Precipitation in solution-treated aluminium–4 wt% copper under cyclic strain

Solution-treated Al–4 wt% Cu was strain-cycled at ambient temperature and above, and the precipitation and deformation behaviours investigated by TEM. Anomalously rapid growth of precipitates appears to have been facilitated by a vacancy super-saturation generated by cyclic strain and the presence of continually refreshed dislocation density to provide heterogeneous nucleation sites. Crystallographic texture appears to be responsible for latent hardening in specimens tested at room temperature. Increasing temperatures lead to a gradual hardening throughout life due to precipitation. Specimens machined at 45° from the rolling direction, which exhibit rapid precipitation hardening, show greater texture hardening due to increased axial stress required to cut precipitates in specimens. In the temperature range 100–200°C, precipitation of Θ″ is suppressed by cyclic strain, and precipitation of Θ′ promoted. The rapid growth of precipitates generated by cyclic strain operates with diminishing effect at higher temperatures due to faster recovery of non-equilibrium vacancy concentrations. Θ′ precipitates generated under cyclic strain are smaller and more finely dispersed than those produced via quench-ageing due to heterogeneous nucleation on dislocations and possess a low aspect ratio and rounded edges of the broad faces caused by the introduction of ledges into the growing precipitates by dislocation cutting. Frequency effects indicate that dislocation action is responsible for the observed reduction in aspect ratio. Accelerated formation of grain-boundary precipitates appears partially responsible for rapid inter-granular fatigue failure at elevated temperatures, resulting in coexistent fatigue striations and ductile dimples on the fracture surface.     

Cyclic deformation and fatigue cracking behaviour of polycrystalline Cu,Cu–10 wt% Zn and Cu–32 wt% Zn

The cyclic deformation behaviour of polycrystalline Cu, Cu–10 wt% Zn and Cu–32 wt% Zn was systematically investigated in the plastic strain amplitude range of 1 × 10^?4–4 × 10^?3. The differences in the cyclic stress–strain (CSS) responses and fatigue cracking behaviour between Cu, Cu–10 wt% Zn and Cu–32 wt% Zn were compared. It was found that the occurrence of a cyclic saturation for Cu–10 wt% Zn and Cu–32 wt% Zn strongly depends on the applied strain amplitude, whereas polycrystalline Cu always displays cyclic saturation. Surface deformation morphologies were analyzed by scanning electron microscopy (SEM). One of the major features observed is that the slip bands become increasingly homogenous with Zn addition. The fatigue cracks were found to frequently nucleate along the annealing twin boundaries (TBs) in Cu–10 wt% Zn and Cu–32 wt% Zn, but not in polycrystalline Cu. Based on these experimental results, the cyclic deformation response and fatigue cracking behaviour are discussed, and a developed TB cracking mechanism is proposed to explain the difference in fatigue cracking mechanisms in Cu, Cu–10 wt% Zn and Cu–32 wt% Zn.     

In situ analysis of the tensile deformation mechanisms in extruded Mg–1Mn–1Nd (wt%)

An extruded Mg–1Mn–1Nd (wt%) (MN11) alloy was tested in tension in an SEM at temperatures of 323?K (50°C), 423?K (150°C), and 523?K (250°C) to analyse the local deformation mechanisms through in situ observations. Electron backscatter diffraction was performed before and after the deformation. It was found that the tensile strength decreased with increasing temperature, and the relative activity of different twinning and slip systems was quantified. At 323?K (50°C), extension twinning, basal, prismatic ?a?, and pyramidal ?c?+?a? slip were active. Much less extension twinning was observed at 423?K (150°C), while basal slip and prismatic ?a? slip were dominant and presented similar activities. At 523?K (250°C), twinning was not observed, and basal slip controlled the deformation.     

Effect of copper addition on some properties of rapidly solidified lead-free Sn–-10 wt% Zn alloys

This study aimed at investigating the effect of adding copper (Cu) on some properties of the lead-free alloys which rapidly solidified from melt. X-ray analysis, hardness, elastic modulus, electrical conductivity and resistivity were studied. The results indicated that the alloy hardness and elastic modulus improved by increasing the copper (Cu) content and decreasing the zinc (Zn) content. The electrical conductivity ranged from 0.250 to 0.847?×?10⁷ ohm^?1 m^?1 for the alloy under study. The electrical resistivity increases linearly with temperature until the melting point is reached. The residual resistivity results from disturbances in the lattice rather than caused by thermal vibration and the most drastic increases in the residual resistivity are caused by foreign atoms in solid solution with matrix metal. The electrical resistivity values ranged from 11.8 to 40?×?10^?8 ohm m, when the copper content changed from 0.0 to 2.0 wt% and zinc changed from 8.0 to 10.0 wt%.     

Interpretation of the change in optical constants of different compositions of Ge–Se–In in terms of cohesive energy

Compositional dependencies of the optical and physical properties of as-deposited amorphous Ge_xSe_90?xIn₅ films (with 5≤x≤30 at%), prepared by thermal evaporation have been studied. The optical energy gap $E_g^{opt}$ is derived from Tauc's extrapolation in the strong absorption region in terms of transmission and reflection spectra. The relationship between the optical gap and chemical composition of the Ge_xSe_90?xIn₅ (with 5≤x≤30 at%) amorphous system is discussed in terms of the chemical bond approach. The refractive index, n and film thickness, d have been determined by an envelope method using transmission spectra. It is observed that the refractive index, n of Ge_xSe_90?xIn₅ thin films increases with increasing x, over the entire spectral range, which is related to both the increased density and average coordination number.     

Consequences of the center–of–mass correction in nuclear mean–field models

We study the influence of the scheme for the correction for spurious center–of–mass motion on the fit of effective interactions for self–consistent nuclear mean–field calculations. We find that interactions with very simple center–of–mass correction have significantly larger surface coefficients than interactions for which the center–of–mass correction was calculated for the actual many–body state during the fit. The reason for that is that the effective interaction has to counteract the wrong trends with nucleon number of all simplified schemes for center–of–mass correction which puts a wrong trend with mass number into the effective interaction itself. The effect becomes clearly visible when looking at the deformation energy of largely deformed systems, e.g. superdeformed states or fission barriers of heavy nuclei. Received: 6 September 1999     

Origin of tweed in Au–Cu–Al alloys

The premartensitic tweed in Au–Cu–Al alloys, contrary to previous thought that resort to defects, is confirmed to be associated with the coherent embryos of an intermediate phase (I phase) embedded in parent phase. The parent?→?I phase transformation temperature was measured by differential scanning calorimeter and dynamic mechanical analysers, which shifts from 82.3 to 557.6?°C depending on the alloy composition. X-ray diffraction and transmission electron microscopes (TEM) results show that the parent?→?I phase transformation is a charge density wave transition that cannot be suppressed even by melt-spun method, which shows obvious compositional inhomogeneity between I phase and parent. The results imply that the parent?→?I phase transition is a fast displacive transformation coupled with diffusion. Moreover, accompanying the parent?→?I phase transformation, alloys demonstrate diversified microstructure revealed by TEM observation, from tweed to chessboard nanowires or twins. These findings provide the experimental evidence for that parent?→?I phase transformation in Au–Cu–Al alloys is originated from pseudospinodal decomposition as theoretically predicted.     

Simulation of cascades in tungsten–helium

Helium (He) is present in fusion reactor wall materials, and its effect on radiation damage must be taken into account. The effect of He on displacement cascades in tungsten (W) has been studied using molecular dynamics simulations. Three different W–W potentials were compared and found to differ, especially for the clustering of the vacancies formed in the cascades. While there are differences in the amounts of damage depending on the potential, the overall effect of He in interstitial positions was to increase the amount of damage, while He in substitutional positions reduces it, due to the effect He has on the recombination of tungsten interstititals.     

Study of Yang–Mills–Chern–Simons theory in presence of the Gribov horizon

The two-point gauge correlation function in Yang–Mills–Chern–Simons theory in three dimensional Euclidean space is analysed by taking into account the non-perturbative effects of the Gribov horizon. In this way, we are able to describe the confinement and de-confinement regimes, which naturally depend on the topological mass and on the gauge coupling constant of the theory.     

Fracture toughness evaluation of WC–10 wt% Co hardmetal sintered under high pressure and high temperature

This work focused on fracture toughness studies of WC–10?wt% Co hardmetal fabricated through the high pressure/high-temperature technique. A powder mixture of WC–10?wt% Co was sintered at 1500–1900°C under a pressure of 7.7?GPa for 2 and 3?min. Vickers hardness test at two different loads of 15 and 30?kgf was done and fracture toughness of the sintered bodies was measured using the indentation method to obtain the effect of sintering parameters. Structural analyses were also performed via X-ray diffraction to investigate structure-related properties. Full density was achieved for high sintering temperature along with abnormal grain growth that reduced hardness. High hardness was observed ranging from 1200 to 1670?HV and fracture toughness increased with increasing sintering temperature up to the highest value of 17.85?MPa/m^1/2.     

Microscopic theory of dipole–dipole interaction in ensembles of impurity atoms in a Fabry–Perot cavity

We develop a consistent quantum theory of the collective effects that take place when electromagnetic radiation interacts with a dense ensemble of impurity centers embedded in a transparent dielectric and placed in a Fabry–Perot cavity. We have calculated the spontaneous decay dynamics of an excited impurity atom as a specific example of applying the developed general theory. We analyze the dependence of the decay rate on the density of impurity centers and the sample sizes as well as on the characteristic level shifts of impurity atoms caused by the internal fields of the dielectric. We show that a cavity can affect significantly the pattern of collective processes, in particular, the lifetimes of collective states.     

Effects of oxidation of DyH_3 in Nd–Fe–B sintered magnets

The effects of oxidation of Dy H3 with respect to dysprosium addition to Nd–Fe–B sintered magnets are examined.Samples sintered with the addition of freshly milled dysprosium hydride, dysprosium hydride exposed to air at room temperature for 15 min and dysprosium hydride exposed to air at 100°C for 3.5 hours are studied from the aspects of magnetic properties, microstructures, and their degradation, respectively. It is found that some oxidized dysprosium is distributed in the Nd-rich phase; hence, the decrease of remanence occurred. The degradation results indicate that preoxidised dysprosium can be a major factor in increasing the corrosion rate. The microstructures and corrosion acceleration test suggested that the oxidation is detrimental to remanence.     

First principles study of interactions of oxygen–carbon–vacancy in bcc Fe

Behaviors of C or O in bcc Fe and interactions of C–O and oxygen–carbon–vacancy(O–C–□) are investigated by first principles calculations. Octahedral interstitial site is the most stable position for an O atom in bcc Fe. The migration energy of an O atom in bcc Fe is 0.46 eV. The strength of O–Fe(1 nn) bond(0.32) is slightly greater than that of Fe–Fe metallic bond(0.26). Repulsive interactions of C–C, O–O, and C–O exist in bcc Fe. When the concentration of FIA(FIA refers to C or O) is relatively high, a vacancy can attract four FIAs and form stable FIAs–□ complex.     

Formulation of Leggett–Garg Inequalities in Terms of q-Entropies

As is well known, the macroscopic realism and the noninvasive measurability together lead to Leggett–Garg inequalities violated by quantum mechanics. We consider tests of the Leggett–Garg type with use of the q-entropies.For all q≥1, quantum mechanics predicts violations of an entire family of q-entropic inequalities of the Leggett–Garg type. Violations are exemplified with a quantum spin-s system. In general, entropic Leggett–Garg inequalities give only necessary conditions that some probabilistic model is compatible with the macrorealism in the broader sense. The presented q-entropic inequalities allow to widen a class of situations, in which an incompatibility with the macrorealism can be tested. In the considered example, both the strength and range of violations are somehow improved by varying q.We also examine q-entropic inequalities of the Leggett–Garg type in the case of detection inefficiencies, when the no-click event may occur in each observation. With the use of the q-entropic inequalities, the required amount of efficiency may be reduced.     

Tool measurements of thunderstorms in Yakutia in 2003–2006

We propose a technique for tool measurement of the lightning-discharge density in Yakutia in 2003–2006 by the radiophysical method using one- and two-point lightning detectors. The observed features of the spatio-temporal distribution and the parameters of thunderstorm cores are discussed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 10, pp. 825–829, October 2008.     

Biham–Middleton–Levine model in consideration of cooperative willingness

In this paper, the Biham-Middleton-Levine （BML） model with consideration of cooperative willingness has been proposed to study the traffic flow in urban networks. An evolutionary game with a cooperative willingness profile is intro-duced to deal with conflicts between disturbing neighbors. Simulation results suggest that imitating cooperative willingness can ease the effect of premature seizure on traffic flow due to the introduction of evolutionary games. Phase diagrams with a strategy profile and cooperative willingness profile have been investigated in detail. Our findings also prove that by imitating the more successful, cooperative willingness instead of simply the more successful strategies, the evolution of cooperation is significantly promoted, hence improving the order of cooperation and relieving the pressure of traffic networks.     

Influence of aluminum doping in Li–Co–Ti ferrite

The crystallographic and magnetic properties of low aluminum doped lithium cobalt titanium ferrites, Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄(0.0≤x≤0.5), in the scope of spinel structure and ferrimagnetic property were investigated. Ferrites were doped with aluminum in the range of 0.0–0.5 and were synthesized by using the conventional ceramic methods. Using X-ray diffraction and Mössbauer spectroscopy, we confirmed the formation of crystallized particles. All of the samples showed a single phase with a spinel structure, and the lattice parameters linearly decreased as the doped aluminum content was increased. The particle size of the samples also decreased as the doped aluminum content increased. Until x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄, the Mössbauer spectra could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra of Fe³⁺ with A- and B-sites. However, for x=0.5, the Mössbauer spectrum could be fitted with two Zeeman sextets and one doublet. From the variation of the Mössbauer parameters and the absorption area ratio, the cation distributions were determined. The magnetic behavior of the samples showed that an increase in the aluminum contents led to a decrease in the saturation magnetization, whereas the coercivity decreased until x=0.4 and then increased. The minimum coercivity was 52.4 Oe at x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄.     

Universality of the Mott–Ioffe–Regel limit in metals

The absence of resistivity saturation in many strongly correlated metals, including the high-temperature superconductors, is critically examined from the viewpoint of optical conductivity measurements. Coherent quasiparticle conductivity, in the form of a Drude peak centred at zero frequency, is found to disappear as the mean free path (at ω?=?0) becomes comparable with the interatomic spacing. This basic loss of coherence at the so-called Mott–Ioffe–Regel (MIR) limit suggests that the universality of the MIR criterion is preserved even in the presence of strong electron correlations. We argue that the shedding of spectral weight at low frequencies, induced by strong correlation effects, is the primary origin of the extended positive slope of the resistivity to high temperatures observed in all so-called ‘bad metals’. Moreover, in common with those metals which exhibit resistivity saturation at high temperatures, the scattering rate itself, as extracted from optical spectra, saturates at a value consistent with the MIR limit. We consider possible implications that this ceiling in the scattering rate may have for our understanding of transport within a wide variety of bad metals and suggest a better method for analysing their optical response.     

Influences of ultrasonic- and microwave-irradiated preparation methods on the structural and dielectric properties of (PEO–PMMA)–LiCF3SO3–x wt% MMT nanocomposite electrolytes

Ionics - The novel solid polymeric nanocomposite electrolytes (SPNEs) consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend with lithium triflate (LiCF3SO3) as ionic...     

Rates of Convergence in the Blume–Emery–Griffiths Model

We derive rates of convergence for limit theorems that reveal the intricate structure of the phase transitions in a mean-field version of the Blume–Emery–Griffith model. The theorems consist of scaling limits for the total spin. The model depends on the inverse temperature $\beta $ and the interaction strength $K$ . The rates of convergence results are obtained as $(\beta ,K)$ converges along appropriate sequences $(\beta _n,K_n)$ to points belonging to various subsets of the phase diagram which include a curve of second-order points and a tricritical point. We apply Stein’s method for normal and non-normal approximation avoiding the use of transforms and supplying bounds, such as those of Berry–Esseen quality, on approximation error.