TiCr1.2(V–Fe)0.6—a novel hydrogen storage alloy with high capacity

To develop a new alloy with high hydrogen storage capacity, partial Cr in TiCr_1.8 was substituted by V—Fe alloy. X-ray diffraction and metallography observation proved that the substitution did not change the phase constitution of TiCr_1.2(V–F)_0.6. It still remained in its initial Laves phase related body centred cubic structure. Pressure–composition—temperature tests showed that the hydrogen storage capacity could reach up to 3.2 wt% and its reversible capacity to about 2.0 wt%. TG-DSC tests showed that there are two kinds of tetrahedral site for hydrogen atoms to locate.     

Comparison of hydrogen storage characteristics between as-cast and melt-spun TiCr1.1V0.5Fe0.1Mn0.1 alloys

Hydrogen storage characteristics of as-cast and melt-spun TiCr_1.1V_0.5Fe_0.1Mn_0.1 alloys were investigated by pressure–composition–temperature (PCT) tests, X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD showed that both the as-cast and the melt-spun alloys were similarly consisted of V based BCC phase and Ti_1.07Cr_1.93 phase. However, PCT tests showed that the melt-spun alloy, with larger hysteresis between hydrogen absorption and desorption, had higher hydrogen storage capacity than the as-cast alloy. More interestingly, the phase compositions of the two fully hydrogenated alloys were entirely different. The as-cast and the melt-spun alloys should have different atomic motion mechanisms during the course of hydrogenation.     

Solidification microstructures and mechanical properties of high-vanadium Fe–C–V and Fe–C–V–Si alloys

Fe–C–V and Fe–C–V–Si alloys of various C, V and Si compositions were investigated in this work. It was found that the phases present in both of these alloy systems were alloyed ferrite, alloyed cementite, and VC_x carbides. Depending on the alloy composition the solidified microstructural constituents were granular pearlite-like, lamellar pearlite, or mixtures of alloyed ferrite + granular pearlite-like or granular pearlite-like + lamellar pearlite. In addition, it is shown that in Fe–C–V alloys the C/V ratio influences (a) the type of matrix, (b) the fraction of vanadium carbides, f_v and (c) the eutectic cell count, N_F. In Fe–C–V alloys, a relationship between the alloy content corresponding to the eutectic line was experimentally determined and can be described by where C_e and V_e are the carbon and vanadium composition of the eutectic. Moreover, in the Fe–C–V alloys (depending on the alloy chemistry), the primary VC_x carbides crystallize with non-faceted or non-faceted/faceted interfaces, while the eutectic morphology is non-faceted/non-faceted with regular fiber-like structures, or it possesses a dual morphology (non-faceted/non-faceted with regular fiber-like structures + non-faceted/faceted with complex regular structures). In the Fe–C–V–Si system, the primary VC_x carbides solidify with a non-faceted/faceted interface, while the eutectic is non-faceted/faceted with complex regular structures. In particular, spiral eutectic growth is observed when Si is present in the Fe–C–V alloys. In general, it is found that as the matrix constituent shifts from predominantly ferrite to lamellar pearlite, the hardness, yield and tensile strengths exhibit substantial increases at expenses of ductility. Moreover, Si additions lead to alloy strengthening by solid solution hardening of the ferrite phase and/or through a reduction in the eutectic fiber spacings with a decrease in the alloy ductility.     

Compressive creep behavior of as-cast and aging-treated Mg–5 wt% Sn alloys

The microstructure and compressive creep behaviors of as-cast and aging-treated Mg–5 wt% Sn alloys are investigated in this paper. The compressive creep resistance of aging-treated Mg–5 wt% Sn alloy is much better than that of as-cast alloy at the applied stresses from 25 MPa to 35 MPa and the temperatures from 423 K to 473 K, which is mainly due to the dispersive distribution of Mg₂Sn phase in the aging-treated Mg–5 wt% Sn alloy. The calculated average values of stress exponent n and activation energy Q_c suggest that dislocation cross slip and dislocation climb happen respectively in as-cast and aging-treated Mg–5 wt% Sn alloys during creep.     

Electrochemical codeposition of magnesium and nickel alloy for hydrogen storage

Magnesium and nickel alloy was prepared electrochemically in dimethylsulfoxide (DMSO) solution. Its structure, composition and property for hydrogen storage were studied by SEM, ICP, XRD, and charge and discharge test. It is found that codeposition of magnesium and nickel can take place at the potentials from −2.0 to −3.2 V (vs. Ag/Ag⁺) in 0.15 M LiClO₄ + DMSO solution containing MgCl₂ and NiCl₂. The surface morphology and the hydrogen storage capacity of the prepared alloy are influenced by the deposition potential. The alloy prepared at −2.4 V (vs. Ag/Ag⁺) is mainly composed of Mg₂Ni phase and shows its best electrochemical capacity of 361.8 mAh g⁻¹, corresponding to a hydrogen storage capacity of 1.35 wt.%.     

Microstructure and Mechanical Properties of Rapidly Solidified Hypereutectic Al–Si and Al–Si–Fe Alloys

The microstructure and mechanical properties of rapidly solidified Al–18 wt% Si and Al–18 wt% Si–5 wt% Fe alloys were investigated by a combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile testing, and wear testing. The centrifugally atomized binary alloy powder consisted of the -Al (slightly supersaturated with Si) and Si phases and the ternary alloy powder consisted of the -Al (slightly supersaturated with Si), silicon, and needle-like metastable Al–Fe–Si intermetallic phases. During extrusion the metastable -Al₄FeSi₂ phase in the as-solidified ternary alloy transformed to the equilibrium -Al₅FeSi phase. The tensile strength of both the binary and the ternary alloys decreased with a high-temperature exposure, but a significant fraction of the strength was retained up to 573 K. The specific wear gradually increased with increasing sliding speed but decreased with the addition of 5 wt% Fe to the Al–18 wt% Si alloy. The wear resistance improved with annealing due to coarsening of the silicon particles.     

Interfacial microstructure of Si3N4/Si3N4 brazing joint with Cu–Zn–Ti filler alloy

In this study, Si₃N₄ ceramic was jointed by a brazing technique with a Cu–Zn–Ti filler alloy. The interfacial microstructure between Si₃N₄ ceramic and filler alloy in the Si₃N₄/Si₃N₄ joint was observed and analyzed by using electron-probe microanalysis, X-ray diffraction and transmission electron microscopy. The results indicate that there are two reaction layers at the ceramic/filler interface in the joint, which was obtained by brazing at a temperature and holding time of 1223 K and 15 min, respectively. The layer nearby the Si₃N₄ ceramic is a TiN layer with an average grain size of 100 nm, and the layer nearby the filler alloy is a Ti₅Si₃N_x layer with an average grain size of 1–2 μm. Thickness of the TiN and Ti₅Si₃N_x layers is about 1 μm and 10 μm, respectively. The formation mechanism of the reaction layers was discussed. A model showing the microstructure from Si₃N₄ ceramic to filler alloy in the Si₃N₄/Si₃N₄ joint was provided as: Si₃N₄ ceramic/TiN reaction layer/Ti₅Si₃N_x reaction layer/Cu–Zn solution.     

Mechanical and anisotropic behaviors of Mg–Li–Zn alloy thin sheets

This study examined the mechanical property and formability of the cold-rolled Mg–Li–Zn alloy sheets with two different Li contents. Uniaxial tension and press-forming tests were carried out at room temperature. The tensile properties and formability parameters were correlated with the forming limit diagrams. The test results indicated that the Mg–Li–Zn alloy with a Li content of 6 wt% exhibited reasonable strength levels with moderate fracture elongation and that it did not show good stretchability and drawability at room temperature. The alloy with a Li content of 9 wt% presented excellent ductility even at room temperature and the strength levels were somewhat inferior. From the analysis, it was found that formability of the alloy with a higher Li content of 9 wt% was superior compared to that of the alloy with a Li content of 6wt%. Moreover, the fracture surfaces of the press-formed samples were considered and studied under a scanning electron microscope (SEM). The results showed that the partly ductile and partly brittle fracture pattern was observed in the tension–tension strain condition for both the alloys.     

Microstructure and texture of rolled and annealed β titanium alloy Ti–10V–4.5Fe–1.5Al

This work describes the evolution of texture during cold rolling and annealing of a hot rolled and solution treated sheet of a low cost β titanium alloy Ti–10V–4.5Fe–1.5Al. The alloy was cold rolled up to 60% reductions and then annealed in β phase field at different temperatures to study the re-crystallisation textures. The rolling and re-crystallisation textures obtained in this study are compared with those of other β titanium alloys and bcc metals and alloys such as tantalum and low carbon steel.     

Interface interaction in the B4C/(Fe–B–C) system

The wetting behavior in the B₄C/(Fe–C–B) system was investigated in order to clarify the role of Fe additions on the sinterability of B₄C. Iron and its alloys with C and B react with the boron carbide substrate and form a reaction zone consisting of a fine mixture of FeB and graphite. The apparent contact angles are relatively low for the alloys with a moderate concentration of the boron and carbon and allow liquid phase sintering to occur in the B₄C–Fe mixtures. A dilatometric study of the sintering kinetics confirms that liquid phase sintering actually takes place and leads to improved mass transfer. A thermodynamic analysis of the ternary Fe–B–C system allows accounting for the experimental observations.     

Effect of precipitates on damping capacity and mechanical properties of Ti–6Al–4V alloy

The present study was concerned with the effects of over-aging on damping property and fracture toughness in Ti–6Al–4V alloy. Damping property and toughness become important factors for titanium implants, which have big modulus difference between bone and implant, and need high damping capacity for bone-implant compatability. Widmanstätten, equiaxed, and bimodal microstructures containing fine α₂ (Ti₃Al) particles were obtained by over-aging a Ti–6Al–4V alloy. Over-aging heat treatment was conducted for 200 h at 545 °C. Fracture toughness, Charpy impact, and bending vibration tests were conducted on the unaged and the over-aged six microstructures, respectively. Charpy absorption energy and apparent fracture toughness decreased as over-aging was done, even if the materials were strengthened by precipitation of very fine and strong α₂-Ti₃Al particles. On the other hand, damping properties were enhanced by over-aging in Widmanstätten and equiaxed microstructures, but was weakened in bimodal microstructure due to the softening of tempered martensite and the decreasing of elastic difference between tempered martensite and α phase contained α₂ particles, etc. These data can provide effective information to future work about internal damping and fracture properties of Ti–6Al–4V alloy.     

Synthesis of a nanostructured MgH2-Ti alloy composite for hydrogen storage via combined vacuum arc remelting and mechanical alloying

To improve the hydrogen kinetics of magnesium hydride, TiCr_1.2Fe_0.6 alloy was prepared by vacuum arc remelting (VAR) and the alloy was co-milled with MgH₂ to process nanostructured MgH₂-5 at.% TiCr_1.2Fe_0.6 powder. The hydrogen desorption properties of the composite powder were studied and compared with pure magnesium hydride. X-ray diffraction (XRD) analysis showed that the composite powder prepared by VAR/mechanical alloying (MA) procedure consisted of β-MgH₂, γ-MgH₂, bcc Ti-Cr-Fe alloy, and small amount of MgO. The average size of particles and their grain structure after 4 h MA were determined by a laser particle size analyzer and XRD method and found to be 194 nm and 11 nm, respectively. The hydrogen desorption temperature of magnesium hydride decreased from 426 °C to 235 °C by the bcc Ti alloy and the utilized processing method, i.e. combined VAR/MA.     

Processing and properties of Al–Li–SiCp composites

Al–Li–SiC_p composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 μm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macro- and microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ^′ (Al₃Li) and S^′ (Al₂CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.     

The hydriding–dehydriding characteristics of La0.6Y0.4Ni4.8Mn0.2 and their influences in the surface strain on small-scale, thin-wall and vertical containers

The hydriding–dehydriding characteristics of La_0.6Y_0.4Ni_4.8Mn_0.2 are studied, and the surface strain on small-scale, thin-wall and vertical containers is analyzed. According to the tests on 20–58.7 vol% schemes, prominent strain appears in both the hoop and the longitudinal directions. The surface strain increases with cycle numbers and packing fractions, while declines from the bottom to the top. The strain increments are linear with cycle numbers, and the absorption strain increments grow with atomic ratios. The alloy separates into agglomerated and loosened states after cycling. The optimal alloy packing scheme and hydrogen charge amount for the directly filled containers are proposed.     

Fabrication and optical properties of NUV-emitting SiO2–SrB4O7:Eu glass–ceramic thin films

SiO₂–SrB₄O₇:Eu²⁺ glass–ceramic thin films were fabricated for possible application in near ultraviolet (NUV) emitting devices. Nano-sized SrB₄O₇:Eu²⁺ powders were prepared by a Pechini-type sol–gel method and a subsequent ball-milling treatment. The powders showed NUV emissions centered at 367 nm, upon irradiation with UV of shorter wavelengths, due to an allowed 4f⁶5d¹ → 4f⁷ electronic transition of Eu²⁺ ions. The glass–ceramic thin films were prepared by dip-coating of tetraethylorthosilicate (TEOS) solutions dispersed with the nano-sized SrB₄O₇:Eu²⁺ powders and a subsequent heat-treatment. It was found that the glass–ceramic thin films had relatively high thermal stability up to 800 °C in terms of the Eu²⁺ emissions. SiO₂ layers surrounding SrB₄O₇:Eu²⁺ appeared to be effective for the surface passivation of the phosphor particles.     

Hypervelocity impact damage to Ti–6Al–4V meshes reinforced Al–6Mg alloy matrix composites

An Al–6Mg alloy matrix composite reinforced with Ti–6Al–4V meshes was fabricated by pressure infiltration method; its damage behaviors impacted by hypervelocity aluminum projectiles were investigated. Results showed that the thin Ti_f/Al–6Mg composite target exhibits better protection efficiency and energy absorption ability than Al–6Mg alloy target. With projectile sizes increasing, bulge and spallation were observed on the back of the composite target. The Ti–6Al–4V meshes were tensed and deformed drastically in the spallation region, where micro-damages such as interfacial debonding and cracks were dominant. Shear localization was the primary failure characteristic for thin Al–6Mg alloy target. The adiabatic shear bands were observed near the crater of Al–6Mg alloy, not in Ti_f/Al–6Mg composite target. It was ascribed to the Ti–Al interfacial bonding strength and the high temperature strength for Ti–6Al–4V alloy.     

The influence of microstructure on dwell sensitive fatigue in Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy

The fatigue behaviour of titanium alloy Ti–6.5Al–3.5Mo–1.5Zr–0.3Si (TC11) was examined at 520°C to study the effects of microstructural variation on the dwell sensitivity. Three microstructures (equiaxed, tri-modal and basketweave) were used in this study. When a 3-min dwell time was imposed at the peak of each cycle a significant fatigue life reduction was observed for all microstructures tested. Among the three microstructures, equiaxed microstructure showed the strongest fatigue life reduction. The basketweave microstructure had a little higher dwell-time fatigue life than tri-modal microstructure at low maximum stress levels. In all cases, extensive quasi-cleavage facets and planar slips with track-like dislocations have been intimately linked with the dwell sensitive fatigue response. The amount of quasi-cleavage facets and planar slips decreased with a decrease of the α phase content. A rationalization for planar slip was proposed based on the mechanism of dislocations shearing α₂ particles. It is believed that α₂ particle formation and oxidization effects played an important role in dislocation planar slip.     

Thermomechanical processing of Ti–5Al–5Mo–5V–3Cr

The constitutive behaviour and microstructural evolution of the near-β alloy Ti–5Al–5Mo–5V–3Cr in the α + β condition has been characterised during isothermal subtransus forging at a range of temperatures and strain rates. The results indicate that Ti–5Al–5Mo–5V–3Cr has a shallower approach curve, and therefore, offers a more controllable microstructure than the near-β alloy Ti–10V–2Fe–3Al. Flow softening is small in magnitude in both alloys in the α + β condition. The steady state flow stresses obey a Norton–Hoff constitutive law with an activation energy of Q = 183 kJ mol⁻¹, which is similar to the activation energy for self-diffusion in the β phase, suggesting deformation is dominated by dynamic recovery in the β matrix. Good evidence is found for the existence of ω phase after both air cooling and water quenching from above the β transus. In addition, dissolution of the α phase is found to be slow at near-transus temperatures.     

Synthesis and magnetic properties of Ni–SiO2 nanocomposites

Nanocomposite Ni_(1 − x)/(SiO₂)_x soft magnetic materials were synthesized by a simple sol–gel combined hydrogen reduction method. The crystal structure of the particles was determined by X-ray diffraction (XRD). The shapes and sizes of the metal particles embedded in the SiO₂ matrix were determined by transmission electron microscopy (TEM), and magnetic properties were measured by the vibrating samples magnetometer (VSM). The obtained nanocomposite material is composed of nanoparticles coated with a thin SiO₂ layer, and with the content of the silicon increase, the thickness of the silica shells increase and the saturation magnetization decrease. The diameter of Ni particle in the sample is about 30–40 nm. The influence of the Ni content and preparation conditions on the microstructures and magnetic properties were discussed.     

Optical bistability for ZnO–Nb2O5–TeO2 glasses

We examined the optical nonlinear properties of ZnO–Nb₂O₅–TeO₂. The absorption and Raman spectra were measured, the third-order nonlinear susceptibility was determined by degenerated four wave mixing technique. The magnitude of χ⁽³⁾ is about 1.0 × 10⁻¹² esu, larger than that of silica glasses, and the optical bistability was observed in a Fabry–Perot cavity.