Stored Energy Measurements Research Articles

Effect of fine second phase particles on stored energy and recrystallization kinetics of cold rolled copper single crystals

<mml:math><mml:mrow><mml:mo>(</mml:mo><mml:mn>111</mml:mn><mml:mo>)</mml:mo><mml:mo>[</mml:mo><mml:mn>1</mml:mn><mml:mover><mml:mn>1</mml:mn><mml:mi>¯</mml:mi></mml:mover><mml:mn>0</mml:mn><mml:mo>]</mml:mo></mml:mrow></mml:math> crystals of pure Cu–Al203 (particle size < 200 nm) have been strained between 5 and 204% by rolling. Stored energy measurements have been made by differential scanning calorimetry, and the recrystallization kinetics established. The stored energy of cold work is found to increase linearly with prior strain up to a saturation value. The presence of the second phase raises the stored energy by an amount proportional to the volume fraction of particles and also to the magnitude of the applied strain. Internal oxidation of pure Cu leads to the acceleration of recrystallization. Cu–Al203 crystals exhibit a change from suppressed to retarded to accelerated recrystallization as the strain is increased. To explain this a model based on nucleation at microbands is proposed.

Measurement of the stored energy of copper single crystals by means of a new deformation calorimetry method

A new method of deformation calorimetry was employed for the measurement of stored energy of a Cu crystal oriented for single glide and a crystal with [100] axis. Bar-shaped specimens were deformed in tension with constant deformation rate at room temperature. The evaluation of measured temperature curves, the main difficulty of deformation calorimetry, is performed by means of an experimentally recorded response function. Any temperature change of the specimen can be represented mathematically in terms of this response function and subsequently be evaluated numerically. The physical differences between the stored energies measured by annealing and deformation calorimetry, the question of the most convenient thermodynamic definition of stored energy and the change of enthalpy resulting from a change of specific heat due to plastic deformation are treated. The dependence of stored energy and its change with deformation on crystal orientation and deformation extent are discussed. A quadratic dependence of stored energy on shear stress, predicted theoretically, applies for Cu crystals deformed at room temperature only for small degrees of deformation; for higher ones a cubic dependence is approached.

Measurement of stored energy of KBr after X-irradiation at low temperature

The release of stored energy of X-irradiated KBr measured between 10 and 50K. A very sensitive heat flow calorimeter is described, which allows the detection of energy release rates as small as 0.5% of the heat capacity of the sample. The observed annealing stages of stored energy are compared with lattice parameter, length change, and optical absorption measurements from similar annealing experiments. The energy release can be identified as due to recombination of Frenkel pairs. The stored energy per Frenkel pair was obtained in KBr by combined measurements of the energy release and the change of optical absorption while warming up an irradiated crystal. For the alpha +I Frenkel pair a value of (4.0+or-0.8) eV was found. For the recombination of an F+H Frenkel pair an energy release of (2.7+or-0.6) eV was obtained.

Measurement of stored energy of KCl after 4·6°K reactor irradiation

Five KCl single crystals were irradiated at 4·6°K in the core of the Munich Nuclear Reactor for periods of 100 sec, 10 min, 1 hr or 10 hr, respectively. After irradiation the stored energy of the samples was measured in a differential-heat-flow calorimeter at two different heating rates: 0·29 and 1·1°K/min. At 0·29°K/min peaks of stored energy release were resolved at 21°K, near 27·5°K, at 32·5°K, at 42·5°K and near 50°K. An attempt was made to evaluate the corresponding activation energies using two different methods (see Table 1 in the text). The annealing stages at 21 and 32·5°K correspond to first order kinetics. The annealing stages at 42·5 and near 50°K are not of first order. A similar experiment was performed on KBr single crystals and is reported in the preceding paper. The results are compared with annealing studies on low temperature X-irradiated KCl and KBr crystals. From both our experiments it follows that also during reactor irradiation at 4·6°K ionization mechanisms of defect production should be responsible for the four observed low temperature recovery peaks; only defect recovery at higher temperatures may be at least partially explained by recombination of collision produced defects, i.e. the typical neutron irradiation effect as it takes place in metals.

Measurement of stored energy of KBr after 4·6°K reactor irradiation

Four KBr single crystals were irradiated at 4·6°K in the core of the Munich Nuclear Reactor for periods of 100 sec, 10 min or 1 hr, respectively. After irradiation the stored energy of the samples was measured in a differential-heat-flow calorimeter at heating rates of 0·29°K/min and 1·1°K/min. At 0·29°K/min peaks of stored energy release were resolved near 11 and 20°K and at 25, 38 and 45°K. An attempt was made to evaluate the corresponding activation energies using two different methods (see Table 1 in the text). The 25°K annealing stage is due to a first order recombination reaction. The anneling states near 20, at 38 and at 45°K do not correspond to first order reactions. Our results are compared with annealing studies on low temperature X-irradiated KBr crystals. A similar experiment was performed on KCl single crystals and is reported, together with a more detailed comparison and discussion of both experiments, in a later paper[14].

Stored energy measurements in copper single crystals tensile deformed at 20°C

Copper single crystals (99.999 per cent purity) of orientations near 〈110〉, 〈111〉, 〈311〉 and 〈322〉 have been tensile deformed at room temperature to different shear stresses within stage III. The energy stored in these crystals has been measured by heating them within an adiabatic twin calorimeter of high precision to temperatures above recrystallization. No stored energy release was observed below the recrystallization temperature. The stored energies measured during recrysatllization temperature. The stored energies measured during recrystallization were smaller by a factor of two or more than comparable data obtained by deformation calorimetry. The stored energy increased with the square of the shear stress for crystals deformed up to shear stresses of about 8 kp/mm 2. The ratio of stored energy to expended work amounted to about 6 per cent.

Relationship in polypropylene melt between its linear viscoelasticity and its steady capillary flow properties

AbstractIt is the object of the present study to obtain clear knowledge of the relations in the polypropylene melt between its linear viscoelasticity and its nonlinear steady capillary flow, paying particular attention to the elastic properties in its capillary flow. By representing the linear viscoelasticity numerically with zero‐shear viscosity, η0, and steady‐state compliance, J, evaluation has been made of the properties concerning the elasticity of polymer melt in the capillary flow, such as non‐Newtonianity, the entrance pressure loss, the end correction, the Barus effect, and the melt fracture. The steady flow viscosity η, the entrance pressure loss P0, the critical shear stress, τc, and the critical shear rate $\dot \gamma _c$ at which melt fracture begins to occur are subject to η0 as follows: From the well‐known relationship between η and the weight‐average molecular weight M̄w, these quantities are governed by M̄w. Meanwhile, for such quantities as structural viscosity index N, end correction coefficient ν, and elastic pressure loss ratio P0/P, following correlations hold: As η0 and J are respectively determined mainly by M̄w and the molecular weight distribution MWD, these quantities are governed by both M̄w and MWD. Physical meanings of η0·J and η02 · J are, respectively, mean relaxation time and a measure of stored energy in steady flow. The Barus effect has a positive correlation to J, ν, and P0/P. (The symbol ∝ employed here means positive correlation.)

The Relationship in the Polypropylene Melt between its Linear Viscoelasticity and its Steady Capillary Flow Properties

It is the object of the present study to obtain clear knowledge of the relations in the polypropylene melt between its linear viscoelasticity and its non-linear steady capillary flow, paying particular attention to the elastic properties in its capillary flowBy representing the linear viscoelasticity numerically with zero-shear viscosity, ηo, and steady-state compliance, Je0, evaluation has been made of the properties concerning the elasticity of polymer in the capillary flow, such as non-Newtonianity, the entrance pressure loss, the end correction, the Barus effect and the melt fracture.The steady flow viscosity, η, the entrance pressure loss, Po, the critical shear stress, τc, and the critical shear rate, γc, at which melt fracture begins to occur, are subject to ηo as follows:logη∝logηo, logPo∝logηo, τc∝-logηo, logγc∝-logηo.From the well-known relationship between ηo and the average molecular weight, Mw, these quantities are governed by Mw.Meanwhile, for such quantities as structural viscosity index, N, end correction coefficient, ν, and elastic pressure loss ratio, Po/P, following correlations hold: N∝log(ηo, Je0), logν∝log (ηo2·Je0), Po/P∝log(ηo2·Je0).As ηo and Je0 are respectively determined mainly by Mw and the molecular weight distribution, M.W.D., these quantities are governed by both Mw and M.W.D.Physical meanings of ηo·Je0 and ηo2·Je0 are respectively mean relaxation time and a measure of stored energy in steady flow. Barus effect has positive correlation to Je0, ν and Po/PThe symbol employed here, ∝, means the positive correlation.

Thermal annealing of irradiated lithium hydride—. Measurement of stored energy

The release of stored energy from irradiated LiH during thermal annealing was measured with a differential thermal analysis technique. For all samples irradiated with 60Co γ-rays to doses between 1 × 10 9 and 5 × 10 10 rad. at temperatures ranging from 40 to 270°C, the amount of stored energy was directly proportional to the amount of ‘motionally narrowed’ hydrogen seen in the material by pulsed nuclear magnetic resonance. The energy release is from the recombination reaction of free lithium and hydrogen that have been produced by irradiation; the energy for the reaction Li (c)+ 1 2 H 2(c) → LiH(c) was ∼20kcal/mole. This is comparable to the standard heat of formation of LiH, ΔH° ƒ = −21·7 kcal/mole .

Thermal annealing of irradiated lithium hydride I. Measurement of stored energy

Thermal annealing of irradiated lithium hydride I. Measurement of stored energy

Calorimeter for Simultaneous Measurements of Stored Energy and Resistance

An adiabatic calorimeter using digital data acquisition and programmed heating for measurement of stored energy in the range 350–1000 K is described. In addition to combining the advantages inherent in digital acquisition systems with the advantages of an adiabatic calorimeter, samples were heated by Joule heating permitting (1) simultaneous measurement of stored energy and resistance and (2) calibration of the system including losses. This arrangement, when applied to measure the stored energy and resistance associated with defects introduced in samples by quenching, plastic deformation, or radiation damage, has sufficient sensitivity not only to measure the total stored energy but also to yield a spectrum of the energy release as a function of temperature. Calibration data indicated that energy release rates as small as 10 μW could be measured. Measured losses which were nearly independent of temperature totaled approximately 5.5 μW. Resistance measurements were reproducible to better than 10 parts in 10.6

Etude des defauts crees dans le beryllium par irradiation a basse temperature

Beryllium samples (impurity content 0.1%) were irradiated by neutrons at 27 °K and 77°K and by electrons at 20 °K. Defect production and subsequent recovery were studied essentially by means of electrical resistivity and stored energy measurements. The defect concentration increases with increasing flux and energy of the particles. After room temperature annealing more than 95% of the initial radiationinduced resistivity increment is recovered. Three principal recovery ranges were observed: stage I below 80 °K, stage II between 95 and 220 °K, and stage III between 220 and 300 °K. Each of these stages presents substructure, the dose-dependence of which was also studied. The experimental data are discussed in terms of published models for other metals.

The relation between physical properties and the observed dislocation distribution in fatigued metals

Recent experiments have suggested that the dislocation distribution observed by transmission electron microscopy of deformed metals may not be wholly representative of that in the bulk metal. Direct observation of the dislocation configuration in polycrystalline copper after unidirectional and reverse straining, in combination with measurements of stored energy and macroscopic density, suggest that the thin foils in this case, are at best representative of recovered bulk specimens. For specimens of α-brass fatigued at low stress no dislocation loops are observed in thin foils, in contrast to previous observations on Al, Cu, Au and Ni. These results, taken together with previous observations on the annealing of fatigue hardening, can only be explained satisfactorily by assuming that it is in fact true that thin foils are not always wholly representative of the bulk. A qualitative model of the dislocation arrangement in fatigued f.c.c. metals is proposed which is in accord with the experimental observations.

Electrical resistivity of dislocations in face-centred cubic metals

Abstract Measurements of stored energy, electrical resistivity, density and hardness on gold and silver deformed 75% in compression are presented, and compared with previous results for copper. It is shown that the resistivity of a dislocation calculated from the experimental results differs very little in copper, silver and gold, although their stacking-fault energies are now considered to differ widely. This suggests that stacking faults do not make an important contribution to the resistivity of deformed metals.

Dislocation patterns in graphite

A detailed analysis is given of the dislocation patterns observed by means of electron microscopy in graphite single crystal flakes. It is found that the dislocations are ribbons consisting of two partiale of the Shockley type separated by a strip of stacking fault. All patterns can be interpreted in a consistent way on the basis of this model and on the assumption that only small energy stacking faults occur, i.e. faults consisting of a lamella of rhombohedrally stacked material. The stacking fault energy is obtained from the width of the dislocation ribbons and from the shape of extended nodes of partials with known Burgers vector. The dependence of the width of the ribbon on the angle between the direction of the ribbon and the Burgers vector is checked, and it is shown that this can be used to determine an effective Poisson's ratio. The possible interactions between ribbons are discussed from a theoretical point of view and compared with observed configurations. The Burgers vectors were determined experimentally by making use of contrast effects. Graphite quenched from 3000° C and annealed at 1200° C is found to contain vacancy loops. The annealing peak at 1200–1300° C, found previously by means of electrical measurements and measurements of stored energy, is therefore associated with the formation of vacancy loops. It is shown that from a determination of the Burgers vector a conclusion as to the nature of the loops can be reached. The interaction between vacancy loops and glissile dislocations is discussed from a theoretical point of view. It is shown that vacancy loops tend to form preferentially in the stacking fault ribbons. The formation mechanism and the structure of dislocation networks are discussed as well as the nature of the twin boundaries. Dislocation movement and the formation of constrictions in the ribbons are discussed.

The influence of impurities on the annealing of nickel after cold work

Measurements of stored energy and of changes in electrical resistivity and density accompanying annealing have been made on nickel of 99.85 per cent purity deformed in torsion and compression. There are notable differences from the behaviour found previously for nickel 99.6 per cent purity. The results suggest that, in the purer nickel, little or no recovery involving dislocations occurs between room temperature and the recrystallization temperature, in contrast to previous results for 99.6 per cent pure nickel. There appear to be two stages of annealing prior to recrystallization in the 99.85 per cent material although they are not clearly resolved. These are centred at 120°C and 260°C and are tentatively ascribed to the annealing of interstitials and vacancies respectively. On this basis the observed changes in resistivity and density can be explained. Stored energy measurements on still purer nickel specimens, 99.96 per cent, deformed in compression indicate that in this material these first two stages are clearly resolved, provided the deformation is low enough to ensure that recrystallization does not interfere with their observation.

Observations of the Emission of Light on Dissolution of Irradiated Solids in Certain Liquids

Ahnstrom and Ehrenstein have observed the emission of light on dissolution of some organic solids in water1. We have been concerned with measurements of stored radiomimetic energy in solids treated with ionizing radiation. This problem has been approached partly by dissolution in liquids typical for dosimetry by the methods of radiation chemistry and partly by attempts to excite, during dissolution, liquid scintillators2. Some results of the latter kind will be summarized here. Most of the experiments were concerned with fine-grained sodium chloride which was given doses up to 200 Mrads of cobalt-60 γ-radiation and 2-MeV. electrons from a Van de Graaff machine.

Strain-broadening of nuclear magnetic resonance lines in copper

Abstract The mean-square width of the nuclear magnetic resonance absorption line in copper sheet has been measured with an accuracy of ± 4%, using specimens from a sample of copper (99–98% Cu) on which stored energy measurements had already been made (Clarebrough et al. 1957). Plastic deformation has been found to increase the mean-square line width by up to 40% and there is evidence that the bioadening is proportional to the stored energy. There is also a small reduction in the integrated intensity of the line in deformed specimens, possibly caused by the high strains in regions near the cores of dislocations. The results can be interpreted satisfactorily on a model where both the line width and the stored energy are calculated from the state of strain of the material.

The dislocation distribution, flow stress, and stored energy in cold-worked polycrystalline silver

Abstract Distribution and densities of dislocations, determined by electron transmission microscopy, flow stress and stored energy measurements (by microcalorimetry) on cold-worked polycrystalline silver are correlated with each other, The dislocations are arranged in dense networks forming the boundaries of an otherwise relatively dislocation-free cell structure. The flow stress is explained quantitatively in terms of the forest intersection mechanism at the boundaries. The stored energy after recovery is of the same order as the total self-energy of the dislocation arrangement, so that the long-range stresses must be largely relaxed. The considerable energy release during the recovery stage produces no observable change in dislocation distribution. This recovery stage is thought to be due to the relief of long-range stresses or to the removal of point defects. While the values of flow stress and stored energy can be accounted for in terms of the observed non-uniform distribution of dislocations (cell structure), they are not compatible with each other on a model based on a uniform distribution of pile-ups; nor are pile-ups observed on the electron micrographs.

Investigation of the annealing of nickel deformed by compression by X-ray and stored energy measurements

Abstract X-ray diffraction patterns from bulk specimens of nickel deformed by compression have been measured with a Geiger-counter spectrometer. A composite specimen has been used to overcome the effects of preferred orientations. The results indicate that during the annealing there is no change in the background intensity. No evidence has been found for stacking faults or changes in lattice parameter. The integrated intensities of all lines remain constant up to a temperature of annealing of about 480[ddot]c. A large decrease (30–75%) in the integrated intensity of all lines occurs on annealing to 600[ddot]c and this is attributed to extinction; an estimate of 2–4 μ is obtained for the size of the 'perfect' regions required to produce this effect. The diffraction profiles are analysed by a number of methods. The broadening produced by the particle size effect is small. The stored energies derived from the various methods of analysis range from 0.04-2-4cal/g. Best agreement is obtained between values of s...