Stages Of Deformation Hardening Research Articles

On the macroscopic phenomena of plastic flow localization and solids microscopic characteristics

In the paper to be submitted the notions of plastic flow localization are outlined. It is shown that a particular kind of localized plasticity pattern corresponds to a given stage of deformation hardening. In the course of plastic flow development a changeover in the types of localization patterns occurs. It is found that the emergent patterns are manifestations of the autowave nature of plastic flow localization process, each pattern corresponding to a definite type of autowave. The most intriguing localization pattern corresponds to a phase autowave which forms at the stage of linear work hardening. The following characteristics of phase autowave have been determined experimentally: propagation velocity and dispersion dependence of wavelength. Moreover, elastic-plastic strain relation is introduced which relates the elastic and plastic properties of the deforming medium. It is shown that the characteristics of autowaves follow from this relation.

Stress-strain dependence and the evolution of dislocation structure in Cu-Mn polycrystalline concentrated solid solutions

Deformation of metallic materials results in dislocations occurrence and accumulation, with establishment of their definite distribution (dislocation substructure). The type of dislocation substructure (DSS) defines largely resistance to deformation and fracture of materials. Quantitatively the interrelation of DSSs and resistance to deformation are studied on a limited number of alloys. Foreign literature lacks studies referring to those issues. The given paper investigates the stress-strain dependences in Cu-Mn polycrystalline solid solutions. Mn concentration in the alloys varied within the range of 10…25 at.%. Polycrystals with 10 and 240 μm mean grain size were investigated. Deformation was applied by means of tension at the velocity of 2.10-2 s-1 and the temperature of 293 K. Using transmission electron microscope at the accelerating voltage of 125 kV, microstructure of the samples was investigated when they were deformed up to various deformation degrees. The types of DSSs were defined. The connection of the deformation stage under tension with the formed types of DSS was discussed. The sequence of transition of DSSs during the process of alloys deformation was defined. Appearance of the new stage of deformation hardening is attributed to the occurrence of the new type of substructure. The occurring “new” DSS develops during the deformation process, while “the old” DSS gradually disappears. Each of the stage of plastic deformation generally has two types of DSSs. The connection of the deformation stage and the strain hardening coefficient with the DSS was defined and it was shown to possess the definite dislocation density.

ИЗУЧЕНИЕ НЕОДНОРОДНОСТИ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ СПЛАВА Д1 МЕТОДОМ КОРЕЛЯЦИИ ЦИФРОВЫХ СПЕКЛ-ИЗОБРАЖЕНИЙ

The paper presents the study of the influence of hydrogen enrichment of D1 aluminum alloy using the electrolytic method on the plastic flow localization. The study was carried out on the aluminum alloy samples before and after hydrogen addition using the three-electrode electrochemical cell. It is determined that hydrogen influences significantly the mechanical properties and plastic flow curves of the material under the study. The analysis of deformation curves staging showed the existence of the following stages of plastic flow: the stage of linear deformation hardening, the stage of parabolic deformation (Tailor) hardening and the stage of pre-destruction. To determine and visualize the zones of localized deformation, the authors used the method of digital speckle images correlation allowing getting the deformation quantitative characteristics, i.e. defining the displacement vector field in flat sample during the tension and then calculating the plastic distortion tensor components (the local stretching e xx , the shift e xy and the turn ω z ). When using this methodology in the process of sample loading, the images of deformation evolution and the character of its localization in a deformable sample at various stages of deformation hardening in the initial state and after hydrogen-saturation during 100 hours were determined. The information on the regularities of distribution of the fronts of plastic deformation localization within the material under the study is important for the detailed study of the process of aluminum alloys plastic flow. The study of this process allows predicting at the early stages the area of deformation neck formation and determining the place of future material destruction. Using the X-ray spectrographic microanalysis, the authors got the information on the existence of hardening intermetallic particles.

Elastoplastic Invariant Relation for Deformation of Alkali-Halide Crystals

Plastic strain localization patterns in compression-strained alkali halide (NaCl, KCl, and LiF) crystals have been studied using a double-exposure speckle photography technique. The main parameters of strain localization autowaves at the linear stages of deformation hardening in alkali halide crystals have been determined. A quantitative relationship between the macroscopic parameters of plastic flow localization and microscopic parameters of strained alkali halide crystals has been established.

On the localization of plastic strain under compression of LiF crystals

The plastic flow localization patterns for alkali halide LiF crystals under compression have been investigated. The main spatiotemporal regularities of the strain localization at different stages of deformation hardening in the single crystals have been established. The relation has been traced between the orientation of localized strain zones and the crystallography of slip systems of the test specimens studied simultaneously by the double-exposure speckle photography and photoelasticity methods.

On the localization of plastic flow under compression of NaCl and KCl crystals

The plastic flow localization patterns for alkali halide crystals under compression are investigated. The main spatiotemporal regularities of the strain localization at the stages of deformation hardening in these single crystals are established. The relation is traced between the orientation of localized strain zones and the crystallography of slip systems of the test specimens at the initial stages of plastic deformation. The velocity of motion of localized strain zones under compression is determined.

On plastic deformation of Pb0·95Sn0·05Se single crystals

Abstract Stress-strain characteristics of Pb0·95Sn0·05Se single crystals grown from the vapour phase have been investigated in the plastic deformation range. Samples were compressed along a (100) direction, with strain rate varying between 1·85 × 10−5 and 1·85 × 10−3 s−1, in the temperature interval 300–573 K. Plastic deformation was found to include all three stages of deformation hardening and to be performed by slip of dislocations on the {110} (110) slip system. In conditions when deformation took place in a single-slip system, internal and effective stress values were determined in the easy-glide region. The stress relaxation method was used, taking into account the hardening in process of relaxation. The effective stress as a function of strain rate was found to obey a power law, while the temperature dependence had a thermally activated character. Values of activation parameters were found as a function of effective stress by thermal activation analysis. The results obtained are interpreted in the paper by a model of dislocation interaction with systems of intrinsic point defects in the lattice.