Reduction Of Stored Energy Research Articles

Formation of η-oriented shear bands and its significant impact on recrystallization texture in strip-cast electrical steel

The evolution of shear band (SB) and texture in strip-cast electrical steel was studied in order to investigate the crystallographic character of SB and its influence on recrystallization texture. Shear deformation in the form of SB played an effective role in tailoring the local lattice rotation to accommodate heavy deformation in the case of inhomogeneous deformation under conditions of initial coarse grain in strip-cast electrical steel. During rolling process, η-oriented SBs appeared at different stages of deformation as a result of geometric softening. Cube-oriented SB was mainly retained from initial exact Cube grain at early stage of shear deformation and Goss-oriented SB was newly developed during the formation of γ-fiber matrix after heavy deformation. {210}<001> SB formed as a transition form among different SBs. Crystal rotation inside SB, SB dimension and SB boundary misorientation progressed in proportion to cold rolling reduction. It is demonstrated that crystallographic direction of SBs tended to be parallel to <001> under the driving force of reduction in stored energy to maintain relatively quasi-stable state. Low orientation gradient as well as relatively low density of dislocations was developed within SB region, while high orientation gradient formed between SB region and surrounding matrix. Interestingly, the η-oriented cell blocks inside SBs provided preferential nucleation sites for Goss and Cube texture at early stage of recrystallization, which significantly contributed to beneficial recrystallization texture in a manner of texture inheritance and superior magnetic properties (B50 was as high as 1.81 T, and P1.5/50 was as low as 4.0 W/kg).

Misorientation dependence of the grain boundary migration rate: role of elastic anisotropy

ABSTRACT In this work, numerical computations of image forces and stored energy during the growth of a strain free grain within a recovered matrix containing an array of identical dislocations are performed. A decrease of the stored energy is observed when image forces are attractive and an increase when image forces are repulsive. The variation of elastic energy depends closely on the material elastic anisotropy, the number of dislocations in the array and its initial distance to grain boundary. For an array of 20 edge dislocations and the motion of a planar grain boundary over approximately 180 atomic spacing, the magnitude of the energy variation is on the order of one dislocation line energy for Al and six for Cu, which is significant in both cases. Furthermore, by sweeping the whole orientation space for FCC crystals, it is shown that grain boundaries near a misorientation are among those that can display the highest attractive forces on edge dislocations. Since grain boundary migration is driven by the reduction of stored energy, the results are analysed in light of experimental recrystallization data in FCC metals which show that the fastest moving boundaries are often characterised by misorientation axis around and misorientation angle close to .

Effect of fin material on PCM melting in a rectangular enclosure

A comprehensive study was conducted to analyse the effect of fin material on PCM melting in a rectangular enclosure. Four commonly employed indicators, surface averaged Nusselt number, melting time, total stored energy and mean power, and two proposed, stored energy per mass and cost per energy stored, were used to evaluate the influence of fin material roundly. Results show that compared with the no-fin scheme, the PCM melts faster and the melting time is reduced by 41.6%, 41.0%, 40.1% and 37.2% with inserting copper, aluminum, carbon steel and steel302 fins. Significant reduction in stored energy per mass is presented by adding fins and the decline range is the highest for the copper fin scheme and the lowest for the aluminum fin scheme, which is 27% and 9.4% respectively. Among four fin schemes, the cost per energy stored is the largest for the copper, 5.6% higher than the no-fin case. The selection of fin material is affected by adopted indicators. If four commonly used indicators are considered only, the copper and carbon steel fin schemes are highly recommended, while the aluminum fin scheme is highly recommended if six indicators are considered simultaneously. A criterion, selecting fin material with higher thermal conductivity, high specific heat capacity, low density and low cost as fins, is proposed.

Study of static recrystallization behavior in hot deformed Ni-based superalloy using cellular automaton model

A cellular automaton model (CA) with probabilistic state switches is developed to simulate the microstructural evolution in a Ni-based superalloy during static recrystallization (SRX). The kinetics of SRX is formulated on a mesoscale level. SRX nuclei grow under the driving pressure resulting from the reduction of stored energy and grain boundary energy. It is found that SRX grain size can be well predicted by the developed CA model. Solute elements of the studied superalloy have a drag effects on grain boundary motion. But, this solute drag effect is not obvious at high deformation temperatures. Nucleation rate of the SRX grain increases with the increase of strain, strain rate, and deformation temperature. Besides, the inhomogeneity of grain size first increases, then decreases with the increase of SRX fraction. The changes of inhomogeneity mainly result from the evolutions of the primary and SRX grain sizes.

Characterization of Si particles and their effects on and recrystallization in a nanostructured cold rolled Al-1% Si alloy

An Al-1.08 vol.% Si alloy was cold rolled to a reduction of 98% (εvM = 4.5) and then annealed at different temperatures up to 210°C (0.52 Tm) for different times. The deformed structure is characterized by a nanoscale lamellar structure with the presence of Si particles of coarse (> 1 μm), medium (100 nm - 1 μm) and fine (< 100 nm) sizes in the microstructure. Deformation zones are formed around the coarse Si particles and the boundary spacing is finer in the deformation zone than in the matrix. The medium Si particles have little effect on the morphology and boundary spacing. The fine Si particles are aligned along the lamellar boundaries indicating a stabilizing effect on the structural refinement during cold rolling. After annealing, enhanced recovery occurs in the deformation zones around the coarse Si particles. However the reduction in stored energy during recovery and the pinning effect of fine Si particles on the boundary migration prevent the advantage of particle stimulated nucleation (PSN) of coarse Si particles in the nanoscale lamellar structure. This study also demonstrates an important effect of the fine particles in delaying both recovery and recrystallization processes. This effect diminishes with increasing annealing temperature and coarsening the fine particles especially at triple junctions.

Significant reduction in volume, stored energy and magnetization loss of high-field magnet coil based on the improvement of critical current characteristics in GdBCO coated conductor

We have characterized current transport properties in a GdBa 2Cu 3O 7−δ coated conductor fabricated by a combination of ion-beam assisted deposition (IBAD) method and pulsed laser deposition (PLD) method with reel-to-reel systems, and have applied them to a coil design for a high-field magnet. The J- E characteristics in the conductor are given as a function of temperature, magnetic field and the field angle based on percolation transition model, and its potential as a high-field magnet coil is discussed based on a finite element method analysis. As a result, we have found that the conductor with I c = 350 A/cm-w at 77 K and self-field has a possibility to realize a 40 T magnet coil with very compact size (300 mm in outside diameter) and small usage of the coated conductor (8 km). Furthermore, we have also investigated the relationship between the scale of the magnet coil and the corresponding requirements for the conductor. Consequently, it has been suggested that the improvement of critical current characteristics of the conductor greatly advances the downsizing of the coil without large increment in hoop tensile force. In addition, it has also been found that such downsizing of the coil contributes to the reduction in stored energy and total magnetization loss of the coil. This means that the recent improvement of critical current characteristics in coated conductors is especially worthwhile for high-field magnet coils in terms not only of downsizing but also of quench protection and magnetizing/demagnetizing operation.

Computer Model of Recrystallization Texture in Aluminum Alloys

During recrystallization, frequency of occurrence of nuclei with certain orientation depends on the location of the nucleation site, the energy stored at that location and the rate of release of stored energy. A computer model of nucleation of recrystallization process in cold rolled aluminum is developed based on the analysis of misorientation distributions around the nuclei of different orientations and the measured orientation dependent elastic energy stored in the specimen. Comparison of selected locations of nucleation sites with experiment shows that Cube nuclei are located much more randomly in the cold rolled matrix than the rolling texture components, namely, copper, brass, and sulfur. A specific range of rate of release of stored energy increases the frequency of occurrence of the Cube nuclei. Information on the stored energy after cold deformation and stress relieving provides a great deal of understanding on the mechanism that controls the primary recrystallization in deformed metals. From the diffraction peaks that are measured using X-rays in 88% cold-rolled and stress-relieved can body aluminum alloy, stored energy as a function of crystal orientation is calculated. The rate of reduction of stored energy plays a major role in deciding the rate of nucleation of new grains with different orientations. The stored energy of deformation and unique misorientation distribution that cube grains have in the cold rolled matrix is responsible for the enhanced growth rate of the nucleated cube grains. The simulated results are compared with the experimental data. Agreement of these results suggests that in the development of the cube texture, both oriented nucleation and oriented growth play an important role. Software was developed to simulate texture and microstructure transformation during the annealing process.

Effects of Electric Field Annealing on Recrystallization Texture and Plastic Strain Ratio (r-Value) of IF Steel Sheet

Effects of electric field annealing on recrystallization texture and average plastic strain ratio (r value) of IF steel sheet were studied by mean of X ray diffraction ODF analysis and the tensile test. Specimens of 75% cold-rolled IF steel sheet were annealed at 850flC for 25min,with and without electric field annealing respectively. Results show that the electric field annealing does not change the type of recrystallization texture and its formation mechanism in IF deep-drawing steel sheet, but improves the formation and development of recrystallization i-fiber texture, enhances the intensity of i-fiber texture, and retards the formation and development of c-fiber texture. Comparing with the conventional annealing, electric field annealing improves the average plastic strain ratio (r value). Possible reasons for the intensification of recrystallization i-fiber texture with the electric field applied may attribute to the reduction of stored energy, thus hindering the formation of other orientated nuclei and enhancing the nucleating ratio of i-oriented nuclei. And the intensification of recrystallization i-fiber texture was considered as the main reason for the enhancement of the plastic strain ratio (r value) in IF steel sheet.

Stored energy in can body aluminium alloy after cold rolling and stress relieving

Information on the stored energy after cold deformation and stress relieving would provide a greater understanding of the mechanism that controls the primary recrystallisation in deformed metals. Stored energy as a function of crystal orientation of 88% cold rolled and stress relieved can body aluminium alloy is calculated using the diffraction peaks from X-ray analysis. The obtained stored energy values are presented in the form of a stored energy distribution function on Euler angle space similar to the orientation distribution function. The stored energy along the β fibre that characterises the deformation texture and cube recrystallisation texture components is discussed in detail. A significant reduction of stored energy for the cube texture component after stress relieving is observed.

Clinical experience with downsized lower energy output implantable cardioverter defibrillators

Background and study objective: Technical improvements in cardioverter defibrillators technology has resulted in decrease in can size coupled with improved electrodes technology. A decrease in maximum energy output allows further decrease in device size. The aim of this study was to evaluate the feasibility of a single lead transvenous implant employing a downsized cardioverter-defibrillator (volume 59 cm 3), with a related decrease in maximum energy output (29–31 joules as stored energy and 25–27 joules as delivered energy). Methods and results: Fifty-five patients with ventricular tachyarrhythmias were enrolled in 17 European institutions for implantation. At implantation step-down defibrillation threshold (DFT) was determined and the device was implanted only if a safety margin ≥10 joules was maintained between DFT and maximum programmable output. Implantation was performed in 54 of the 55 referred patients (98%) in a single electrode-device configuration. Step-down DFT testing was performed in 44 patients (43 finally implanted) and DFT was 7.77±4.41 joules (range 3–20). In 20 of the tested patients (45%) DFT was ≤5 joules, in 26 patients (59%) was ≤8 joules and in 34 patients (77%) it was ≤10 joules. No differences were found in DFT comparing patients with left ventricular ejection fraction ≤ or >40% or patients treated or not with antiarrhythmic drugs or β-blockers. Mean implant duration was 85±34 min. Conclusions: Employing a downsized cardioverter defibrillator, successful transvenous implantation can be achieved in 98% of the patients, with maintenance of adequate defibrillation safety margins despite a reduction in stored energy to 29 joules. Implantation of the device with a lead-alone configuration allows short implant times and few perioperative complications.

Reduction of stored energy in a heavily irradiated ceramic

The decrease of stored energy that accompanies redamage of a metamict ceramic is compared with the calculated elastic strain energy resulting from the volume misfit between the disordered inclusions and the crystalline matrix. In the case of self-damaged CaPuTi2O7 it is found that the elastic energy contributes no more than 20% to the observed energy decrease. The major part of this decrease must be attributed to rearrangement of atoms by the redamage process into configurations of lower energy.