Low cycle fatigue behavior of zirconium–titanium–steel composite plate

The low cycle fatigue behavior of zirconium–titanium–steel composite plate under symmetrical and asymmetric stress control was studied. The effects of mean stress and stress amplitude on cyclic deformation, ratcheting effect and damage mechanism were discussed in detail. The results show that under symmetric stress control, the forward ratcheting deformation is observed. Under asymmetric stress control, the ratcheting strain increases rapidly with mean stress and stress amplitude increasing. Under high stress amplitude, the influence of mean stress is more significant. In addition, by studying the variation of strain energy density, it is found that the stress amplitude mainly promotes the fatigue damage, while the mean stress leads to the ratcheting damage. In addition, fracto- graphic observation shows that the crack initiates in the brittle metal compound at the interface, and the steel has higher resistance to crack propagation. Finally, the accuracy of life prediction model considering ratcheting effect is discussed in detail, and a high-precision life prediction model directly based on mean stress and stress amplitude is proposed.     

Preparation and corrosion resistance of titanium–zirconium–cerium based conversion coating on 6061 aluminum alloy

This paper aims to develop a chromium-free chemical conversion coating with good corrosion resistance. A novel chemical conversion coating was prepared on 6061 aluminum alloy by dipping in the treatment solution containing titanium/zirconium based-ions and sodium metaphosphate and cerium nitrate hexahydrate as additives. The morphology and composition of the conversion coatings were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The microarea structure of conversion coatings at different formation stages was analyzed by electron probe microanalyzer. The electrochemical polarization curve revealed that the corrosion potential of the conversion coating was −0.577 V and the corrosion current density was 0.1148 μA/cm². The equivalent circuit fitted by AC impedance showed that the film resistance reaches 68,140 Ω. The formation of coating preferentially grows on the Al (Fe) Si intermetallic to form oxides of Ti and Zr; then TiO₂ formed by a higher concentration of Ti⁴⁺ gradually covered ZrO₂. Ce³⁺ could adsorb on the intermetallic compound, the hydrolysis of which causes the local pH of the solution to decrease and promotes the aluminum alloy dissolved.     

Electrochemical synthesis of novel conducting polymer composite: Polypyrrole–pentacyanonitrosylferrate

With a view to develop conducting polymer film of high electroactivity, pentacyanonitrosylferrate (PCNFe) doped polypyrrole (PPY) composite films are prepared using cyclic voltammetry deposition method. The PPY–PCNFe composite is characterized by FTIR, TEM and TGA analysis. The electroactivity of PPY–PCNFe composite film is studied in 3 mM KCl (common electrolyte) solution. Two redox pairs at E_1/2 = ?0.59 V and 0.02 V due to redox behavior of polymer and dopant anions respectively are observed. The electroactivity study reveals the existence of two types of PCNFe dopant anions in the polymeric film: one form is loosely held and prone to easy removal from the polymer matrix whereas the other form is strongly bound to polymer backbone and prone to electrochemical redox reaction by movements of electrons. The high electroactivity of the film is attributed to the movements of ionic species into and out of the polymeric film as well as movements of electron.     

Formation and properties of nano- and micro-structured conducting polymer host–guest composites

Process of formation of polyaniline (PANI) at the surface of SiC and CdS nanoparticles or submicron- and micron-sized particles of poly(vinylidene fluoride) (PVDF), polycarbonate and polyamides-11, 12 and properties of the prepared composites are considered. Beginning of the formation of the PANI shell at the particle surface was evaluated. This important result opens the possibility to control properties of the final hybrid composite. In case of CdS nanoparticles PANI was synthesized in the form of nanofibers embedding these nanoparticles. Films of the PANI–polymer composites showed the conductivity of up to ～0.4 S/cm. The planar heterojunction of the compression molded PVDF/PANI–DBSA film with bulk CdS displayed photovoltaic activity.     

The preparation and characterization of the cross-linked Ag–AgCl/polypyrrole nanocomposite

The cross-linked Ag–AgCl/polypyrrole (PPy) nanocomposite was synthesized using silver nanowires as templates. In the process, FeCl₃ served not only as the oxidant for pyrrole monomer but also as the etching-agent for silver nanowires. The morphologies of the product were observed by transmission electron microscopy. The existence of silver chloride and silver in PPy matrix was confirmed by X-ray diffraction and X-ray photoelectron spectroscope technologies. A possible formation mechanism of the cross-linked Ag–AgCl/PPy nanocomposite was also discussed.     

The effects of nanoparticle addition on SiC and AlN powder–polymer mixtures: Packing and flow behavior

The development of methods to increase sintered density and improve dimensional tolerances is a crucial issue in powder metallurgy and ceramic processing. Increasing the packing density of starting powders is one effective route to achieve high sintered density and dimensional precision. The current paper presents an in-depth study on the effect of nanoparticle addition on the powder content of SiC and AlN powder–polymer mixtures. In particular, bimodal mixtures of nanoscale and sub-micrometer particles were found to have significantly increased powder volume fraction (solids loading) in the mixtures for injection molding. This observation to increasing packing density by using nanoparticles is surprising and novel since nanoparticles are known to inherently exhibit poor packing behavior. Additionally, for a given volume fraction of powder, the bimodal μ-n suspensions had a lower viscosity at any shear rate compared to the monomodal μ-suspensions. The ability to lower the suspension viscosity by adding nanoparticles to micron-sized particles has important implications for processing of particulate suspensions by powder injection molding (PIM), extrusion, slip casting and tape casting. Samples made from bimodal powders exhibited slower polymer removal during debinding and higher densification with lower shrinkage on sintering compared to the corresponding samples made from monomodal powder mixtures.     

Structure and properties of micro-arc calcium phosphate coatings on pure titanium and Ti–40Nb alloy

The microstructure, physical and mechanical, and chemical properties of micro-arc calcium phosphate (CaP) coatings deposited under different process voltages in the range of 150–400 V on the commercially pure titanium (Ti) and Ti–40%Nb (Ti–40Nb) (mass fraction) alloy were investigated by the SEM, TEM, XRD and EDX methods. The coating thickness, roughness, and sizes of structural elements were measured and showed similar linear character depending on the process voltage for the coatings on both substrates. SEM results showed the porous morphology with spherical shape structural elements and rough surface relief of the coatings. XRD and TEM studies exhibited the amorphous structure of the CaP coating. With increasing the process voltage to 300–400 V, the crystalline phases, such as CaHPO₄ and β-Ca₂P₂O₇, were formed onto the coatings. The annealing leads to the formation of complex poly-phase structure with crystalline phases: CaTi₄(PO₄)₆, β-Ca₂P₂O₇, TiP₂O₇, TiNb(PO₄)₃, TiO₂, NbO₂, and Nb₂O₅. The applied voltage and process duration in the ranges of 200–250 V and 5–10 min, respectively, revealed the coating formed on Ti and Ti–40Nb with optimal properties: thickness of 40–70 μm, porosity of 20%–25%, roughness (R_a) of 2.5–5.0 μm, adhesion strength of 15–30 MPa, and Ca/P mole ratio of 0.5–0.7.     

Microstructure, properties and oxidation behavior of the glass-ceramic based coating on near-α titanium alloy

Protective SiO₂-Al₂O₃-CaO-Na₂O glass-ceramic based coating produced on TIMETAL 834 by slurry technique was investigated. Analytical scanning and transmission electron microscopy as well as X-ray diffraction were used for detailed analyses of a microstructure and chemical composition of the coating. It was found that the coating contains crystalline phases: CaSiO₃, NaAlSiO₄, Na₂CaSiO₄ and amorphous phase containing mainly O, Si and Al. It was established that glass-ceramic coating formed on TIMETAL 834 essentially improves the alloy selected properties, e.g. its hardness and high temperature oxidation resistance.     

Polyaniline–poly(vinyl alcohol) conducting composite: material with easy processability and novel application potential

The present work reports an easy route for synthesis of polyaniline (PAn) in stable aqueous solution/dispersion form, using poly(vinyl alcohol) (PVA) as an efficient steric stabilizer. Resulting composite successfully combines desirable physical properties like mechanical strength, solution processibility and electrical conductivity of PVA and PAn components. The composite was subjected to versatile characterizations and its different physical properties (especially optical, thermal, mechanical and electrical) were explored. Free standing films can be obtained from the solutions, which exhibit important microwave shielding property over the X-band. This has enhanced the importance of this material to a large extent.     

Synthesis and characterization of polyaniline–Fe3O4 nanocomposite: Electrical conductivity,magnetic, electrochemical studies

Fe₃O₄ nanoparticles were prepared by hydrolysis reaction of urea in ethylene glycol as solvent at 160 °C. The prepared Fe₃O₄ nanoparticles were incorporated into polyaniline (PANI) matrix during in situ chemical oxidative polymerization of aniline with different molar ratios of aniline:Fe₃O₄ (19:1, 16:1, 12:1, 9:1) using (NH₄)₂S₂O₈ as oxidant in aqueous solution of sodium dodecylbenzene sulphonic acid under N₂ atmosphere. Room temperature conductivities of the synthesized PANI, PANI/Fe₃O₄ (19:1) and PANI/Fe₃O₄ (9:1) are 3.2 × 10^?4, 1.8 × 10^?5 and 1.0 × 10^?5 S/cm, respectively, indicating decrease of conductivity with increase of Fe₃O₄ in PANI. Saturation magnetizations of Fe₃O₄, PANI/Fe₃O₄ (19:1), and PANI/Fe₃O₄ (9:1) are 27.5, 5.5 and 6.3 emu/g, respectively, indicating an increase of ferromagnetic interaction with more incorporation of Fe₃O₄ in PANI matrix, whereas PANI is diamagnetic. Electrochemical studies shows that Zn-PANI/Fe₃O₄ (9:1) battery had delivered maximum discharge capacity (78.6 mAh/g) as compared to Zn-PANI battery (50.1 mAh/g) at constant current of 0.5 mA cm^?2. At constant resistance of 1000 Ω, discharge capacities of Zn-PANI/Fe₃O₄ and Zn-PANI battery are 73.37 and 50.8 mAh/g, respectively.     

Polyaniline synthesis with iron(III) chloride–hydrogen peroxide catalyst system: Reaction course and polymer structure study

We report on the catalytic polymerization of aniline (ANI) with FeCl₃/H₂O₂ system, which can considerably lower contamination of neat polyanilines (PANIs) by side-products characteristic of stoichiometric polymerization. However, catalytically prepared PANIs exhibit reduced conductivity related most probably to side reactions involving radicals generated as integral components of the FeCl₃/H₂O₂ system. Catalytic polymerization of ANI with FeCl₃/H₂O₂ system was found to be the reaction of approximately 2nd order with respect to ANI and gives PANIs of a good quality only when [H₂O₂] in the reaction mixture was kept low, i.e., at under-stoichiometric ratios [H₂O₂]/[ANI]. At over-stoichiometric ratio [H₂O₂]/[ANI], PANIs of lowered conductivity, worse spectroscopic characteristics and increased size of PANI nanostructures were obtained; nevertheless, these PANIs were not over-oxidized to pernigraniline state. The reaction-time profiles of the open-circuit potential of reaction mixtures exhibited an inflection related to the H₂O₂ depletion from the system. Total consumption of H₂O₂ exceeded its consumption necessary on ANI polymerization, which proves partial decomposition of H₂O₂ by Fe ions. UV/vis and resonance Raman spectra indicate incomplete deprotonization of PANIs prepared with FeCl₃/H₂O₂ system and subsequently treated with aqueous ammonia, which proves partial self-doping of these PANIs. However, IR and NMR spectra indicate rather low extent of self-doping. It has been proposed that self-doping of PANI involves phenolic OH groups originated from side reactions involving radical species formed from H₂O₂.     

Synthesis,characterization, electrical transport and magnetic properties of PEDOT–DBSA–Fe3O4 conducting nanocomposite

Electrical transport and magnetic properties of newly synthesized conducting polymer nanocomposites involving poly(3,4-ethylenedioxythiophene) (PEDOT) and Fe₃O₄ nanoparticles are studied. Nanocomposite samples of varying proportions of inorganic to organic components were synthesized by adding EDOT monomer stabilized in miceller solution of DBSA (dodecylbenzene sulphonic acid) to aqueous colloidal dispersion of Fe₃O₄ nanoparticles, followed by oxidative polymerization using ammonium peroxodisulphate (APS). Transmission electron microscopic (TEM) photographs show presence of distinct spherical Fe₃O₄ naonparticles having diameter range of 20–40 nm and they are incorporated within the polymer chain in the nanocomposite samples. Temperature-dependent DC conductivity analysis indicates a smooth cross-over of the charge conduction from the high temperature 3D Mott's variable range hopping (VRH) mechanism to the 2D ES (Efros and Shklovoskii)-VRH behaviour at low temperature. Temperature-dependent DC magnetization studies reveal enhancement of blocking temperature (T_B) in the nanocomposite samples compared to that of bare Fe₃O₄ nanoparticles. Core shell morphology of the nanoparticles seems to be the cause for lowering the value of saturation magnetization of the Fe₃O₄ nanoparticles. Estimated magnetic domain sizes are comparable to those of grain sizes for the nanocomposite samples having lower content of nanoparticles (P₅₀ and P₁₀₀). Temperature-dependent AC-susceptibility data also supports the superparamagnetic behaviour.     

A study of the relationship between the electrochemical behavior of magnesium–lithium alloys in phosphate media and their phosphating treatment

The electrochemical behavior of magnesium–lithium alloys of MA 21 and IMV 12 types in the solutions of moderately acidic phosphates (0.34 M H₃PO₄ + 0.17 M HNO₃ + NaOH, pH 2.7) containing fluoride ions (0.01–0.09 mol/L)) is studied in the context of phosphating treatment. The relationship of the results of electrochemical studies with the results of phosphating of the given alloys is determined. The dependence of the electrochemical activity of alloys on their nature is shown. The rate of stationary electrochemical process determines the rate of the formation of phosphate films with modified properties and structure on magnesium–lithium alloys.     

Structural investigations of Fe–Ga alloys: Phase relations and magnetostrictive behavior

The underlying relation between the magnetostriction (3/2) λ₁₀₀ and Ga concentration for Fe–Ga alloys is an open question. This work presents a systematic structural study of the structure-property dependence of Fe–Ga alloys by transmission electron microscopy and X-ray diffraction. Results show that in the regions where monotonic increases in (3/2) λ₁₀₀ are exhibited, single-phase A2 or D0₃ is found for the slow-cooled alloys. For the alloys in the range 18–21 at.% Ga, quenching extends the single-phase A2 to higher Ga concentrations, thereby continuing to enhance magnetostriction. The sudden decrease in (3/2) λ₁₀₀ near Fe–19 at.% Ga as well as Fe–29 at.% Ga was associated with the formation of phase mixtures. For quenched alloys between 25 and 29 at.% Ga, a phase mixture of (A2 + B2 + D0₃) was found, but the presence of this phase mixture does not seem to have a large effect on magnetostriction.     

Electrical conductivity of polyaniline–dodecylbenzene sulphonic acid complex: thermal degradation and its mechanism

Polyaniline (PANI) doped with dodecylbenzene sulphonic acid (DBSA) and methylbenzene sulphonic acid (MBSA) were used as model compounds to investigate thermal degradation mechanisms of electrical conductivity of PANI salts. The effects of high temperature annealing on the conductivity, thermal stability and morphology of the doped PANI were studied. Within a period of 2 h, the conductivity of the two PANI salts decreases continuously with the annealing time. The conductivity reduction also increases significantly with the annealing temperature. Both polymers show significant weight loss during the annealing, especially at 200 °C. The weight loss of PANI–MBSA is more pronounced than that of PANI–DBSA, while the conductivity reduction shows an opposite trend. Scanning electronic microscopy (SEM) study reveals a significant morphology change caused by the annealing. Fourier transformed infrared (FT-IR) results indicate that some dopants are converted to free acids due to the annealing. It is, therefore, suggested that in addition to cross-linking of PANI and evaporation and degradation of the dopants, the segregation of the dopants from the polymers is also an important mechanism responsible for the conductivity degradation observed.     

Young’s modulus evolution and texture-based elastic–inelastic strain partitioning during large uniaxial deformations of monoclinic nickel–titanium

The authors draw upon recent first-principles calculations of monoclinic NiTi elastic constants to develop a combined numerical–empirical, texture-based approach for calculating the Young’s modulus of polycrystalline, monoclinic nickel–titanium specimens. These calculations are carried out for load direction inverse pole figures measured in situ via neutron diffraction during tension–compression deformations to ～18% true strain, as well as unloading events. As demonstrated by application to this empirical data set, the texture-based approach results in the ability to quantify the evolution of Young’s modulus and to micromechanically partition elastic and inelastic macroscopic strains for the entirety of non-linear and asymmetric uniaxial deformations, a result that had not been achieved previously for a monoclinic material.     

Design and synthesis of a new thiophene based donor–acceptor type conjugated polymer with large third order nonlinear optical activity

In this communication we describe the design and synthesis of a new conjugated polymer (P) carrying 3,4-dialkoxythiophene, 1,3,4-oxadiazole and thienylene-vinylene units, from its monomers using Wittig condensation method. The structure of newly synthesized polymer was confirmed by FT-IR, ¹H NMR, UV–vis spectral, elemental analysis and gel permeation chromatographic techniques. The polymer exhibited good thermal stability with the onset decomposition temperature around 320 °C in nitrogen atmosphere. Further, its electrochemical, linear and nonlinear optical properties have been investigated. The optical and electrochemical band gap was found to be 2.21 eV. Its third-order nonlinear optical property was investigated by Z-scan and DFWM techniques, using a Q-switched, frequency doubled Nd:YAG laser producing 7 ns laser pulses at 532 nm. Z-scan results reveal that the polymer exhibits self-defocusing nonlinearity. The operating mechanism involves reverse saturable absorption. The polymer shows strong optical limiting behavior due to effective two-photon absorption (2PA). The value of 2PA coefficient was found to be 3.0 × 10^?11 mW, which is comparable to that of good optical limiting materials. The fluorescence quantum yield of the polymer in solution was determined using quinine sulfate as standard and it was found to be 35%.     

Flow behavior of Al–6.2Zn–0.70Mg–0.30Mn–0.17Zr alloy during hot compressive deformation based on Arrhenius and ANN models

The hot deformation behavior of Al–6.2Zn–0.70Mg–0.30Mn–0.17Zr alloy was investigated by isothermal compression test on a Gleeble–3500 machine in the deformation temperature range between 623 and 773 K and the strain rate range between 0.01 and 20 s^?1. The results show that the flow stress decreases with decreasing strain rate and increasing deformation temperature. Based on the experimental results, Arrhenius constitutive equations and artificial neural network (ANN) model were established to investigate the flow behavior of the alloy. The calculated results show that the influence of strain on material constants can be represented by a 6th-order polynomial function. The ANN model with 16 neurons in hidden layer possesses perfect performance prediction of the flow stress. The predictabilities of the two established models are different. The errors of results calculated by ANN model were more centralized and the mean absolute error corresponding to Arrhenius constitutive equations and ANN model are 3.49% and 1.03%, respectively. In predicting the flow stress of experimental aluminum alloy, the ANN model has a better predictability and greater efficiency than Arrhenius constitutive equations.