Showing papers in "Journal of Alloys and Compounds in 2009"

Microstructure and mechanical property of as-cast, -homogenized, and -deformed AlxCoCrFeNi (0 ≤ x ≤ 2) high-entropy alloys

Abstract: To have a further investigation of their physical properties such as electrical, magnetic, and thermal properties, the microstructure and mechanical property of Al x CoCrFeNi alloys have to have a detailed and systematic study. We present the effects of Al content on microstructure and mechanical property of as-cast, -homogenized, and -deformed Al x CoCrFeNi alloys in this study. It shows that single FCC and single BCC solutions, and duplex FCC–BCC are principal phases in these alloys. The x intervals for duplex FCC–BCC of different states of these alloys are investigated. The spinodal decomposition of less Al–Ni and more Al–Ni phases is the major reaction during homogenization of the alloys. The morphology of the less and more Al–Ni phases is also discussed. There is no stress-induced phase transformation during 50%-rolling deformation, and the main strengthening mechanism is work hardening. The hardening ability of FCC was about twice that of BCC in this alloy system.

Effects of rare-earth elements Gd and Y on the solid solution strengthening of Mg alloys

Abstract: A number of Mg–Gd, Mg–Y binary and Mg–Gd–Y ternary alloys are investigated in terms of solid solution strengthening efficiency in this work. It is found that both gadolinium and yttrium in solid solution give a cn concentration dependence of the yield strength, where c is the solute atom concentration and n = 1/2 or 2/3. This simplified analysis illustrates that we are able to satisfactorily predict the ternary solid solution strengthening in Mg–Gd–Y alloys. Gd and Y in solid solution are found to give a considerably higher strengthening effect than Al and Zn. It is suggested that, in addition to the classical size and/or modulus misfits model, the valency effect may account for the enhanced strengthening of Gd and Y in Mg.

The relation between severe plastic deformation microstructure and corrosion behavior of AZ31 magnesium alloy

Abstract: The quest for ever, higher performance in structural applications has resulted in the outgoing development of new or improved materials with novel crystallographic textures, microstructures, and compositions. However, commercial applicability of such materials depends heavily on the development of economical and robust manufacturing methods. Due to the promise of excellent properties, such as superplasticity, high strength, good ductility, enhanced high cycle fatigue life, and good corrosion resistance, interest has grown in nanostructure bulk materials. Those materials are defined most often as materials exhibiting nanocrystalline grain structures and particle sizes below 100 nm in at least one dimension. In recent years, bulk nanostructure materials processed by methods of severe plastic deformation (SPD) such as equal channel angular extrusion (ECAE) have attracted the growing interest of specialists in materials science. The main object of this research is to compare the microstructural changing and corrosion behavior of magnesium alloy AZ31 after extrusion and severe plastic deformation by ECAE process. The ECAE process can produce intense and uniform deformation by simple shear and provides a convenient procedure for introducing an ultra fine grain size into a material. The samples were prepared by using hot extrusion methods. Hardness and AC and DC polarization tests were carried out on the extruded rods, and the microstructure was examined using optical, electron microscopy (SEM, TEM) and EDS. The results showed that the severe plastic deformation process affected both the microstructure and the corrosion behavior of AZ31 Mg alloy. These results can be explained by the effects of the process on microstructure of AZ31 Mg alloy such as grain size and dislocation density caused by the change in recrystallization behavior.

Microstructure and tensile behaviors of FCC Al0.3CoCrFeNi high entropy alloy

Abstract: Homogeneously spherical nanoprecipitates with a L12 ordered structure are observed in as-cast FCC Al0.3CoCrFeNi high entropy alloy, while their morphology changes to platelets after aging at 700 °C. The appearance of a yield drop and low work-hardening during tension reveals that these nanoprecipitates are coherent and have the characteristics of the Guinier–Preston zone. The 900 °C aged alloy displays micro-sized rod-shaped precipitates rich in Ni and Al instead of nanoprecipitates. There is no yield drop but high work-hardening occurs during tension. This rod-shaped phase has a B2 ordered structure and has the Kurdjumov–Sachs relationship with the FCC matrix.

Effect of alloying elements on microstructure and properties of multiprincipal elements high-entropy alloys

Abstract: Ten high-entropy alloys are prepared by an arc furnace. The microstructure and the properties of the alloys are investigated. FeNiCrCuCo and FeNiCrCuMo alloys consist of a single FCC solid solution. When Cu or Co in the alloys is substituted by Al, the microstructures of the alloys change to that of BCC solid solution or that of a BCC + FCC solid solution. The results show that Cu with a FCC structure promotes the formation of a FCC solid solution. Although Al has a FCC structure, it does not help the formation of a FCC solid solution. In addition, when Zr is added into the alloys, complicated compounds are present due to the stronger compound formation tendency between Zr and other components. It is found that the hardness of alloys with a BCC structure is higher than that of the alloys with a FCC structure. The hardness of the alloys increases with increasing of Al content. When complicated compounds are formed, the hardness increases further. The highest hardness reaches 566 HV due to the strengthening of the second phase precipitation.

Concepts for the design of advanced nanoscale PVD multilayer protective thin films

Abstract: Technological challenges in future surface engineering applications demand continuously new material solutions offering superior properties and performance. Concepts for the design of such advanced multifunctional materials can be systematically evolved and verified by means of physical vapour deposition. The classical multilayer coating concept today is well established and widely used for the design of protective thin films for wear and tribological applications. It has proven great potential for the development of novel thin film materials with tailored properties. In the past decade, the emerging new class of nanoscale coatings has offered to the material scientists an even more powerful toolbox for the engineering thin film design through a combination of the multilayer concept with new nano-coatings. Some examples are the use and integration of low friction carbon-based nanocomposites in advanced multilayer structures or the stabilization of a specific coating in another structure in a nanolaminated multilayer composite. This paper reviews the latest developments in hard, wear-resistant thin films based on the multilayer coating concept. It describes the integration of nanocrystalline, amorphous and nanocrystalline/amorphous composite materials in multilayers and covers various phenomena such as the superlattice effect, stabilization of materials in another, foreign structure, and effects related to coherent and epitaxial growth. Innovative concepts for future, smart multilayer designs based on an extremely fine structural ordering at the nanoscale are presented as well.

The Al–B–Nb–Ti system: IV. Experimental study and thermodynamic re-evaluation of the binary Al–Nb and ternary Al–Nb–Ti systems

Abstract: The thermodynamic description of the entire ternary Al–Nb–Ti system is obtained by CALPHAD modelling of the Gibbs energy of all individual phases, taking into account experimental data on phase equilibria and thermodynamic properties published and complemented by own experiments. The description includes a re-evaluation of the constituent binary Al–Nb system. Selected equilibrium calculations were performed with the Thermo-Calc software using the proposed description. They are shown to well reproduce experimental data on both, phase equilibria and thermodynamic properties in the entire Al–Nb–Ti system.

Nanoparticles Ni and NiO: Synthesis, characterization and magnetic properties

Abstract: The present investigation reports, the novel synthesis of nanoparticles Ni and NiO using thermal decomposition and their physicochemical characterization. The nanoparticles Ni powder have been prepared using [bis(2-hydroxyacetophenato)nickel(II)] as precursor. Transmission electron microscopy (TEM) analysis was demonstrated nanoparticles Ni with an average diameter of about 14–22 nm. The products were characterized by X-ray diffraction (XRD), TEM, high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared (FT-IR) spectroscopy. The magnetic property of Ni and NiO was studied with vibrating sample magnetometer (VSM).

Deformation and annealing behaviors of high-entropy alloy Al0.5CoCrCuFeNi

Abstract: This investigation explores the deformation and annealing behaviors of high-entropy alloys using a ductile high-entropy alloy of Al0.5CoCrCuFeNi. This alloy had excellent workability and exhibited a large work hardening capacity in both hot forging and cold rolling. The main deformation and hardening mechanisms during cold work are uniquely associated with the nanotwinning deformation of this alloy. The easy formation of nanotwins appears to result from the blockage by the Widmanstatten Cu-rich precipitates of local slip deformation in a space of several tens nanometers, and the low stacking fault energy, which promotes the nucleation of nanotwins. This alloy was fully annealed in 5 h at 900 °C, revealing its significantly higher resistances to static anneal softening than traditional alloys with comparable melting points. This resistance is attributable to extensive solution hardening, low stacking fault energy, and the effect of sluggish diffusion on high-entropy alloys.

Oxidation of Ti-6Al-4V alloy

Abstract: Air oxidation behaviour of a Ti–6Al–4V alloy was examined over the temperature range of 600–800 °C for different time intervals ranging between 0.5 and 72 h. In addition to the determination of the oxidation kinetics by weight gain measurements, oxygen diffusion zone (ODZ) depth and hardness measurements were conducted on the cross-sections of the oxidised alloys to investigate the diffusion kinetics of oxygen into the substrate. The rate of oxidation evaluated according to the weight gain measurements fitted parabolic kinetics between 600 and 700 °C and linear kinetics above 700 °C by yielding activation energies of 276 and 191 kJ/mol, respectively. Analysis of the ODZ depth and hardness measurements resulted in an activation energy of 202 kJ/mol for oxygen diffusion in Ti–6Al–4V alloy. Finally, the kinetics of oxidation and oxygen diffusion were evaluated by the analysis of the experimental data with respect to temperature-compensated time parameter.

Effect of cobalt substitution on structural, magnetic and electric properties of nickel ferrite

Abstract: A series of cobalt-doped nickel ferrite with composition of Ni (1− x ) Co x Fe 2 O 4 with x ranges from 0.0 to 0.8 (in steps of 0.2) was prepared by using standard ceramic technique. The confirmation of single-phase formation and structural analysis were carried out by employing X-ray diffraction technique. The electrical DC resistivity measurement was done by using usual two probe method in the temperature range from room temperature to 600 °C. Room temperature resistivity measurements show the decrease in resistivity with increase of cobalt concentration. The studies on resistivity as a function of temperature shows that all the sample obeys the semiconducting behavior. B–H hysteresis measurement was carried out at room temperature under the field of 2.4 kOe and this measurement with the increase of Co 2+ concentration yields the monotonic increase of saturation magnetization ( M s ) and decrease in coercive field ( H c ) at higher Co 2+ concentration ( x > 0.4). Ferrites with such behavior are important for magnetic recording media. In view of this, we have studied the various properties of Co-doped Ni ferrite.

Synthesis of Fe3O4 nanoparticles at 100 °C and its magnetic characterization

Abstract: Superparamagnetic iron oxide nanoparticles were synthesized by a novel, simple and cost-effective gel-to-crystalline method by alkalizing ferrous chloride with ammonium hydroxide at 80-100 degrees ...

Cation distribution and magnetic properties of Zn doped NiFe2O4 nanoparticles synthesized by PEG-assisted hydrothermal route

Abstract: Nanosize ZnxNi1−xFe2O4 spinel composites with x = 0, 0.2, 0.4, 0.6, 0.8 and 1 were synthesized by using surfactant (polyethylene glycol (PEG)) assisted hydrothermal route and characterized by TEM, XRD and VSM techniques. The crystallite size was calculated from different characterization methods, and magnetic core size was found to be in the range of 9–20 nm from VSM. All particles showed superparamagnetic character at room temperature and Ms decreased with increasing concentration of Zn 2+

Discontinuous and continuous precipitation in magnesium–aluminium type alloys

Abstract: The microstructure investigations of the AZ91 alloy and binary Mg–9 wt.% Al alloy after different heat treatments were presented. Solution annealing at 693 K for 26 h (with water quenching), followed by ageing at 423, 473, 543 and 623 K was carried out. After ageing at 423 K only discontinuous precipitates were observed whereas at 623 K only continuous ones were revealed in the microstructure of both alloys. At intermediate ageing temperatures (473 and 543 K) both discontinuous and continuous precipitates occurred competitively. Additional analyses revealed that after cooling a solid solution from 693 K (without quenching) only discontinuous precipitates were formed. On the other hand, after heating a supersaturated solid solution from room temperature to 665 K both discontinuous and continuous precipitates were observed simultaneously. On the basis of the obtained results a model of precipitate types dependent on heat treatments for Mg–9 wt.% Al alloys was proposed.

Improvement of corrosion resistance of pure magnesium in Hanks’ solution by microarc oxidation with sol–gel TiO2 sealing

Abstract: A composite coating was prepared on degradable magnesium (Mg) implant for improving its corrosion resistance in Hanks’ solution (a simulated body fluid). The composite coating was fabricated using a two-step process: (i) a thick and porous oxide layer (with pore size of a few μm) was first formed by microarc oxidation (MAO) in a silicate/fluoride containing electrolyte, and (ii) a top TiO2 sealing layer was formed on the porous layer by sol–gel dip coating followed by hydrothermal treatment. SEM imaging and EDS mapping revealed an average overall thickness of about 12 μm. XRD analysis showed that the MAO layer was composed of magnesium oxide and fluoride and the TiO2 was present as an amorphous phase. Both electrochemical impedance spectroscopic (EIS) and anodic polarization measurements consistently recorded an increase in the initial corrosion resistance of about 30 times due to the composite coating. Immersion tests also showed that the corrosion behavior of the coated samples was more stable over time, and the degree of corroded damage was much reduced compared with bare Mg. The porous MAO layer provided anchorage sites for the subsequent TiO2 sol–gel coating, which sealed the pores and hence significantly enhanced the corrosion resistance while direct sol–gel coating on bare Mg was not successful. The present results indicate that the corrosion resistance of Mg implants could be significantly improved by a simple method using non-toxic materials. The increase in corrosion resistance implies the possibility of using less bulky fixation plates, thus enhancing the potential of using Mg as degradable implants.

First-principles calculations of mechanical properties of tic and tin

Abstract: First-principles calculations are performed to investigate the elastic properties and hardness of TiC and TiN. The calculated elastic constants for TiC agree closely with the experimental results. TiC is of nearly elastic isotropic characteristic according to its Zener's anisotropy parameter, A = 0.91, while the value for TiN, A = 0.8, shows its higher degree of elastic anisotropy relative to TiC. The ratios of bulk modulus (B) to shear modulus (G), 1.31 for TiC and 1.42 for TiN, indicate their brittle nature. The estimated hardness for TiC is consistent with the experimental values, whereas that for TiN is about 30% higher than the experimental ones. And the ultra high hardness for TiC and TiN may attribute to the interactions between Ti-3d and non-metal (C or N) 2p electrons according to the electronic structure analysis.

Structure and optical properties of nanocrystalline NiO thin film synthesized by sol–gel spin-coating method

Abstract: NiO thin film was prepared by sol-gel spin-coating method. This thin film annealed at T = 600 °C. The structure of NiO thin film was investigated by means of X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). The optical properties of the deposited film were characterized from the analysis of the experimentally recorded transmittance and reflectance data in the spectral wavelength range of 300-800 nm. The values of some important parameters of the studied films are determined, such as refractive index (n), extinction coefficient (k), optical absorption coefficient (α) and band energy gap (Eg). According to the analysis of dispersion curves, it has been found that the dispersion data obeyed the single oscillator of the Wemple-DiDomenico model, from which the dispersion parameters and high-frequency dielectric constant were determined. In such work, from the transmission spectra, the dielectric constant (e{open}∞), the third-order optical nonlinear susceptibility χ(3), volume energy loss function (VELF) and surface energy loss function (SELF) were determined.

A study of the microstructure and hardness of two titanium alloys: Commercially pure and Ti–6Al–4V

Abstract: In this paper, the microstructure and hardness of two titanium alloys was determined and the results are presented and briefly discussed. Samples of the alloy for microstructural examination were prepared from the as-provided stock using standard metallographic procedures and then examined in a low magnification light optical microscope. Both microhardness and macrohardness measurements were made across the polished surfaces of the two titanium materials. Both the microhardness and macrohardness of the Ti–6Al–4V alloy was noticeably higher than the commercially pure counterpart. The intrinsic influence of alloy composition and secondary processing, i.e., annealing, on microstructural development is presented and hardness of the two alloys is highlighted. The role of microstructure in governing the hardness of the two titanium materials is discussed.

Low-temperature synthesis of BiFeO3 nanopowders via a sol–gel method

Abstract: Bismuth ferrite (BiFeO 3 ) nanopowders were synthesized by a sol–gel method at the temperature as low as 450 °C. The obtained sol was transparent and homogenous when the mixture ionic concentration was properly controlled with the help of ethylene alcohol. The preparation process of crystalline BiFeO 3 could be divided into three stages: (i) the evaporation of organics and decomposition of nitrogen-containing organics below 200 °C; (ii) the collapse of Bi–Fe gel network in the temperature range of 200–300 °C and (iii) the formation of BiFeO 3 nanopowders by the solid-state reaction between Bi 2 CO 3 O 2 and Fe 2 O 3 .

Hydrothermal synthesis and characterization of self-assembled h-WO3 nanowires/nanorods using EDTA salts

Abstract: One-dimensional (1D) self-assembled single-crystalline hexagonal tungsten oxide (h-WO3) nanostructures were synthesized by a hydrothermal method at 180 °C using sodium tungstate, ethylenediaminetetraacetic (EDTA) salts of sodium or ammonium, and sodium sulfate. Controlled morphological modification of h-WO3 nanowire bundles was achieved and hierarchical urchin-like structures were produced by simply substituting the sodium ions with ammonium ions in the EDTA salt solution. Self-assembled h-WO3 nanowire bundles and nanorods that formed urchin-like structures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. 1D self-assembled h-WO3 nanowire bundles of ∼100 nm diameter and 1–2 μm length were comprised of several individual uniform nanowires of 4–6 nm diameter. These individual nanowires served as building blocks of the bundles. Raman, cyclic voltammetry (CV), and photoluminescence (PL) spectroscopy studies revealed their structure, electrochemical response, and luminescence properties. The synthesis of 1D self-assembled h-WO3 nanowire bundles and urchin-like structures was differentiated by means of Na+- and NH4+-based EDTA salt solutions.

Synthesis and structural characterization of Al–B4C nano-composite powders by mechanical alloying

Abstract: This paper consists of two parts. In the first part, attrition milling of commercially available (0.7 μm) boron carbide (B 4 C) particles was optimized to prepare B 4 C nano-particles. In the second part of the study, mechanical alloying was successfully employed to synthesize metal matrix composite powders with a nanocrystalline Al 6061 alloy as the matrix and B 4 C as the reinforcement. Different amounts of B 4 C particles (5 wt.% and 10 wt.%) having various sizes of 90 nm (produced in the first part of study), 0.7 μm and 1.2 μm were mixed with different sized (21 μm and 71 μm) Al 6061 powder particles and they were milled for different times. The results showed that the nano-sized B 4 C particles may be fabricated when they were milled for 110 h. The size of powder particles in the milled powder mixture was affected by the initial size and content of B 4 C particles and Al powders. The SEM and TEM micrographs demonstrated a uniform distribution of B 4 C particles in aluminum powders after 8 h milling of an Al + B 4 C powder mixture. XRD results confirmed that the crystal size of aluminum reached to 57 nm after 16 h milling of powder mixture and addition of B 4 C resulted in a finer grain size of Al in the Al + B 4 C mixture during the early stages of milling.

Microstructure and mechanical properties of ultra-fine grains (UFGs) aluminum strips produced by ARB process

Abstract: Accumulative roll-bonding (ARB) process is a severe plastic deformation process capable of developing grains below 1 μm in diameter and to improve mechanical properties. In this study, strips of a commercial pure aluminum were ARB-processed to eight cycles, and their microstructures and mechanical properties were investigated. XRD and TEM studies of the strips showed grain refinement, and the TEM micrograph of the alloy ARBed for eight cycles showed ultra-fine grains (UFGs) of high-angle grain boundaries ∼360 nm in size. The ambient tensile strength and microhardness of the ARB-processed samples increased with the number of ARB cycles. Whereas, the elongation dropped abruptly at the first cycles, above which it remained nearly constant. With increasing ARB process, the bending strength increased and sliding wear resistance decreased. SEM fractography of fractured surfaces after tensile tests revealed that failure mode in ARB-processed aluminum was shear ductile rupture with elongated small dimples.

Effects of Si additions on intermetallic compound layer of aluminum–steel TIG welding–brazing joint

Abstract: Dissimilar metals of 5A06 aluminum alloy and AISI 321 stainless steel were butt joined successfully by TIG welding–brazing with 1100 pure Al, 4043 AlSi5 and 4047 AlSi12 filler metals. Si additions in the filler metal have great effects in preventing the growth of the IMC layer, and minimizing its thickness. The joint interface with pure aluminum consists of the θ-FeAl 3 in aluminum side and η-Fe 2 Al 5 in steel side, while the interfaces with Al–Si filler metals are the τ 5 -Al 7.2 Fe 1.8 Si in aluminum side and θ-Fe(Al,Si) 3 in steel side. And with 5 wt.% of Si additions, the IMC layer has the optimum mechanical properties, and the tensile strength of the joint reaches 125.2 MPa. The growth mechanism of the IMC layers is controlled by the dissolution and diffusion of Fe atoms in the liquid. At the same time, Si atoms aggregate in the interface and participate the IMC layer's formation.

Microstructure and mechanical properties of aluminum alloy matrix composite reinforced with nano-particle MgO

Abstract: In this research, aluminum alloy (A356.1) matrix composites reinforced with 1.5, 2.5 and 5 vol% nano-particle MgO were fabricated via stir casting method. Fabrication was performed at various casting temperatures, viz. 800, 850 and 950 °C. Optimum amount of reinforcement and casting temperature were determined by evaluating the density, microstructure and mechanical properties of composites. The composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Hardness and compression tests were carried out in order to identify mechanical properties. The results reveal that the composites containing 1.5 vol% reinforcement particle fabricated at 850 °C have homogenous microstructure as well as improved mechanical properties.

Improvement of formability of Mg–Al–Zn alloy sheet at low temperatures using differential speed rolling

Abstract: The differential speed rolling (DSR) with a roll speed ratio of 1.167 was carried out on an AZ31B magnesium alloy in order to investigate its effects on the formability. Compared with the normal rolled sheet exhibiting approximately the same average grain size, the Erichsen values of the DSR processed sheet with an inclination of basal pole in the rolling direction significantly increased by about 1.5 and 1.9 times at room temperature and at 423 K, respectively. The deep-drawing temperature limit for a drawing ratio of 1.5 was also lowered from 443 K to 423 K. The improvement of the press formability at low temperatures can be attributed to the texture modifications, which led to a lower 0.2% proof stress, a larger uniform elongation, a smaller Lankford value and a larger strain hardening exponent.

Optoelectronic characteristics of UV photodetector based on ZnO nanowire thin films

Abstract: The ZnO thin films were prepared on the quartz substrate by the sol–gel method and the UV photodetector was constructed on the ZnO thin films, with a circular spiral structure in contact 30 nm IrO2 electrodes. The ZnO thin films were crystallized at various temperatures (600–700 ◦ C) for 1 h in a pure oxygen atmosphere, then were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the crystallized thin film structures. From photoluminescence (PL) and I–V measurements, the 650 ◦ C thin film not only possessed better crystallization but also had nanowire structures that revealed excellent potential as a UV photodetector.

Effect of trace La addition on the microstructures and mechanical properties of A356 (Al–7Si–0.35Mg) aluminum alloys

Abstract: A356 hypoeutectic alloy is a heat-treatable Al–Si–Mg system with a normal composition of Al–7 wt.% Si and about 0.35 wt.% Mg which has widespread applications in the aerospace and automotive industries. The purpose of this study is to determine the influence of different amounts of La on the microstructures and mechanical properties of A356 alloys. The microstructures of as-cast samples were examined by using optical microscopy (OM), scanning electron microscopy (SEM) and image analysis. The mechanical properties were investigated by tensile test, and the quality index (Q = UTS + 150 × log (elongation)) was used to evaluate the modification efficiency of different La contents. The findings indicated that the modification efficiency in microstructures and mechanical properties of A356 alloy with 1.0 wt.% La are similar to those modified by the commercial modifier, 0.01 wt.% Sr. Furthermore, the results of thermal analysis reveal that there is no direct relationship between eutectic growth temperature and silicon morphology/modification rating.

Crystal structure and luminescence properties of SrxCa1 − xAlSiN3:Eu2+ mixed nitride phosphors

Abstract: This study was performed to characterize the crystal structure and luminescence properties of Eu 2+ -doped Sr x Ca 1 − x AlSiN 3 (0.2 ≤ x ≤ 1) red phosphor. Structural refinement was carried out using the Rietveld method. The unit cell volumes were shown to expand linearly with increasing Sr content throughout the whole solid solution range. As an end member, SrAlSiN 3 :Eu 2+ phosphor was synthesized under a high pressure of 190 MPa and high temperature of 2173 K. The phosphor crystallizes with an isotypic structure of CaAlSiN 3 in the orthorhombic space group Cmc2 1 with lattice parameters of a = 9.8087(1) A, b = 5.75600(8) A, c = 5.16614(7) A, and unit cell volume = 291.674(7) A 3 . This unit cell volume was larger than that of CaAlSiN 3 :Eu 2+ by 4%. The phosphor showed intense orange–red emission by 5d → 4f transition of Eu 2+ at around 610 nm. Through the whole range of solid solution, Eu 2+ -doped Sr x Ca 1 − x AlSiN 3 red phosphors showed a broad excitation band ranging from UV to visible light, and temperature characteristics comparable to those of CaAlSiN 3 :Eu 2+ at the Eu concentration of 0.8 mol%.

On tension–compression yield asymmetry in an extruded Mg–3Al–1Zn alloy

Abstract: The tension–compression yield asymmetry of an extruded Mg–3Al–1Zn alloy was examined by changing load directions and grain sizes in room-temperature mechanical tests. A criterion for the activation of deformation modes was proposed to analyze the effect of load direction on twinning activity. When the load angle was 45°, the twin area fractions after tension and compression resembled each other, and the corresponding ratio between compression yield stress and tension yield stress equaled 1.02. As the load direction was parallel or perpendicular to the extrusion axis, the yield stress and twinning activity in tension differed obviously from those in compression, resulting in marked tension–compression yield asymmetry. Although grain-coarsening promotes twinning in tension along extrusion axis, it cannot reduce the yield asymmetry. Further, the contributions of twinning to strain during yield deformation were evaluated based on the quantitative statistic of twin area fraction.

Studies on electrochemical behaviour of zinc-doped LiFePO4 for lithium battery positive electrode

Abstract: The effects of zinc oxide doping on LiFePO 4 have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic measurements. The XRD patterns demonstrate that the samples have the phase of LiFePO 4 with an ordered olivine structure indexed to the orthorhombic Pmna space group. Also, XRD patterns show with the presence of LiZnPO 4 phase for zinc oxide doped samples. The EIS results showed that the conductivity is enhanced by zinc oxide doping. The 2.5% ZnO-doped LiFePO 4 demonstrated higher conductivity than the 1.5% ZnO and 5% ZnO-doped LiFePO 4 or the un-doped sample. The CV curves show that 2.5% ZnO-doped LiFePO 4 has higher electrochemical reactivity for lithium insertion and extraction than the un-doped material. The mean redox potential is E 1/2 = 3.45 V vs. Li + /Li. The first discharge curve of the 2.5% ZnO-doped LiFePO 4 shows a mainly flat voltage plateau over the 3.45–3.5 V range, indicating the lithium extraction and insertion reactions between LiFePO 4 and FePO 4 . A specific discharge capacity of about 177 mAh g −1 was achieved, with little decrease during cycling.