the regularity of perovskites phase formability.Here,Sr2？,La3？,and Ce4？are selected as the cations of site A.The site B is considered to be Mn or Co cations.XRD analysis and Fourier transform infrared spectroscopy results confirm the formation of perovskite structure for catalysts in which La3？and Sr2？are considered as the cations of site A.Ceria is detected as the main crystalline phase when Ce4？is selected to be cation of site A.It is found that the octahedral factor（rB/rO） takes the same important role as the tolerance factor to form cubic perovskite.Average crystallite size of the products was calculated by data of the XRD and measured by the TEM analysis.Results of the XRD and TEM studies were supported by the study of the particles size distribution,which was carried out in a particle size analyzer.The perovskite samples were also used for stoichiometric oxidation of carbon monoxide with air.     

Effect of rare earth （RE） on diffusion of aluminum atoms in aluminizing

The RE-aluminized coating and pure aluminized coating on 20 carbons steel were prepared by hot dip aluminizing method at 740 ℃. After diffusion treatment at 850 ℃for 4 h, the distribution of aluminum and lanthanum elements in the coating was analyzed with energy disperse spectroscopy（EDS） and electron probe microanalyses（EPMA）, and the lattice parameter ofa-Fe in the matrix of the coating was measured precisely by X-ray diffractometer（XRD）. The results show that RE permeates into the aluminized coating, leads to lattice disturbance and increases the depth of the aluminized coating. On the basis of the results, the expression of the diffusion coefficient of Al atoms is derived from the diffusion flow, and the effect of the high vacancy concentration and high concentration gradient of vacancies on the diffusion of Al atoms was analyzed by establishing the kinetics model of the vacancy mechanism of diffusion. The results show that the high vacancy concentration and high concentration gradient of vacancies in the RE-aluminized processes are the main reason why the diffusion coefficient of Al atoms in RE-aluminizing is bigger than that in pure aluminizing.     

Influence of interstitial content on mechanical properties of new type of near a titanium alloy at cryogenic temperature

The influence of interstitial content on mechanical cryogenic temperature was studied. The results show that properties of a new type of near a titanium alloy （Ti-Zr-Mo-Nb-Sn） at interstitial content affects the mechanical properties of the alloy at cryogenic temperature. Interstitial element atoms solving into lattice causes the increasing of degree of distortion, which limits the sliding and twinning of dislocations. Reducing interstitial content is beneficial to generation of dislocation sliding and deformation twins. With interstitial element content reducing, the impact toughness and the elongation of the alloy decrease rapidly while the strength decreases weakly. To obtain good over-all properties at cryogenic temperature, the interstitial element content in this alloy must be controlled to extra low grade.     

Site Occupation of Nb in γ-TiAI:Beyond the Point Defect Gas Approximation

Microalloying is an effective approach to improve the mechanical properties of γ-TiAl intermetallic compound.Knowledge about the site occupancy of the ternary alloying element in the crystal lattice of γ-TiAl is highly demanded in order to understand the physics underlying the alloying effect.Previous first-principle methods-based thermodynamic models for the determination of the site occupancy were based on the point defect gas approximation with the interaction between the point defects neglected.In the present work,we include the point defect interaction energy in the thermodynamic model,which allows us to predict the site occupancy of the ternary alloying element in γ-TiAl beyond the point defect gas approximation.The model is applied to the γ-TiAl-Nb alloy.We show that,at low temperature,the site occupancy of Nb atoms depends on the composition of the alloy:Nb atoms occupy the A1 sublattice for the Ti-rich alloy but occupy Ti sublattice for the Al-rich alloy.The fraction of Nb atoms occupying A1 sublattice in the Ti-rich alloy decreases drastically,whereas the fraction of Nb atoms on the Ti sublattice in the Al-rich alloy decreases slightly with increasing temperature.At high temperature,Nb atoms occupy dominantly the Ti sublattice for both the Ti-rich and Al-rich alloys.The interaction between the point defects makes the Ti sublattice more favorable for the Nb atoms to occupy.     

Microwave permittivity of SiC-Al2O3 composite powder prepared by sol-gel and carbothermal reduction

SiC-Al2O3 composite powder was prepared by sol-gel and carbothermal reduction method. The powder synthesized was characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM） to confirm the phase formation, and the thermodynamic analysis was performed systematically. Moreover, the variation of its microwave permittivity with different atomic ratio of Al/Si was investigated in the frequency range of 8.2-12.4 GHz. The results show that, the powder obtained consists of spherical particles of 300-400 nm in diameter, which are composed of SiC and Al2O3 microcrystal with the grain size of approximately 45 nm. The results of XRD accord with those of the thermodynamic analysis. It is impossible for Al atoms to dissolve in the lattice of SiC during the carbothermal reduction process. Along with the increase of atomic ratio of Al/Si in the xerogel, the amount of Al2O3 in the powder synthesized increases, which reduces both ε＇, the real part of complex permittivity, and tg δ（ε＂/ε＇）, the dissipation factor, where ε＂ is the imaginary part of complex permittivity.     

Kinetic and thermodynamic studies of adsorption of gallium(Ⅲ) on nano-TiO_2

Nano-TiO2 was employed for the adsorption of gallium from aqueous solution in batch equilibrium experiments to investigate its adsorption properties. It was found that the adsorption efficiency of Ga(Ⅲ) was more than 96% at pH 3.0. The adsorption capacities and rates of Ga(Ⅲ) onto nano-TiO2 were evaluated as a function of solution concentration and temperature. The results were analyzed using the Langmuir adsorption isotherms. Adsorption isothermal data could be well interpreted by the Langmuir model. The mean energy of adsorption, 15.81 kJ·mol-1, was calculated from the D-R adsorption isotherm. The kinetic experimental data properly correlate with the pseudo-second-order kinetic model. The thermodynamic parameters for the process of adsorption have been estimated. The △ H Οand △ GΟvalues of gallium(Ⅲ) adsorption on nano-TiO2 showed an endothermic and spontaneous nature of adsorption.     

Different grain refinement mechanisms of minor zirconium and cerium in magnesium alloys

Zirconium and rare earth element cerium were added in magnesium and magnesium alloys to study their different grain refinement mechanisms. The results show that zirconium has an obvious refinement effect on the cast grain of magnesium and its alloys without the alloy element Al because the crystal structure of zirconium is the same as magnesium matrix, and the lattice parameters are close to magnesium. Zirconium can decrease the grain size of magnesium from 150 to 20 pm. The rare earth cerium also has a grain refinement effect on Mg and Mg-Al alloy. The cerium atoms tend to remain in the liquid rather than solidify with the solvent atoms magnesium at the solid-liquid interface. The liquid constitutional undercooling can provide a heterogeneous crystal nucleation. The grain is refined from 200 μm to 40-80 μm. These two elements have different grain refinement mechalfism on Mg alloy. The mechanism of zirconium is that it acts as the nuclei of α-Mg. But the mechanism of cerium is that it increases the liquid constitutional undercooling that can provide a heterogeneous crystal nucleation for the alloy.     

Influence of CaF2 on the structure and dielectric properties of Ag（Nb0.8Ta0.2）O3 ceramics

Ag(Nb0.8Ta0.2)O3 ceramics were prepared by the traditional solid-state reaction method. The effect of CaF2 addition on the structure and di-electric properties of Ag(Nb0.8Ta0.2)O3 ceramics was investigated. The addition of CaF2 led the ceramics to a larger grain size and distortion of lattice. With the addition of 4.5 wt.% CaF2, the permittivity of the ceramics increased from 442 to 1028, the dielectric loss decreased sharply from 6.12 × 10-3 to 8.6 × 10-4, and the temperature coefficient of capacitance decreased from 1834 ppm/°C to-50 ppm/°C (at 1 MHz). These results indicated that the high permittivity was related with a large grain size, a low grain boundary density, and the weak Ta-O or Nb-O bond strength caused by the addition of CaF2.     

Effect of minor Sc and Zr addition on microstructures and mechanical properties of Al-Zn-Mg-Cu alloys

Three kinds of Al-Zn-Mg-Cu based alloys with 0.22%, 0.36%（Sc＋Zr） （mass fraction, %）, and without Sc, Zr addition were prepared by ingot metallurgy. By using optical microscopy, transmission electronic microscopy and scanning electron microscopy, the effects of microalloying elements of Sc, Zr on the microstructure of super-high-strength Al-Zn-Mg-Cu alloys related to mechanical properties were investigated. The tensile properties and microstructures of the studied alloys under different heat treatment conditions were studied. The addition of minor Sc, Zr results in the formation of Ala（Sc,Zr） particles. These particles are highly effective in refining the microstructures, retarding recrystallization, pinning dislocations and subboundaries. The strength of Al-Zn-Mg-Cu alloys was greatly improved by simultaneously adding minor Sc, Zr, meanwhile the ductility of the studied alloys remains at a higher level. The 0.36%（Sc＋Zr） alloys gain the optimal properties after 465 ℃/h solution and 120 ℃/24 h aging. The increment of strength is mainly due to strengthening of fine grain and substructure and precipitation ofAl3（Sc, Zr） particles.