Electrical resistance,compressional strength,and extension of Ni-Mo and Ni-W alloys

An experimental study has been made of the temperature dependences of the compressional strength of Ni alloys with 5 and 10 at.% Mo and 5 at.% W, of the kinetic curves for the electrical resistance during annealing at 400 °C, and of the nature of the tensile deformation at various temperatures. The mechanism primarily responsible for the anomalous behavior of the temperature-rate dependence of the strength of these alloys may be the formation of microscopic carbide inclusions and Cottrell carbon atmospheres at dislocations during the deformation. Presence of the K state amplifies the jumps on the flow curves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 1, pp. 89–93, January, 1970.In conclusion we note that this strengthening is displayed to some extent in other systems characterized by a K state.     

EPR studies of changes in the charge state of Cr over a cross section of dislocation pipes in ZnS crystals

Short-term high-temperature annealing of ZnS crystals in a zinc atmosphere is shown to cause rapid Zn diffusion through dislocation pipes along growth-dislocation lines. As a result, the impurity ions of divalent chromium localized in Cottrell atmospheres outside Read cylinders become singly ionized. Plastic deformation of such ZnS crystals or the passing of an electric current through them under a voltage higher than a certain threshold value leads to a decrease in the number of univalent chromium ions. This decrease can be explained by an increase in the radius of Read cylinders as growth dislocations leave Cottrell atmospheres and by an increase in the linear density of their electric charge.     

Effect of dislocation density on the ageing of NaCl ∶ BaCl2 crystals

The ageing of NaCl BaCl₂ crystals deformed to different degrees has been investigated by means of electric conductivity measurements at 550°C. It has been found that the precipitation of BaCl₂ out of the lattice takes place mainly on edge dislocations. In the earliest stage of the process a Cottrell cloud is formed around the dislocations and precipitation nuclei are formed as the concentration increases. The results are in good quantitative agreement with the simple Cottrell theory.     

Computational design of UHS maraging stainless steels incorporating composition as well as austenitisation and ageing temperatures as optimisation parameters

An extended integral alloy design approach for the development of new ultra high strength maraging steels is presented, which incorporates not only chemical composition effects but also criteria accounting for the influence of the entire heat treatment. The approach considers the desired strengthening precipitates formed during the final ageing treatment as well as undesirable equilibrium phases present during the preceding high temperature homogenisation treatment. The results are compared with the predictions of a previous model, which considered the combination of composition and final precipitation tempering stage only.     

Contributions of different strengthening mechanisms to the shear strength of an extruded Mg–4Zn–0.5Ca alloy

The shear deformation behaviour of an extruded Mg–4Zn–0.5Ca alloy was studied using shear punch testing at room temperature. The extrusion process effectively refined the microstructure, leading to a grain size of 4.6 ± 1.4 μm. Contributions of different strengthening mechanisms to the room temperature shear yield stress, and overall flow stress of the material, were calculated. These mechanisms include dislocation strengthening, grain boundary strengthening, solid solution hardening and strengthening resulting from second-phase particles. Grain boundary strengthening and solid solution hardening made significant contributions to the overall strength of the material, while the contributions of second-phase particles and dislocations were trivial. The observed differences between calculated and experimental strength values were discussed based on the textural softening of the material.     

Effect of electric current on starting characteristics and activation parameters of short dislocations in Si crystals

It is shown that the passage of an electric current through crystalline silicon may lead to the so-called galvanoplasticization, as well as the galvanostrengthening, effect. It is found that the effect is sensitive to the temperature regime of deforming and to the preliminary high-temperature treatment of the samples. The motion delay time for short dislocations and starting stresses are significantly affected by the current. The relation of these effects to the change in the electric state of the Cottrell atmosphere as a result of the passage of the current through the crystal is considered.     

The influence of frequency redistribution on the transfer of gyroresonant photons in the atmospheres of compact stars: Monte-Carlo analysis

We numerically model the frequency redistribution of gyroresonant photons in a plane-parallel semi-infinite plasma atmosphere of a compact star by means of the Monte-Carlo method. We calculate the mean frequency shift and the mean number of scatterings for photons leaving the atmosphere as functions of the optical depth at emission, plasma temperature, and magnetic field strength. The probability of the escape of cyclotron-radiation photons from the atmosphere as a function of their optical depth at birth is calculated. The influence of the frequency redistribution effects on the spectrum of emergent radiation is studied.     

Reprise: partial chemical strain dislocations and their role in pinning dislocations to their atmospheres

A correct solution for a dislocation atmosphere is provided using Hirth's Standard Model, confirming the errors in Hirth and Lothe. Contrary to what is given there, concentration changes in Cottrell atmospheres reduce an edge dislocation's stress and its elastic energy, thereby reducing the magnitude of the concentration changes. The chemical and elastic strain fields from Cottrell atmospheres are again shown to behave as partial dislocations with variable Burgers vectors that are not crystal translation vectors. The reality of partial dislocations provides a simpler explanation for pinning of dislocations by atmospheres. Much of the literature on dislocation properties in solid solutions should be re-examined.     

铁磷合金中的Snoek-Kê-K?ster峰

用真空葛氏摆,研究了Fe-C+N-P合金系冷加工试样内耗。发现置换式固溶元素磷,强烈减低铁的S-K-K内耗(Q^-1)、降低内耗峰温度(T_p)和明显减小其弛豫激活能(H)。在铁中磷的固溶限度以下,内耗峰高度(Q_h^-1)随合金中磷浓度的三分之二次方(即位错线上磷浓度平方)C_p^2/3增加而线性减低。实验结果符合Schoeck理论。本文还讨论了内耗机制,认为它是非螺(包括刃)位错段拖曳Cottrell气团间隙溶质原子移动产生的。位错段运动以弯曲的方式进行。 关键词：     

Study of dielectric properties of composite insulators for use in medium voltage overhead lines

The dielectric properties of composite insulator materials based on silicone are studied as a function of ageing factors (temperature, UV). Our study includes composite insulators used in the Tunisian Electricity and Gas Company STEG networks (medium voltage overhead lines). Macroscopic characterization using conventional normalized test was performed at the Center of Measurement Tests of El Omrane (Tunis). In the other hand, samples taken from treated insulator are investigated by dielectric spectroscopy technique. The measurement was carried out according to the same ageing factors. So the correlation between the results of standardized tests and those obtained by laboratory characterization is possible. The results of our measurements show the existence of significant dielectric losses in the case of samples that have been aged under temperature and UV radiation. We attribute these losses to the rate of added filler during material elaboration. The dielectric losses increase respectively with time and ageing factors. This increase is remarkable at the vicinity of industrial frequencies.     

Optical performance evolutions of reductive glutathione coated CdSe quantum dots in different environments

Optical performances of reductive glutathione coated CdSe quantum dots were studied under different ageing conditions. The enhancements of luminescence were obviously occurred for the samples ageing under illumination. The quantum yield of CdSe was enhanced continuously over 44 days at room temperature, and reached as high as 36.6%. O₂ was proved to make a certain contribute to the enhancement. The evolutions of the systems during the ageing time were deduced according to the variations of pH values with ageing time and the XRD results of the samples ageing in air with illumination. We conferred that the reduction of surface defects resulted from the photo-induced decomposition of CdSe quantum dots was the main reason for the enhancement of fluorescence. The production of CdO as a result of the surface reaction with O₂ made contributions to the enhancement for a certain extent. The curves of quantum yield versus ageing time were fitted with a stretched exponential function. It was found that the course of fluorescence enhancement accorded with the dynamics of system with strongly coupled hierarchical degrees of freedom.     

Computational design of precipitation strengthened austenitic heat-resistant steels

A new genetic alloy design approach based on thermodynamic and kinetic principles is presented to calculate the optimal composition of MX carbonitrides precipitation strengthened austenitic heat-resistant steels. Taking the coarsening of the MX carbonitrides as the process controlling the life time for steels in high temperature use, the high temperature strength is calculated as a function of steel chemistry, service temperature and time. New steel compositions for different service conditions are found yielding optimal combinations of strength and stability of the strengthening precipitation for specific applications such as fire-resistant steels (short-time property guarantee) and creep-resistant steels (long-time property guarantee). Using the same modelling approach, the high temperature strength and lifetime of existing commercial austenitic creep-resistant steels were also calculated and a good qualitative agreement with reported experimental results was obtained. According to the evaluation parameter employed, the newly defined steel compositions may have higher and more stable precipitation strengthening factors than existing high-temperature precipitate-strengthened austenite steels.     

Effect of Added Monosodium Glutamate on Characteristics of Polyamide Dope Solutions

Formic acid (FA) solutions prepared with various concentrations of polyamide 66 (PA 66) and monosodium glutamate (MSG) were evaluated in terms of properties, such as density, viscosity, and cloud point. The influence on density was insignificant, whereas the viscosity was strongly affected by the amount of PA 66 and MSG additive. The solutions were further evaluated by casting them in a flat film form and determining the demixing time in a humid atmosphere. The considered cases at lower polymer concentrations at various MSG amounts, indicated that the demixing time increased with increase in polymer concentration. The time for demixing, however, decreased for a given higher amount of polymer when the amount of additive was increased in the dope solution. Membranes were prepared at various coagulant bath temperatures. The tensile strength and degree of adsorption (DOA) of these membranes were found. The tensile strength was higher when the membranes were prepared at higher temperature. The DOA, on the other hand, was higher for the membranes formed at lower temperature.     

Electrical properties of silver iodide

The electrical conductivity of γ- and β-AgI pellets was measured as a function of temperature over the range between 20 and 145 °C. The electronic contributions to the conductivity were studied by using the polarization cell (?) Ag/sample/graphite(+) in addition to experiments in an iodine atmosphere. The increase in conductivity of β-AgI due to the addition of Pbl₂ was also investigated.     

13C NMR lineshapes of acetone adsorbed on silica

¹³C NMR data, obtained as a function of temperature with magic-angle spinning (MAS) and either cross polarization or direct polarization, are reported on acetone and a sample of acetone (an approximately equal mixture with ¹³C labels at C-1 or C-2) adsorbed on dry silica gel. Various contributions to the observed linewidths and T^C₂ values are considered in terms of a previously established model of the acetone/SiO₂ system; in that model, acetone species are in equilibrium between a physisorbed-acetone (non-hydrogen-bonded) state and a state consisting of acetone units that are hydrogen bonded to silanol moieties on the silica surface. Spin dynamics simulations are useful in interpreting the effects of variations of experimental parameters. It is concluded that the main linewidth contributions, which increase at lower temperatures, are: (a) a dispersion of chemical shifts in the hydrogen-bonded state, associated with the inhomogeneous character of the silica surface; (b) the interference between MAS averaging of the chemical shift anisotropy (especially for the carbonyl carbon) and molecular motion and/or chemical exchange; and (c) chemical exchange broadening. Prominence of the last of these contributions is most consistent with data obtained as a function of magnetic field strength, MAS speed, and temperature.     

Grain refinement and strengthening of a Cu–0.1Cr–0.06Zr alloy subjected to equal channel angular pressing

Abstract

The grain refinement and mechanical properties of a Cu–0.1Cr–0.06Zr alloy subjected to equal channel angular pressing (ECAP) at a temperature of 673 K were examined. The microstructure evolution was characterised by the development of a large number of low-angle subboundaries at small strains. An increase in the true strain resulted in gradual transformation of low-angle subboundaries into high-angle grain boundaries that was assisted by the deformation micro-banding. The development of new ultra-fine grains was considered as a kind of continuous dynamic recrystallization, the kinetics of which was characterised by a sigmoid-type dependence on strain and could be expressed by a modified Johnson–Mehl–Avrami–Kolmogorov equation. ECAP led to significant strengthening of the alloy. The yield strength increased from 105 MPa in the initial state to 390 MPa after 8 ECAP passes. A modified Hall–Petch relationship was applied to analyse the contributions of grain refinement and dislocation density to the overall strengthening. In spite of significant strengthening, the electro-conductivity remained at a level of 80% IACS.     

Damage monitor and life prediction of carbon fiber-reinforced ceramic-matrix composites at room and elevated temperatures using hysteresis dissipated energy-based damage parameter

In this paper, the damage monitor and life prediction of carbon fiber-reinforced ceramic-matrix composites (C/SiC CMCs) have been investigated using the hysteresis dissipated energy-based damage parameter. The evolution of the interface shear stress, hysteresis dissipated energy, hysteresis dissipated energy-based damage parameter and the broken fibers fraction vs. cycle number, the fatigue life S?N curves of unidirectional, cross-ply and 2.5D C/SiC composites at room temperature and 800 °C in air atmosphere have been analyzed. For unidirectional C/SiC, the hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter first increase and then decrease with cycle number, and the fatigue limit stress decreases from 88% tensile strength at room temperature to 20% of the tensile strength at 800 °C in air atmosphere; for cross-ply C/SiC, the hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter decrease with increasing applied cycles, and the fatigue limit stress decreases from 85% tensile strength at room temperature to 22% tensile strength at 800 °C in air; and for 2.5D C/SiC, the hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter increases with cycle number, and the fatigue limit stress decreases from 70% tensile strength at room temperature to 25% tensile strength at 800 °C in air.     

Oxygen-ion conducting electrolyte materials for solid oxide fuel cells

Oxygen-ion conducting solid electrolyte systems have been reviewed with specific emphasis on their use in solid oxide fuel cells. The relationships between phase assemblage, electrolyte stability and ionic conductivity have been discussed. The role of parameters such as sintering temperature and atmosphere which influence the segregation of impurities, present in the starting ceramic powders, at grain boundaries and at the external surface of the electrolyte compacts has been emphasised. The stability of various electrolyte materials in contact with other fuel cell components and in fuel environments has been discussed in detail. The ageing behaviour at fuel cell operating temperatures has been described. Data on ionic conductivity, mechanical and thermal properties have been presented for a number of electrolyte materials.     

Optical transmission loss in tin oxide thin film waveguide

This paper reports the optical transmission loss of tin oxide thin film waveguide. The effect of oxidation temperature, thickness and air ageing (40 days at room temperature) was studied. The vapour chopping technique has been used successfully to reduce the optical transmission loss. The vapour chopped tin oxide thin film waveguide (2.90-3.60 dB/cm) showed smaller transmission loss than those of nonchopped tin oxide thin film waveguide (4.16-4.74 dB/cm). Transmission loss was found to be a function of oxidation temperature and thickness. Due to increased oxidation temperature, transmission loss was found to decrease. The effect of increase in thickness was to increase the transmission loss. The air ageing effect caused the increase in transmission loss whereas the effect was found lesser in the vapour chopped tin oxide thin film waveguide.     

Working fluids for heat transformers

A large amount of thermal energy, in the temperature range of 50–90°C, released to the atmosphere by many commercial installations such as agrofeed, paper mills, dairies and process industries, can be upgraded making possible its use in various forms. Many attempts have benn made in most industrial sectors to recovery this energy by heat pumps, organic Rankine cycles and heat transformers. Among various possibilities, heat transformers present an attractive solution as low level heat can be transformed into a higher temperature with minimum consumption of external energy. Further transformers do not require high maintenance and operating cost.The theoretical performance characteristics of single stage heat transformers using various promising binary mixtures as working fluids have been discussed in this paper. The coefficient of performance, energy efficiencies and mass circulation ratio have been analysed as a function of heat delivery temperature. The comparison of working fluids has also been discussed.