Current Issue http://www.jmst.org EN-US http://www.jmst.org/EN/current.shtml http://www.jmst.org 5 Tensile and fatigue properties of free-standing as-rolled Cu foils were investigated by means of uniaxial tensile and dynamic bending tests. A special testing system was established to evaluate fatigue behavior of a microscale material subjected to dynamic bending load. The experimental results show that the yield strength increases, but the fracture strain and fatigue resistance decrease with decreasing foil thickness. Deformation and fatigue damage behavior was characterized. The size effect on tensile and fatigue properties of the Cu foils are evaluated to get further understanding of the mechanical behavior of the micrometer-scale metallic materials.

]]> The tensile and fracture behavior of DZ68 directionally solidified Ni-base superalloy was studied in the temperature range of room temperature (RT) to 1000°C. The fracture mode was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show the tensile strength and yield strength of DZ68 alloy increase slightly with increasing temperature, so that at 760°C its reach maxima value: 1214 and 1019 MPa, respectively. When the experimental temperature is higher than 760°C, the tensile and yield strengths decrease evidently and the ductility increases remarkably. The fractograph of fracture surface for the tensile specimen at room temperature shows a dimple-ductile fracture mode. The fractograph from 760 to 850°C shows a slide fracture mode. The fractograph from 900 to 1000°C exhibits a creep rupture mode with uneven deformation.

]]> Tensile and isothermal fatigue tests were carried out on an as-rolled Mg-12Gd-3Y-0.5Zr alloy and its heat-treated counterpart at different temperatures. The experimental results show that the ultimate tensile strengths of two alloys decrease very slowly with increasing temperature up to 200°C. The ultimate tensile strength of heat-treated Mg-12Gd-3Y-0.5Zr is slight lower than that of as-rolled counterpart; however, the fatigue strength of heat-treated alloy is higher. The mechanism of fatigue failure was nvestigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It shows that cyclic slip combined with environmental effect may be the main crack initiation mechanism.

]]> Zr_1-x Ti_xNiSn_0:975Sb_0:025 (x=0, 0.15, 0.25, 0.5) half-Heusler thermoelectric materials have been prepared by levitation melt, melt spinning and hot pressing. X-ray diffraction analysis and scanning electron microscopy observation showed that nearly single phase half-Heusler compounds were obtained for the levitation-melted ingots. The effects of Ti substitution and grain refinement by melt spinning have been studied. It is found that both the Ti substitution on the Zr site and the grain refinement can reduce the lattice thermal conductivity and total thermal conductivity. The maximum figure of merit ZT value achieved is about 0.47, which is comparable with the previously reported value of ~0.5 for Zr_0:5Ti_0:5NiSn.

]]> Polycrystalline NaCo₂O_4-δ materials were prepared using the urea auto-combustion method. The reaction process and crystal growth were investigated through X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), and Fourier transform infrared spectrometry (FTIR). The results indicate that the formation temperature of NaCo₂O_4-δ is about 620°C, which is lower than that for solid-state reaction. XRD results show that the texturing along c-axis occurred as the powders calcined at 700°C were pressed into pellets with subsequently sintering, and the degree of such texturing increases  with increasing sintering temperature. Surface morphologies by scanning electron microscopy (SEM) also indicate that the texturing show dependence on sintering temperature. The grains on the surfaces of the pellets sintered at 750 and 850°C have some growth trend along a-b planes, while the grains on the surface of the pellet sintered at 950°C show an obvious growth trend toward c-axis.

]]> A nonlinear optical single crystal of potassium pentaborate tetrahydrate (KB₅O₈? 4H₂O) has been grown from aqueous solution by using unidirectional crystal growth method of Sankaranarayanan-Ramasamy (SR) with a due modification in the growth assembly. Potassium pentaborate crystal of 60 mm length and 10 mm diameter has been grown along (100) plane with a growth rate of 3 mm per day within a period of 20 days. The grown crystal was subjected to single crystal X-ray diffraction analysis to confirm that the crystal belongs to the orthorhombic system. Some fundamental data such as valance electron plasma energy, Penn gap, Fermi energy and electronic polarizability of the grown crystal were calculated. The presence of borate in the grown crystal was confirmed by Fourier transform infrared (FTIR) spectroscopy. The optical transmission property of the grown crystal was analyzed using ultra violet (UV) visible spectral analysis. Surface morphology of the growth plane was observed using scanning electron microscopy (SEM). The mechanical strength of the crystals was found out using Vickers microhardness test along the growth axis. Frequency dependent dielectric constant of the grown crystal was studied for various temperatures along (100) plane.

]]> Effects of intermediate annealing temperature and time after hot working on recrystallization temperature (Tr) of Al-Mg-Sc-Zr alloy subjected to further cold working were investigated. It was found that Tr of cold worked alloy dropped with the rise of intermediate annealing temperature or extension of annealing time, due to coarsening of Al₃(Sc, Zr) particles during intermediate annealing. After annealed at 550°C for 1 h or 475°C for 50 h, Tr is nearly same as that in a Sc, Zr free 5A06 alloy. Coarsening mechanism was also discussed. After hot rolling, residual dislocations promoted diffusion of Sc and Zr atoms at the elevated temperature of the intermediate annealing. Easier diffusion sped the growth of the Al₃(Sc, Zr) particles, resulting in a coherency loss and quantity reduction of the particles.

]]> The growth of LaBr₃:Ce³⁺ crystal by the vertical Bridgman process in a nonvacuum atmosphere was reported. According to the dehydration procedure of LaBr₃·7H₂O and CeBr₃·7H₂O investigated by differential thermal analysis/thermogravimetry (DTA/TG), anhydrous LaBr₃ and CeBr₃ were prepared by heating LaBr₃·7H₂O and CeBr₃·7H₂O at 240-260°C for 5-6 h in dried HBr atmosphere. Using the feed materials prepared from the anhydrous lanthanon bromides, a 0.5 mole fraction Ce³⁺ doped LaBr₃ crystal with size of Φ25 mm×50 mm had been grown by vertical Bridgman process successfully. By sealing the feed material in a platinum crucible, the crystal could be grown in a nonvacuum atmosphere as the oxidization and volatilization of the melt could be avoided. The crystal was grown with the optimum conditions such as a growth rate of 0.5-1.0 mm/h and a temperature gradient of around 30°C/cm across solid-liquid interface under a furnace temperature of 850-880°C. The crystal was characterized by DTA/TG, X-ray diffraction (XRD), optical transmission, photoluminescence and X-ray stimulated luminescence measurement. The Bridgman process was confirmed to be promising for growing transparent LaBr₃:Ce³⁺ crystal with high optical quality.

]]> The cavitation erosion corrosion behaviour of ZQMn12-8-3-2 manganese-nickel-aluminum bronze and ZHMn55-3-1 manganese-brass was investigated by mass loss, electrochemical measurements (polarization curves and electrochemical impedance spectroscopy) and the cavitation damaged surfaces were observed by scanning electron microscopy (SEM). The results showed that ZQMn12-8-3-2 had better cavitation erosion resistance than ZHMn55-3-1. After the cavitation erosion for 6 h, the cumulative mass loss of ZQMn12-8-3-2 was about 1/3 that of ZHMn55-3-1. The corrosion current density of ZQMn12-8-3-2 was less than that of ZHMn55-3-1 under both static and cavitaiton condition. The free-corrosion potentials of ZQMn12-8-3-2 and ZHMn55-3-1 were all shifted in positive direction under cavitation condition compared to static condition. In the total cu-mulative mass loss under cavitation condition, the pure erosion played a key role for the two tested materials (74% for ZHMn55-3-1 and 60% for ZQMn12-8-3-2), and the total synergism between corrosion and erosion of ZQMn12-8-3-2 (39%) was larger than that of ZHMn55-3-1 (23%). The high cavitation erosion resistance of ZQMn12-8-3-2 was mainly attributed to its lower stacking fault energy (SFE), the higher microhardness and work-hardening ability as well as the favorable propagation of cavitation cracks for ZQMn12-8-3-2, i.e., parallel to the surface rather than perpendicular to the surface for ZHMn55-3-1.

]]> Sintered (300°C) porous pellets of Fe₂O₃ were electrolyzed to Fe in molten CaCl₂ (800-900°C) under argon at 1.8-3.2 V for 2-20 h. The laboratory scale experiments show that it was a potentially direct green method to produce Fe powder. At lower electrolysis voltage (<2.2 V), higher current efficiency (>90%) and smaller energy consumption (~3.0 kWh/kg) can be obtained. When the electrolysis voltage was above 2.4 V, the deposition of metal Ca from the salt lowered the current efficiency and increased the energy consumption. The electrolysis voltage also had effects on the micrographs of the reduced powder. The cubic particles can be seen in the products at the voltage lower than 2.2 V; when the voltage was higher than 2.2 V, it was nodular. The reduction proceeds at the cathode in two steps, i.e., from Fe₂O₃ to FeO and then to Fe. The oxygen emits at the anode. The process is potentially free of carbon emission and produces two useful products at both cathode and anode, promising a zero-emission technology for the extractive metallurgical industry.

]]> A series of alkali halide doped chalcohalide glasses (100-x)(0.9GeS₂-0.1Sb₂S₃)-xCsCl (x=5, 10, 15 and 20 mole fraction) were prepared. The absorption spectra and Raman scatting spectra of these glasses were measured. The optical band gaps Eopt were obtained from ultraviolet absorption edges. Z-scan technique was utilized to investigate the third-order nonlinear optical properties of GeS₂-Sb₂S₃-CsCl glasses. The value of Eopt increases and the third-order optical nonlinearity decreases with increasing CsCl content. Decreasing lone-pair electron and broadening the band-gap will provide less transition paths for nonlinear process, which play a key role in ultrafast third-order nonlinear optical responses of these chalcohalide glasses.

]]> Lead-free piezoelectric ceramics (1-y)Bi_0:5(Na_1-xLi_x)_0:5TiO_3-yBaTiO₃ with x=0-0.125 and y=0.02-0.12 were fabricated by a solid-state reaction process, and their dielectric, piezoelectric and ferroelectric properties were investigated. The results show that the addition of Li⁺ significantly improves the sintering performance and piezoelectric properties of the ceramics. X-ray diffraction (XRD) patterns indicate that the ceramics possess pure perovskite structure. At room temperature, the ceramics provide high piezoelectric charge constant d₃₃ (up to 210 pC/N), high planar electromechanical coupling factor kp (34.5%), large remanent polarization Pr (up to 40°C/cm²), and low coercive field Ec (3.0 kV/mm), which indicates that (1¡y)Bi0:5(Na_1-xLi_x)_0:5TiO₃-yBaTiO₃ is a good lead-free piezoelectric ceramic.

]]> The effects of substitution of Al for Co on magnetic and magnetocaloric properties of MnCo_1-xAl_xGe (x=0.00, 0.03, 0.05, 0.08, 0.10, 0.13, 0.15, and 0.20) compounds have been investigated by X-ray diffraction (XRD) and magnetization measurements. XRD exhibits that MnCo_1-xAlxGe compounds crystallize in the orthorhombic TiNiSi-type structure for x≤0.03 and in the hexagonal Ni₂In-type crystal structure for x>0.03. Magnetic measurements show that the Curie temperature can be tuned between 286 and 347 K by changing the Co/Al ratio. The maximum magnetic entropy change determined from the isothermal magnetization measurement by Maxwell relation reaches 1.52 J/(kgK) for x=0.08 in a field change from 0 to 1.5 T around 310 K.

]]> Transparent conducting molybdenum-doped zinc oxide (MZO) films were successfully prepared by radio frequency (RF) magnetron sputtering method on glass substrates under different substrate temperatures. The nature of MZO film is polycrystalline with hexagonal structure and a preferred orientation along c-axis. With increasing substrate temperature from room temperature to 400°C, the crystallinity of the films is deteriorated and the resistivity increases sharply due to both the decrease of carrier concentration and Hall mobility. The lowest resistivity achieved is 9.2×10^-4 ­Ω· cm with a high Hall mobility of 30 cm²·V^-1·s^-1 for the film deposited at room temperature. The average transmittance in the visible range exceeds 85% for all the samples. The optical band gap decreases from 3.30 to 3.25 eV with substrate temperature from room temperature to 400°C.

]]> The microstructure and magnetic properties of Co/Cr bilayer films were examined before and after post-deposition annealing by using transmission electron microscopy (TEM), X-ray diffraction (XRD) technique and vibrating sample magnetometer (VSM). A model of grain boundary (GB) Cr-rich phase growth involving GB diffusion derived from the Cr underlayer was proposed to elucidate the kinetics of the paramagnetic Cr-rich phase growth along Co GBs within the Co layer. The correlation of the GB Cr-rich phase formation with the magnetic Co grain isolation and accordingly, improvement of magnetic properties was experimentally investigated and discussed in detail. Our analysis results are well consistent with previous micromagnetic simulations on the improvement of magnetic properties by the magnetic grain isolation. The results provide some insights into the processing-structure-property relationships of the Co/Cr bilayer films, and thus suggest that the magnetic grain isolation be feasible not only in longitudinal recording media, but also be effective in tuning the exchange coupling of magnetic grains in perpendicular recording media via the GB diffusion from underlayer and/or overlayer.

]]> [AlN/FePt]₁₀, [AlN/FePt]10/Ag and Ag/[AlN/FePt]₁₀ thin films were deposited by magnetron sputtering onto 7059 glass substrates, then were annealed at 550°C for 30 min. It is found that introducing non-magnetic Ag underlayer can improve the ordering and (001) preferred orientation of FePt grains. Furthermore, the (001) texture of FePt grains increases with increasing Ag underlayer thickness. However, with Ag top layer given, it can only be observed that the ordering of FePt grains was promoted.

]]> The high-temperature oxidation behaviors of the NiCrAlYSi/P-YSZ thermal barrier coatings (TBCs) produced by electron beam-physical vapor deposition (EB-PVD) on directionally solidified (DS) and single crystalline (SC) Ni-based superalloy substrates were investigated. The cross-sectional microstructure investigation, isothermal and cyclic oxidation tests were conducted for the comparison of oxidation behaviors of TBCs on different substrates. Although TBC on DS substrate has a relatively higher oxidation rate, it has a longer thermal cycling lifetime than that on SC substrate. The primary factor for TBC spallation is the mismatch of thermal expansion coefficient (TEC) of the bond coat and substrate. The morphological feature of thermally grown oxide (TGO) has a strong influence on the TBC performance. By optimizing the elemental interdiffusion between bond coat and substrate, a high quality TGO layer is formed on the DS substrate, and therefore the TBC oxidation behavior is improved.

]]> Infiltration-in situ reaction synthesis of Cf/TiAl₃ composite was investigated. The as-cast material was obtained by titanium particles, carbon fibers and pure aluminum. Titanium particles and carbon fibers were mixed and pressed to form a preform firstly, and then molten pure aluminum was pressed into the preform, subsequently, cooled rapidly. In situ reaction samples were obtained by heating the as-cast material from 600 to 1000°C for 1 h. The microstructural evolution of in situ reaction samples was analyzed by scanning electron microscopy and energy dispersive X-ray. In addition, the phase composition of products was inspected by X-ray diffraction. Experimental results showed that the dominant product of TiAl₃ and a small amount of Al₄C₃ were formed at low temperature. While TiAl₃ was not stable at high temperature, along with its decrease, TiC phase became favorable. In the final products, TiAl₃, TiC and Al₄C₃ were detected. Thus, the in situ reaction for Ti-Al-C system composite proceeded a formed-decomposed-precipitated mechanism.

]]> The characterization of reinforcement in 15% SiC particles reinforced Al matrix composites processed by powder metallurgy route was studied by statistical method. During the analysis, a new approach for the estimation of the characterization of reinforcement was presented. The mathematic software MATLAB was used to calculate the area and perimeter of reinforcement, in which the image processing technique was applied. Based on the calculation, the fractal dimension, shape factor, reinforcement size distribution and reinforcement distribution were investigated. The results show that the reinforcement shape is similar to rectangle; the reinforcement size distribution is broad with the range of 1-12 μm; the topography of reinforcement is smooth; and the reinforcement distribution is inhomogeneous. Furthermore, the cell model based on the statistical characterization was established and tested.

]]> The effects of boron on the solidification behaviors of Ti45AlxB alloys were studied by high temperature samples. These samples were melted at 1823 K, followed by cooling to the designated temperature, and then quickly water-quenched to preserve the solidification features. Optical microscopy and scanning electron microscopy analysis shows that the solidus temperature of Ti45Al was really reduced by 20 K when adding 0.8 at. pct B, and it was also observed that boride precipitated before the appearance of β phase. Besides, solidification structure confirmed that B addition does not obviously refine β phase. α grain refinement by certain amount of B in alloy probably clarifies the mechanism of B refining lamellar microstructure at room temperature.

]]> Direct diffusion bonding of an orthorhombic Ti₂AlNb base alloy to a TiAl base alloy, Ti-22Al-23Nb-2Ta and Ti-46.2Al-2Cr-2Nb-0.15B (at. pct), was carried out and the interface microstructure, formation of new phase at the interface and joint strength were characterized. At low temperature, a new phase with AlNb₂-structure, Al(Nb, Ti)₂, was formed in the interface region adjacent to the O base alloy. The α₂ was found to be the major reaction product and developed in the interface region adjacent to the TiAl alloy as well as in the region adjacent to the O base alloy accompanying the formation of Al(Nb, Ti)₂. The occurrence of Al(Nb, Ti)₂ has been attributed to the different diffusivity of Nb and Al, leading to a eutectoid-like reaction. At relatively high temperature, Al(Nb, Ti)₂ did not form due to enhanced diffusion of Nb but a B2-enriched zone formed on the O alloy side instead after long holding time. Only when an appropriate interface microstructure was achieved by optimizing the bonding parameters, could the shear strength of the joint reach 80% of that of the TiAl base alloy.

]]> Monolayered Co and trilayered Co/Cu/Co were electroplated on 485 μm-diameter Cu wires using the bath pH 2.5. These wires can be functioned as magnetic sensors owing to their magnetoimpedance (MI) effect. By measuring at four different frequencies (100, 250, 500, and 1000 kHz) and Co thicknesses (2.5, 5.0, 10.0, and 25.0μm), the MI ratio of electroplated Co on Cu wires tended to increase with increasing Co thickness and frequency of the driving current. The Co/Cu/Co on Cu wires exhibited even higher MI ratio. The magnetic layer also regulated the magnetic inductions and anisotropy regardless of the size of nonmagnetic core. Nevertheless, the diameter of the Cu core had a significant effect on the MI ratio. By comparing with the 47.7μm-diameter Ag cores electroplated by Co and Co/Cu/Co of the same thickness, the Cu cores with a larger diameter gave rise to a larger MI ratio because their lower electrical resistance enhanced the crossing effect. Substantial MI ratio was observed even in a low frequency regime because the skin effect occurred at a low frequency in the case of electroplated wires with large core diameters.

]]> Microscale laser shock processing (¹LSP), also known as laser shock processing in microscale, is a technique that uses microscale focused laser beam to induce high pressure plasma and generates plastic deformation and compressive residual stress in target materials, thus improves fatigue or stress corrosion cracking resistance of MEMS (Micro Electromechanical Systems) devices made of such a material. Many works have been reported about the research and experiment for μLSP. But the diameters of 50-200 μm were used at the first time for this field, which was useful for treating micro-device components with larger area and curved surface. The excimer laser was used firstly on μLSP for shorter wavelength than that of used in previous researches. The determination method of laser spot size at micro-level spatial resolution was presented. Under these conditions, plastic deformation, the stress analysis and microhardness with different pulse number, pulse energy and pulse spacing were investigated. Especially the residual stress distribution with depth treated by ¹LSP, was first investigated. Experiment results showed that the material performance was improved remarkably after μLSP.

]]> A consistent empirical embedded-atom potential that includes a long range force was developed for fcc (facecentered cubic) metals and alloys. The proposed potential for pure metals does not require modification of the initial function form when being applied to alloy systems. The potential parameters of this model were determined by fitting lattice constant, three elastic constants, cohesive energy, and vacancy formation energies of the pure metals and the heats of solution of the binary alloys via an optimization technique. Parameters for Ag, Al, Au, Cu, Ni, Pd and Pt were obtained. The obtained parameters were used to calculate the bulk modulus, divacancy formation energy, crystal stability, stacking fault energy, vacancy migration energy, and melting point for each pure metal and the heats of formation and lattice constants for binary alloys. The predicted values were in good agreement with experimental results.

]]> Functionally graded steels were produced via electroslag remelting process using the primary electrodes of plain carbon and austenitic stainless steels. Charpy impact energy of as-prepared specimens was measured in the form of crack divider. The obtained results show that the impact energy of the specimens depends on the type and the volume fraction of the present phases. Based on the rule of mixtures, a mathematical model, which correlates the impact energy of functionally graded steels to the impact energy of the individual layers through Vickers microhardness of the layers, was presented. A good compatibility between the experimental results and those obtained from the model was observed.

]]> The Zr₅₅Al₁₀Ni₅Cu₃₀ bulk metallic glass plate were successfully welded to crystalline aluminum plates by using a friction stir welding (FSW) method. The welded zone was examined. No defects, cracks or pores were observed and no other crystalline phases except for aluminum were found in the welded joint. The strength of the joint is higher than that of aluminum. The glassy phase in the stir zone keeps the amorphous state, showing a successful welding. The storage modulus softens over the glass transition. And the weldability was discussed according to this phenomena.

]]> In this paper, microstructure and mechanical properties of welding metals in 610 MPa high strength low alloy (HSLA) were studied after high-heat-input welding. Both the base material and the weld joint proved excellent strength and toughness by vibratory electrogas arc (VEGA) welding under 90 to 100 kJ/cm heat-input. The heat-affected zone (HAZ) was comprised of fine-grain zone (FGZ) and coarse-grain zone (CGZ), which characterizes fine granular structure and lathing-bainite substructure. It has found that large quantity of dispersed TiN and M23C6 precipitates restrain structure growing in HAZ and strengthen the weldment together with dislocations in the welded joint.

]]> On basis of the similitude principles, the conception of virtual simulative component and the auxiliary value of welding residual stress which is deduced by the welding conduction theory, the relation of the welding residual stress between the simulative component and the practical component is attained. In order to verify the correctness of the relation, the research work is done from the view of the welding experiment and the numerical simulation about the simulative component and the practical component. Moreover, for the welding experiment and the simulation, the proportionality coefficient of dimensions between the simulative component and practical component is 1:1.5. The results show that the distribution of welding residual stress of the simulative component is the same as that of the practical component. The ratio of welding residual stress attained by the experiment or the simulation method between the practical runner and the simulative component is compared with the ratio got from the similitude principles. Moreover, the error is less than 10%. This provides a new idea to predict the welding stress distribution of large practical structure by the contractible physical model, which owns important theory meaning and practical engineering significance for the welding experiment or the numerical simulation of large welding structures.

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