The study on interfacial bonding strength of Ag-Ni, Ag-Cu in cold pressure welding

The area of combination actually is a kind of interfacial phenomena that exist on the surface or thin film. The properties of interface have important effect on the whole welded joint, even decide directly the interfacial bonding strength.The bonding strength of metals in cold pressure welding such as Ag-Ni (they are hardly mutual soluble ) and Ag-Cu( they are limited soluble ) are discussed in this paper. The results of the tensile test suggest that two kinds of welded joints have enough strength to satisfy with the demand for being used. Moreover, thermodynamics, crystal logy, physics and metal electronic microscopic analysis etc are adopted to further calculate the bonding strength. The results of test and theoretical analyses prove that Ag-Ni, Ag-Cu, especially, for Ag-Ni can .form strong welded joint which is higher than that of the relative soft base metals in cold pressure welding.     

Elastic and Thermo-physical Properties of Stannite-type Cu2ZnSnS4 and Cu2ZnSnSe4 from First-principles Calculations

Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) with optimum band gaps about 1.5 eV are important absorbers for solar cells. The elastic constants and the thermo-physical properties of the stannite-type CZTS and CZTSe are calculated by using density-functional theory (DFT) and the quasi-harmonic Debye model. The bonding strength along the [100] and [010] directions is the same to that along the [001] direction and the shear elastic properties of the {001} plane are anisotropic for CZTS and CZTSe. Both compounds exhibit ductile behavior due to their high ratio of bulk modulus to shear modulus (K/G). The values of thermal capacity are close to 200 J/(mol·K) at above 300 K, and the thermal expansion coefficients decrease with increasing pressure at same temperature. The entropy is variable by power-exponent, and the internal energy is almost linear with increasing temperature for CZTS and CZTSe. The Gibbs energy of CZTS is lower than that of CZTSe under same temperature and pressure. The Debye temperatures are 297 and 232 K, and Grneisen parameters are 2.36 and 2.37 for CZTS and CZTSe at 300 K, respectively.     

Substrate Effect on Microstructure and Performance of LTHVOF Sprayed Copper Coatings

The performance of copper coatings fabricated on three substrates by LTHVOF spraying process was researched.XRD shows that substrate material has little effect on phase composition of coatings,and there is no oxide in the three coatings almost.These coatings are dense,and demonstrate little difference on the microstructure of the inner part of the coatings.However,microstructure of bonding area between coating and substrate shows big difference,copper coatings bonds compacter on soft substrate aluminum than hard substrate steel.Bonding strength of coatings sprayed on the soft substrate is higher than that on the hard substrate.Microstructure analysis of fracture surface shows that strong mechanical alloying phenomena when copper particles deposited on aluminum substrate.The average bonding strength of copper coatings on 1Cr18Ni9Ti,45#steel and LY12 is relatively 18.83,17.49 and 32.14 MPa.Substrates have strong effect on microstructure and bonding strength,but little on phase composition...     

First-principles study on effect of pressure and temperature on structural, elastic, thermodynamic, and electronic properties of Ni3Al alloy

The influence of temperature and pressure on the electronic, elastic, structural, and thermodynamic properties of Ni3Al alloy was investigated by performing a first-principles study. The calculated elastic constants, equilibrium lattice constants, and elastic modulus agree well with the recorded theoretical and experimental data. The calculated elastic constants indicate that C11 is more sensitive than C12 and C44 to pressure. The Young’s modulus, bulk modulus, and shear modulus increase with an increase in pressure. The ratio of bulk to shear modulus (B/G) and anisotropy factor A were also analyzed. The Debye temperature was obtained by calculating the elastic constants, and it changed with the change in the pressure. The thermal expansion coefficient, normalized volume, heat capacity, bulk modulus, and Debye temperature Θ were determined and analyzed by using the quasi-harmonic Debye model at pressures of 0–60 GPa and temperatures of 0–1600 K. Finally, the density of states and Mulliken population were investigated and the effect of pressure on these was analyzed.     

THE INTERFACE OF TERNARY-BORIDE-BASED HARD CLADDING MATERIAL

The interracial microstructure of ternary-boride-based hard cladding material (YF-2) has been studied using scanning electron microanalyser (SEM),X-ray diffraction (XRD) and energy disperse spectroscopy (EDS). Results show that there are chemical reactions and elements diffusion in the interfacial zone, which make the interface bonding well and bonding strength ideal at the interface.The results gotten by studying of crack produced by Vickers indentation technique in the interfacial zone show that it is difficult to produce crack in the interface, the crack length in the cladding layer is longer than that to the interface,the crack which propagate to the interface stops at the interface rather than propagates along the interface.This suggests negligible residual stresses have developed because of thermal expansion mismatch. The bonding strength of the interface is 550MPa, which has been gotten by cutting test. The result gotten by analyzing the fracture surface shows that the fracture occurs at the side of cladding layer, which confirms that the bonding strength at the interface is higher than that in the cladding layer.     

Microstructure and properties of liquid film solution-diffusion welding interface for ZCuBe2.5 Alloy

The microstructures and properties of liquid film solution-diffusion welding interface for ZCuBe2.5 alloy have been studied using Cu-base powder. It reveals that the welding joint has high tensile strength up to 278 MPa,rational distribution of hardness and better matches with base materials in properties. Weld metal consists of the u-niform and fine α-Cu equiaxed grain and intergranular Cu5.6 Sn phase. The weld is well combined with base materi-als. The transition solid solution combination interface with a thickness of 150 μm has been formed. In the process of stable welding, the thickness of interface appears to have an increase linearly with bonding time. In the cases of same bonding time, the thickness of interface increases with an increase of temperature gradient, which will become even more apparent with the increase of bonding time.     

Phase stability and structural distortion of NiO under high pressure

The phase stability and structural distortion of NiO under high pressure were investigated using first-principles calculations based on density-functional theory. Different forms of exchange-correlation functional including LDA, GGA and GGA＋U were used in the present calculations. All of the three methods predict NiO to be AFM II ordering with the cell slightly compressed along [111] direction and also indicate that there is no structural phase transition of NiO under pressure up to 140 GPa, which are in agreement with the experiment. However, both LDA and GGA incorrectly predict the structural distortion under pressure especially above 60 GPa. Only when strong correlations are included in form of GGA＋U, structural distortion under high pressure can qualitatively agree with the experiment. The related mechanism was also analyzed and discussed. These results suggest that the strong electronic correlations still play a very important role in the properties of NiO under high pressure.     

Research on rare earth and iron-rich diamond-enhanced tungsten carbide composite button

At the present time in china, the binder used in tungsten carbide composite button is mainly cobalt, which is very expensive. In order to solve the problems, a new type of rare earth and iron-rich diamond-enhanced tungsten carbide with high abrasive resistance and high toughness against impact, which realizes to substitute ferrum for cobalt, has been developed. The key problems in making the button are to improve the mechanical properties of matrix and increase the welding strength between the diamond and the matrix. All these problems have been solved effectively by low temperature activation hot-press sintering, doping rare earth lanthanum in matrix and high sintering pressure. The properties of the button have been determined under laboratory conditions. The test results show that its hardness is more than 90 HRA, its abrasive resistance is 39 times more than that of conventional cemented tungsten carbide, and its toughness against impact is more than 200 J. All these data show the button has very good mechanical properties.     

Effects of molybdenum on the microstructure and mechanical properties of Ti（C,N）-based cermets with low Ni

The effects of Mo on the microstructure and mechanical properties of Ti（C,N）-based cermets with low Ni have been studied systematically. Different contents of Mo （4-12 wt.%） were added into Tl（C,N）-based cermets. Specimens were fabricated by conventional powder metallurgy and vacuum sintered at temperatures of 1440, 1450, and 1460℃ individually. The microstructure and fracture morphology were investigated by scanning electron microscope, and the mechanical properties such as transverse strength and hardness were measured. The results show that the microstructure is uniform and the thickness of rim phase is moderate when the content of Mo is 8 wt.%; the mechanical properties of the specimens sintered at 1450℃ are better than those sintered at 1440 and 1460℃. The integrated properties of transverse strength and hardness are the best when the content of Mo is 8 wt.% and the sintering temperature is 1450℃.     

MOLECULAR DYNAMIC SIMULATIONS OF MOLTEN NaF

The structure and transport properties in molten NaF have been studied using the method ofmolecular dynamics simulation. The calculations are based on two models of interionic potentials,which are Fumi-Tosi potential (FT) and the Fumi-Tosi potential without Van derWaals attractive item (FT). The radial distribution function (RDF) and the Na~+ andF~- self-diffusion coefficients have been calculated. The calculated results are in good agreementwith the experimental ones. The calculation shows that the two models give nearly identicalradial distribution function and self-diffusion coefficient, but the results of FTpotentialare a little better than those of FT potential.     

First-principles study on structural stability of 3d transition metal alloying magnesium hydride

A first-principles plane-wave pseudopotential method based on the density functional theory was used to investigate the energy and electronic structure of magnesium hydride （MgH2） alloyed by 3d transition metal elements. Through calculations of the negative heat formation of magnesium hydride alloyed by X （X denotes 3d transition metal） element, it is found that when a little X （not including Sc） dissolves into magnesium hydride, the structural stability of alloying systems decreases, which indicates that the dehydrogenation properties of MgH2 can be improved. After comparing the densities of states（DOS） and the charge distribution of MgH2 with or without X alloying, it is found that the improvement for the dehydrogenation properties of MgH2 alloyed by X attributes to the fact that the weakened bonding between magnesium and hydrogen is caused by the stronger interactions between X （not including Cu） and hydrogen. The calculation results of the improvement for the dehydrogenation properties of MgH2-X （X=Ti, V, Mn, Fe, Co, Ni, Cu） systems are in agreement with the experimental results. Hence, the dehydrogenation properties of MgH2 are expected to be improved by addition of Cr, Zn alloying elements.     

First-Principle Calculations of the MgYA_4(A=Co and Ni)Phase with AuBe_5-Type Structure

First-principles calculations have been performed to study the structural,mechanical and magnetic properties of the MgYCo_4 and MgYNi_4 phases in AuBe_5-type structure.The obtained values of cohesive energy as well as formation energy prove that the MgYCo_4 and MgYNi_4 phases have a good combination of structural stability and alloying ability,which is also supported by electronic structure.It is found that the magnetic moment of the MgYCo_4 phase is 19.06 μ_B per unit cell mainly owed to the 3d state of Co atom,and the MgYNi_4 phase exhibits no magnetism.Both the trigonal shear constant C_(44) and the shear modulus G of the Mg YNi_4 phase are larger than those of the MgYCo_4 phase.Plasticity of alloys has been estimated by the C_(11)-C_(12) and Young's modulus E,and C_(12)-C_(44),shear to bulk modulus ratio G/B and Poisson's ratio v have been studied to predict the ductility of alloys.According to the calculated results,the MgYCo_4 phase has better plasticity as well as ductility,compared with the MgYNi_4 phase.     

Additive manufacturing technologies of porous metal implants

Biomedical metal materials with good corrosion resistance and mechanical properties are widely used in orthopedic surgery and dental implant materials,but they can easily cause stress shielding due to the significant difference in elastic modulus between the implant and human bones.The elastic modulus of porous metals is lower than that of dense metals.Therefore,it is possible to adjust the pore parameters to make the elastic modulus of porous metals match or be comparable with that of the bone tissue.At the same time,the open porous metals with pores connected to each other could provide the structural condition for bone ingrowth,which is helpful in strengthening the biological combination of bone tissue with the implants.Therefore,the preparation technologies of porous metal implants and related research have been drawing more and more attention due to the excellent features of porous metals.Selective laser melting（SLM）and electron beam melting technology（EBM）are important research fields of additive manufacturing.They have the advantages of directly forming arbitrarily complex shaped metal parts which are suitable for the preparation of porous metal implants with complex shape and fine structure.As new manufacturing technologies,the applications of SLM and EBM for porous metal implants have just begun.This paper aims to understand the technology status of SLM and EBM,the research progress of porous metal implants preparation by using SLM and EBM,and the biological compatibility of the materials,individual design and manufacturing requirements.The existing problems and future research directions for porous metal implants prepared by SLM and EBM methods are discussed in the last paragraph.     

Effect of annealing treatment on the structural, optical, and electrical properties of Al-doped ZnO thin films

Highly conductive and transparent Al-doped ZnO (AZO) thin films were prepared from a zinc target containing Al (1.5 wt.%) by direct current (DC) and radio frequency (RF) reactive magnetron sputtering. The structural, optical, and electrical properties of AZO films as-deposited and submitted to annealing treatment (at 300 and 400 ℃, respectively) were characterized using various techniques. The experimental results show that the properties of AZO thin films can be further improved by annealing treatment. The crystallinity of ZnO films improves after annealing treatment. The transmittances of the AZO thin films prepared by DC and RF reactive magnetron sputtering are up to 80% and 85% in the visible region, respectively. The electrical resistivity of AZO thin films prepared by DC reactive magnetron sputtering can be as low as tering have better structural and optical properties than that prepared by DC reactive magnetron sputtering.     

第一性原理研究Al-Y合金在压力作用下的晶胞结构、力学性质、热力学性质和电子结构

The influence of structural, elastic properties, thermodynamics and electronic properties Al-Y alloy were investigated by using first-principles. The equilibrium lattice constant, elastic constants, and elastic modulus as calculated here agree with results of previous studies. Calculated results of bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio v and Debye temperature all increase as pressure increase, but the opposite is true for heat capacity cp. In addition, the Debye temperature for the phases reduces gradually as follows: Al2Y > Al3Y> AlY. Additionally, the G/B ratio indicates that AlY and Al3Y are ductile materials, while Al2Y is a brittle material, and that the ductility of AlY and Al3Y can be improved with increased pressure, while the brittleness of Al2Y does not improve with increased pressure. Finally, the paper presents and discusses calculations of density of states and charge populations as they are affected by pressure.     

Effect of microstructural parameters on the properties of W-Ni-Fe alloys

The aim of this research was to examine the effect of microstructural parameters on the tensile properties of dif- ferent compositions of tungsten heavy alloys. The microstructural parameters (grain size, connectivity, contiguity, and solid volume fraction) were measured and were found to have a significant effect on the tensile properties of tungsten-based heavy alloys. The microstructural parameters of W-Ni-Fe alloys are sufficiently different to present a range of me- chanical properties. It is concluded that the mechanical properties of tungsten heavy alloys largely depend on the micro- structural parameters and their ductility is particularly harmed when grains are contiguous.     

Heat Treatment and Properties of Nitrogen Alloyed, Martensitic, Corrosion-resistant Steels

This paper gives a short introduction to the typical process route and material properties of these steels in comparison to standard martensitic corrosiun-resistant steels. The typical response of these steels to various heat treatment parameters is shown and explained using the three grades M333, N360 and M340 (all made by Boehler Edelstahl GmbH) as examples, and the physical metallurgy of these steels and its consequences for practical heat treatment is explained. The correlation between tempering parameters and their effect on the toughness and corrosion properties is explained in particular detail, showing that these new steels not only offer far better properly combinations under the usual heat treatment parameters than standard martensitic corrosion-resistant steels, but that they also open the door to extending heat treatment combinations and properties.     

Research on the diffusion bonding of superplastic magnesium alloy

The elevated temperature tensile experiments have been carried out on the magnesium alloy and results indicate that the magnesium alloy has excellent superplastic property.Gleebe-1500 testing machine was used in the diffusion bonding experiment on the superplastic magnesium alloy.Then,the shear stength of the joints under different conditions is obtained through shear testing and the optimum processing parameters for the diffusion bonding are achieved.By metallurgical microscope and scanning electron microscope (SEM),it is revealed that the micromechanism of diffusion bonding is the slide of grain boundaries caused by the growth of grains and atom diffusion of the superplastic magnesium alloy.     

First-principles theory on electronic structure and floatability of spodumene

The band structure, density of states, Mulliken populations, and frontier orbital of spodumene crystal were calculated using the first-principles method based on the density functional theory(DFT) and further analyzed in detail. The calculation results reveal that the O in spodumene is the most active and easily links with H+in the water, but the active Li is very low, so it is better to add activator to increase the concentrate grade and recovery rate of spodumene in the flotation process. Si–O bonds in spodumene crystal are mainly covalent, since the covalency of Al–O bonds is stronger than that of Li–O bonds,and minerals dissociate along the weakest Li–O bonds. In addition, the study of the frontier orbital indicates that both O and Si atoms have large contribution to the frontier orbital in the spodumene crystal. Oleate and dodecylamine are used as the collectors of spodumene. The results contribute to the understanding of crystal structures of spodumene, and can be used in guiding related practical applications.     

Microstructure and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel

Two post-weld heat-treatments ( PWHT) , 900℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900~C oil quenched and low temperature tempered ( PWHTB ) , are employed to treat the weldment. Then the effect of two post-weld heat-treatment processes on the microstructure, mechanical properties and fiacture toughness of electron beam welded joints of 30CrMnSiNt‘2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fiacture toughness of both weld and heat-affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fiacture toughness of two EBW joints have no evident differences.