Rapid determination for fatigue parameters of AZ31B magnesium alloy based on evolution of temperature under high cyclic fatigue

Abstract

Based on the infrared thermography method, experiments are carried out to investigate the evolution of temperature field of the extruded AZ31B magnesium alloy specimens under high cyclic fatigue load. The experimental results show that the superficial temperature of specimen under cyclic fatigue load changes with the number of cycles. According to the characteristics of surface temperature change, we propose a formula to calculate the residual fatigue life using energy approach. The proposed formula to assess the fatigue parameters (fatigue limit, residual fatigue life, fatigue life and S–N curve) achieves good results for AZ31B magnesium alloy. Furthermore, the fatigue limits (Δσ_eSN?=?90·3 MPa) derived from the traditional method through 10⁷ cycles were compared with the values predicted by the infrared thermographic method (Δσ_eTM?=?87·3 MPa) and the energy approach (Δσ_eΦ?=?86·2 MPa), and the comparison results of percentage differences are 3·3 and 4·5% respectively.     

Preparation of nanocrystalline VMg(OH)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> and VO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> · MgO from organometallic precursors

A process is proposed for the synthesis of nanocrystalline VMg(OH) _x and VO _x · MgO with specific surface areas of up to 1200 and 470 m²/g, respectively. The synthesized VO _x · MgO oxides consist of nanocrystals (2′–5 nm), which form platelike agglomerates. As distinct from conventional impregnation of magnesium oxide, the aerogel process for VO _x · MgO synthesis ensures a uniform vanadium distribution in MgO.     

Magneto-dielectric effect in Pb(Zr0·52Ti0·48)O3 filled nanoporous Ni 0 ·5Zn 0 ·5Fe 2 O 4 composite

Nanoporous Ni_0·5Zn_0·5Fe₂O₄ particles of diameter, ~ 9·5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m² g^???1 and the average pore diameter was 2·5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr_0·52Ti_0·48)O₃ was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2·4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni_0·5Zn_0·5Fe₂O₄ which exerted a compressive strain on Pb(Zr_0·52Ti_0·48)O₃ thereby lowering the tetragonality in its crystal structure.     

Effect of Mg/nano-Al2O3 interaction time during stirring on microstructure and mechanical properties of Mg–Al2O3 composite

Abstract

In the present study, magnesium based composites containing 1·1 vol.% of alumina particulates at nanolength scale were synthesised using disintegrated melt deposition technique. The main focus was to vary interaction time between molten magnesium and nano-Al₂O₃ particulates during stirring and to study its effects on the microstructure and mechanical properties. With an increase in stirring time, microstructural characterisation of the composite materials revealed reasonably uniform distribution of Al₂O₃ reinforcement, marginal grain refinement and presence of minimal porosity. Mechanical properties characterisation revealed that an increase in stirring time led to a simultaneous increase in hardness, 0·2% yield strength and ultimate tensile strength while ductility was compromised beyond 7·5 min stirring when compared to pure Mg. The optimal stirring time is observed to be in 5–7·5 min range in order to realise the best combination of strength, hardness, ductility and work of fracture.     

Controlled synthesis and electrochemical properties of vanadium oxides with different nanostructures

Vanadium oxides (V₃O₇·H₂O and VO₂) with different morphologies have been selectively synthesized by a facile hydrothermal approach using glucose as the reducing and structure-directing reagent. The as-obtained V₃O₇·H₂O nanobelts have a length up to several tens of micrometers, width of about 60?C150?nm and thickness of about 5?C10?nm, while the as-prepared VO ₂ (B) nanobelts have a length of about 1·0?C2·7???m, width, 80?C140?nm and thickness, 2?C8?nm. It was found that the quantity of glucose, the reaction temperature and the reaction time had significant influence on the compositions and morphologies of final products. Vanadium oxides with different morphologies were easily synthesized by controlling the concentration of glucose. The formation mechanism was also briefly discussed, indicating that glucose played different roles in synthesizing various vanadium oxides. The phase transition from VO₂(B) to VO₂(M) were investigated and the phase transition temperature of the VO₂(M) appeared at around 68 °C. Furthermore, the electrochemical properties of V₃O₇·H₂O nanobelts, VO₂(B) nanobelts and VO₂(B) nanosheets were investigated and they exhibited a high initial discharge capacity of 296, 247 and 227 mAh/g, respectively.     

Hysteresis,structural and composition characteristics of deposited thin films by reactively sputtered titanium target in Ar/CH4/N2 gas mixture

Abstract

Hysteresis, crystal structure and chemical composition of thin films deposited through reactive sputtering of titanium metal target in Ar/CH₄/N₂ gas mixture have been investigated. The transition from metallic to compound sputtering mode was clearly seen as the reactive gases (CH₄ and N₂) flowrate concentration first increased and subsequently decreased. Abrupt cathode current drop from 273 mA to reach a minimum value of 195 mA was observed upon addition of nitrogen gas from 0 to 10% flowrate concentration to the Ar/CH₄ gas mixture. This was also accompanied by an abrupt change in reactive gas partial pressure. Exploration of the deposition rate and film thickness showed that it decreased from 4·5 to 1·5 nm min^?1 and from 140 to 40 nm as the N₂ flowrate concentration increased from 1·5 to 7·5% at 5·5%CH₄ flowrate concentration respectively. X-ray diffraction and X-ray photoelectron spectroscopy analyses of the deposited films confirmed the formation of titanium carbide and carbonitride phases as the methane and nitrogen gas concentrations in the sputtering gas were increased.     

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

MgTiO3/MgTi2O5/TiO2 heterogeneous belt-junctions with high photocatalytic hydrogen production activity

An effective photocatalytic hydrogen production catalyst comprising MgTiO₃/MgTi₂O₅/TiO₂ heterogeneous belt-junctions was prepared using magnesium ions by a thermally driven doping method. The tri-phase heterogeneous junction was confirmed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). The as-prepared MgTiO₃/MgTi₂O₅/TiO₂ heterojunctions exhibited a very high photocatalytic hydrogen production activity (356.1 mol·g_0.1gcat·h^-1) and an apparent quantum efficiency (50.69% at 365 nm) that is about twice of that of bare TiO² nanobelts (189.4 mol·g_0.1gcat·h^-1). Linear sweep voltage and transient photocurrent characterization as well as analysis of the electrochemical impedance spectra and Mott–Schottky plots revealed that the high photocatalytic performance is caused by the one-dimensional structure, which imparts excellent charge transportation characteristic, and the MgTiO₃/MgTi₂O₅/TiO₂ tri-phase heterojunction, which effectively drives the charge separation through the inherent electric field. This titanate-based tri-phase heterogeneous junction photocatalyst further enriches the catalyst system for photocatalytic hydrogen production.

     

Dense pure binderless WC bulk material prepared by spark plasma sintering

The phases, microstructures and mechanical properties of binderless WC bulk materials prepared by the spark plasma sintering technique were investigated systematically. The addition of carbon was added to eliminate the impurity phase W₂C. The relative density, Vickers hardness and grain size increase obviously with increasing sintering temperature, but increase weakly with increasing pressure or sintering time. The high relative density of 99·1%, HV30 of 27·5 GPa and fracture toughness K_IC of 4·5 MPa m^1/2 of pure binderless WC bulk with a grain size of 400 nm was obtained by sintering the WC powders with a particle size of 200 nm and the addition of 0·63 wt-%C at 1800°C for 6 min under 70 MPa.     

Synthesis of magnetite (Fe3O4) nanoparticles without surfactants at room temperature

Iron oxide nanoparticles in the interval of 4–43 nm were synthesized by a colloidal method at room temperature, without use of surfactants and using precursors like FeCl₃·6H₂O and FeCl₂·4H₂O; deionizated water free of dissolved oxygen and ammonia solution (29% vol.) and using several aging times (2, 5 and 10 min). A detailed study by X- ray diffraction (XRD), Conventional Transmission Electron Microscopy (CTEM), High-Resolution Transmission Electron Microscopy (HRTEM) and electron diffraction patterns showed that with a reaction time less than 5 min nanoparticles of magnetite phase (Fe₃O₄) were synthesized, and with a bigger time of reaction the lepidocrocite phase (FeO(OH)) was identified. The minor particle average size measured was 6 nm in the sample, 0.0125 M with 2 min of aging time (0.0125M2 m). In addition it was possible to obtain a narrow nanoparticle size dispersion from 4 to 10 nm for small aging times.     

Transformation of precipitated phases in Zr50·5Cu34·5−xNi4Al11Agx alloy master ingots with adding Ag

Abstract

The transformation of precipitated phases of Zr_50·5Cu_34·5?xNi₄Al₁₁Ag_x alloy master ingots with Ag substitution of Cu was studied in detail by phase analysis. The precipitated (Zr–Cu) rich phases deteriorate the glass forming ability (GFA) of Zr_50·5Cu_34·5Ni₄Al₁₁. Two new (Zr–Cu) rich phases, A1 with bcc structure and a?=?0·339 nm and A2 with fcc superlattice structure and a?=?1·21 nm, were identified by a transmission electron microscope. When x?=?2, A1 phase disappears, and A2 phase remains and is suppressed gradually with further Ag addition. When x?=?13, one precipitated phase with Ag more than 13 at-% begins to deteriorate GFA. In the view of chemistry, the precipitation of (Zr–Cu) rich phases means that the interaction between Cu and Zr atoms is rather drastic. The addition of Ag weakens the interaction between Cu and Zr. The similar competition mechanism proposed by the authors plays an important role in suppressing precipitated phases and improving GFAs.     

Development of ternary Mg based alloy for soldering of AZ31B magnesium alloy

Abstract

Two kinds of ternary Mg based alloys were designed to join the AZ31B magnesium alloy plates by high frequency induction soldering with argon shielding gas. The microstructures and properties of the filler metals and joints were investigated by SEM, X-ray diffraction, differential scanning calorimetry, spreading test and tensile test. The results have shown that the microstructures of Mg–31·5Al–10Sn filler metal mainly consist of Mg₁₇Al₁₂, Mg₂Sn and a trace amount of α-Mg phases, while the microstructures of Mg–29·5Zn–1Sn filler metal include α-Mg phase and Mg₇Zn₃ with a trace of α-Mg and Mg₂Sn phases. Both of the filler metals have narrow melting zones; however, the spreading area of the Mg–31·5Al–10Sn filler metal is much larger than that of the Mg–29·5Zn–1Sn filler metal on the AZ31B base metal. The average tensile strength of solder joints with Mg–31·5Al–10Sn filler metal is a little higher than that of the latter solder joints with Mg–29·5Zn–1Sn filler metal.     

Synthesis of hydrophobic aerogels for transparent window insulation applications

Abstract

The present paper deals with the synthesis of hydrophobic aerogels using methyltrimethoxysilane (MTMS) as a hydrophobic agent for transparent window insulation applications. The molar ratio of methanol (solvent), water, and ammonia (catalyst) to the tetramethoxysilane (precursor) MeOH/H₂O/NH₄OH/TMOS was fixed at 12/4&/3·6×10^-3/1 throughout the experiments and the MTMS/TMOS molar ratio M was varied from 0 to 1·55. After gelation, the alcogels were dried supercritically using the high temperature alcohol method. It has been found that lower (<0·26) M values resulted in highly transparent (optical transmission >90% for a 10 mm thick sample at 800 mm wavelength) and negligible volume shrinkage (<2%) but less hydrophobic aerogels whereas higher (>1·03) M values resulted in semitransparent (<20% optical transmission of 800 nm for a 1 cm thick sample) aerogels with >10% volume shrinkage but excellent hydrophobicity. A good compromise of acceptable optical transmittance (～85% optical transmission at 800 nm for a 1 cm thick sample), hydrophobicity with 42 kg m^-3 bulk density, and negligible volume shrinkage were obtained at M≈0·70. Hydrophobicity of the aerogels was tested by measuring the contact angle between a water droplet and the aerogel surface. The aerogels were characterised by infrared spectroscopy, bulk density, optical transmittance, and thermal conductivity measurements.     

Hydriding and dehydriding rates and hydrogen-storage capacity of Mg–14Ni–3Fe2O3–3Ti prepared by reactive mechanical grinding

The magnesium prepared by mechanical grinding under H₂ (reactive mechanical grinding) with transition elements or oxides showed relatively high hydriding and dehydriding rates when the content of additives was about 20 wt%. Ni (expected to increase hydriding and dehydriding rates) was chosen as transition element to be added. Fe₂O₃ (expected to increase hydriding rate) was selected as an oxide to be added. Ti was also selected since, it was considered to increase the hydriding and dehydriding rates by forming Ti hydride. A sample, Mg–14Ni–3Fe₂O₃–3Ti, was prepared by reactive mechanical grinding and its hydrogen storage properties were investigated. This sample absorbed 4·02 wt% H for 5 min, 4·15 wt% H for 10 min and 4·42 wt% H for 60 min at n?=?2. It desorbed 2·46 wt% H for 10 min, 3·98 wt% H for 30 min and 4·20 wt% H for 60 min at n?=?2.     

Study on the efficiency of nanosized magnetite and mixed ferrites in magnetic hyperthermia

Magnetic materials, which have the potential for application in heating therapy by hyperthermia, were prepared. This alternative treatment is used to eliminate cancer cells. Magnetite, magnesium–calcium ferrites and manganese–calcium ferrites were synthesized by sol–gel method followed by heat treatment at different temperatures for 30 min in air. Materials with superparamagnetic behavior and nanometric sizes were obtained in all the cases. Thus, these nanopowders may be suitable for their use in human tissue. The average sizes were 14 nm for magnetite, 10 nm for both Mg_0.4Ca_0.6Fe₂O₄ and Mg_0.6Ca_0.4Fe₂O₄ and 11 nm for Mn_0.2Ca_0.8Fe₂O₄. Taking into account that the Mg_0.4Ca_0.6Fe₂O₄ and Mg_0.6Ca_0.4Fe₂O₄ treated at 350 °C showed the lower coercivity values, these nanoparticles were selected for heating tests and cell viability. Heating curves of Mg_0.4Ca_0.6Fe₂O₄ subjected to a magnetic field of 195 kHz and 10 kA/m exhibited a temperature increase up to 45 °C in 15 min. A high human osteosarcoma cell viability of 90–99.5 % was displayed. The human osteosarcoma cell with magnesium–calcium ferrites exposed to a magnetic field revealed a death cell higher than 80 % in all the cases.     

Phase- and size-controllable synthesis with efficient photocatalytic activity of ZnS nanoparticles

We report a simple solution-based method to synthesize phase- and size-controllable ZnS nanoparticles at low temperature. Cubic ZnS (c-ZnS) and hexagonal ZnS nanoparticles (h-ZnS) were obtained by heating an aqueous solution of Zn(NO₃)₂·6H₂O and Na₂S₂O₃·5H₂O at different temperatures. When the system was heated at 65 °C for 24 h, hexagonal crystal structure of ZnS nanoparticles, with size of 50–350 nm, was obtained, as confirmed by X-ray diffraction and selected-area electron diffraction. When the reaction temperature was 100 °C under hydrothermal condition, c-ZnS nanoparticles were obtained and exhibited monodisperse nanoparticles with average size of 4 nm. Proper rate of S releasing tuned by the variation of pH value is believed to be critical to stabilize the hexagonal ZnS nanoparticles. Compared with large size of h-ZnS nanoparticles, c-ZnS nanoparticles show higher photocatalytic activity in degrading methyl orange (MO). The degradation efficiency of c-ZnS nanoparticles reaches 97% under UV irradiation for 120 min. The good ultraviolet absorbing ability, charge separation property, and large surface area of c-ZnS nanoparticles are believed to have a positive impact on improving the degradation rate and degradation efficiency of MO.     

Investigation of physicochemical and tribological properties of transparent oxide semiconducting thin films based on Ti-V oxides

In this paper investigations of structural and optical properties of nanocrystalline Ti-V oxide thin films are described. The films were deposited onto Corning 7059 glass using a modified reactive magnetron sputtering method. Structural investigations of prepared Ti-V oxides with vanadium addition of 19 at. % revealed amorphous structure, while incorporation of 21 and 23 at. % of vanadium resulted in V₂O₅ formation with crystallites sizes of 12.7 and 32.4 nm, respectively. All prepared thin films belong to transparent oxide semiconductors due to their high transmission level of ca. 60–75 % in the visible light range, and resistivity in the range of 3.3·10²–1.4·10⁵ Ωcm. Additionally, wettability and hardness tests were performed in order to evaluate the usefulness of the films for functional coatings.     

Effect of copper doping on structural,optical and electrical properties of Cd0·8Zn0·2S films prepared by chemical bath deposition

Cd _0·8Zn _0·2S:Cu films of 1 ·3–6 ·1 mole percentage of copper have been grown on mica substrate by using chemical bath deposition technique. The films have been characterized by using XRD, SEM and UV spectrophotometer. X-ray diffraction studies have shown that the films are polycrystalline. The average crystallite size as measured from XRD data is in the range of 125–130 nm. The activation energies of Cd _0·8Zn _0·2S:Cu films, as observed from d.c. conductivity studies in the temperature range (77–300 K) studied, decreased with the increase in Cu concentration. The optical absorption studies have revealed that the energy gap increases gradually with an increase in Cu concentration, whereas conductivity studies have shown an anomalous increase in conductivity in films of 3 ·8 mole percentage of Cu. SEM pictures have revealed the presence of defects with spherical structure having fibre network. The variation of electrical conductivity is explained based on the defects present and by adopting tunneling mechanism.     

Synthesis of thorn-like Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>·H<Subscript>2</Subscript>O by hydrothermal method

Thorn-like polycrystalline Ca₂B₂O₅·H₂O microspheres with nano-sized slices were synthesized using boric acid and calcium hydroxide as reactants by a facile catalyst-free hydrothermal method at low temperature. The products were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern reveals that the Ca₂B₂O₅·H₂O is a monoclinic phase polycrystalline with cell parameters a = 0·6702, b = 0·5419 and c = 0·3558 nm. SEM also reveals that the monoclinic phase polycrystalline are thorn-like microspheres composed of many flakes with an average thickness of <100 nm. Possible reaction and growth mechanism were also discussed.     

The effects of different precipitant agents on the formation of alumina-magnesia composite powders as the magnesium aluminate spinel precursor

Al₂O₃/MgO composite powders were synthesized via a partially wet chemical method. The effects of precipitant agent on the morphology, size and chemical composition of the resultant powders were investigated. The structures of rod-like with polygonal prism surface, platelet-like and uniform spherical Mg-compound particles were successfully prepared by using ammonium hydrogen carbonate, sodium hydroxide and ammonia water as precipitant agents, respectively. Analysis results proved that using ammonium hydrogen carbonate as precipitant agent produced nesquehonite (MgCO₃·3H₂O) Mg-compounds but in the case of other two precipitant agents, Mg-compound particles with magnesium hydroxide (Mg(OH)₂) chemical composition were obtained. The morphological features of MgO particles in Al₂O₃/MgO composite powders were the same as individual Mg-compound particles. Furthermore, conversion of the Al₂O₃/Mg-compound precursor synthesized with ammonia water to pure magnesium aluminate spinel particles was studied. The precursor converted to pure magnesium aluminate spinel phase with 220?nm particle size at 1200?°C.