Initial Stages Of Plastic Flow Research Articles

TEMPERATURE DEPENDENCE OF THE DEFORMATION BEHAVIOR OF HIGH-ENTROPY ALLOYS CO20CR20FE20MN20NI20, CO19CR20FE20MN20NI20С1 AND CO17CR20FE20MN20NI20С3. MECHANICAL PROPERTIES AND TEMPERATURE DEPENDENCE OF YIELD STRENGTH

This paper discusses the temperature dependence of the mechanical properties of multicomponent alloys Co20Cr20Fe20Mn20Ni20 (Cantor alloy), Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 under uniaxial static tension in the temperature range from 77 to 473 K. It is shown that after thermomechanical treatment all the alloys have an fcc crystal structure, but unlike single-phase Co20Cr20Fe20Mn20Ni20 and Co19Cr20Fe20Mn20Ni20С1 alloys, the alloy with 3 at % carbon exhibits large incoherent chromium carbides. Alloying with carbon causes solid solution strengthening of the austenitic phase and dispersion hardening, and promotes grain refinement in the Cantor alloy. Solid solution strengthening contributes to an increase in the athermal and thermal stress components of σ0.2, leading to higher yield stress values and stronger temperature dependences σ0.2( T ) in Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 alloys than in the Cantor alloy. The results of X-ray diffraction and microscopic analysis indicate that despite the differences in the total concentration of interstitial atoms in Co19Cr20Fe20Mn20Ni20С1 and Co17Cr20Fe20Mn20Ni20С3 alloys, the concentrations of carbon dissolved in the crystal lattice of the austenite phase are close. However, the higher strength properties of Co17Cr20Fe20Mn20Ni20С3 compared to Co19Cr20Fe20Mn20Ni20С1 are determined primarily by grain boundary strengthening and, to a lesser extent, by dispersion hardening. Both factors such as lowering the deformation temperature and alloying with carbon contribute to an increase in the deforming stresses of the Cantor alloy. It is shown that alloying with carbon affects the staged plastic flow of the Cantor alloy: the tensile curves of Co19Cr20Fe20Mn20Ni20С1 carbon alloy exhibit a well-defined stage of microplastic deformation, and the flow curves of Co17Cr20Fe20Mn20Ni20С3 alloy at the initial stages of plastic flow have a parabolic shape, typical of the deformation of alloys with large incoherent particles. The elongation to failure of Co20Cr20Fe20Mn20Ni20 and Co19Cr20Fe20Mn20Ni20С1 alloys increases linearly with decreasing deformation temperature, i.e., the mechanical properties of single-phase alloys are improved in the region of low test temperatures. For Co17Cr20Fe20Mn20Ni20С3 alloy, an increase in strength properties during low-temperature deformation is accompanied by a decrease in ductile characteristics, and the alloy becomes brittle from the viewpoint of macromechanical behavior.

Localized deformation at initial stages of plastic flow in high-manganese steel

The work is devoted to the study of macroscopic localization of plastic deformation during uniaxial tension of single crystals of the Hadfield steel (Fe – 13 % Mn – 1.03 % C). In the course of studies at the stage of easy sliding, significant differences were found in the nature of macrolocalization of plastic deformation in the single-crystal samples under study. All patterns of deformation localization observed in these cases can be divided into two types. The first type of strain localization corresponds to the initiation at the upper yield point and further propagation of the strain front, which gradually transfers the sample material from undeformed state to deformed one. This manifested itself most clearly in single crystals oriented along the tension axis [377] and [355], where the strain localization pattern appears as a single zone of localized deformation on the yield plateau. Such a deformation front passes through the sample volume only once as a Chernov-Luders band. In this case, the flow of the material is carried out without hardening until all its elements are transferred to the deformed state. Single zones of strain localization were also observed at the stages of easy sliding and yield plateau in the Hadfield steel single crystals oriented along the tension axis [123] and [012]. In the second type of localization, at the stage of easy sliding, synchronous movement along the pattern of several deformation centers occurs. Their movement can be unidirectional and counter, and the speeds are both the same and different from each other. Further deformation of the Hadfield steel single crystals oriented along the tension axis [355] or [012], led to the movement of two deformation localization centers at the stages of easy sliding. In single crystals oriented along [111], the strain localization pattern is respectively represented as four localized strain sites. Consequently, the synchronous movement of deformation fronts occurs along an already deformed, albeit to a small extent, material. As a reason for the difference between the two types of macrostrain localization at stage I (the easy sliding stage and the yield plateau), the number of active sliding systems or tensile twinning in the studied single crystals can be discussed based on crystallographic analysis and metallographic studies.

Slip activity in molybdenum single crystals compressed at 77 K

ABSTRACTHigh-purity single crystals of molybdenum of five different orientations were compressed at 77 K to plastic strains between 3% and 4% to investigate the initial stage of plastic flow in these metals. Electron back-scatter diffraction was used to determine the sample orientations before and after deformation to quantify the magnitude and direction of lattice rotation. The slip trace analysis on two perpendicular faces of each prismatic specimen, made using the Nomarski interference contrast, reveals that the slip morphology depends strongly on the orientation of the applied load. The sample oriented near the axis and that of the centre-triangle orientation exhibited sharp slip traces on and planes, whereas the samples oriented near the edge of the triangle yielded by macroscopic slip on a series of high-index planes. The orientations of observed slip traces were compared with theoretical predictions of slip activity of the twelve slip systems made by the Schmid law and using the effective yield criterion developed previously using molecular statics simulations of an isolated screw dislocation under stress.

Evolution of dislocation boundaries during cold deformation of microcrystalline titanium

The evolution of the misorientation spectrum of titanium during cold deformation via uniaxial tension was analyzed. The initial stage of plastic flow (true strain e ∼ 0.1) is characterized by the intense formation of low-angle boundaries (LABs). The axes of rotation of most LABs are close to 〈001〉. This fact can be treated as a consequence of predominant prismatic slip during plastic deformation of titanium. An increase in strain to e ∼ 0.5 and ∼ 1.0 is accompanied by both a gradual increase in the mean misorientation angle of LABs and an increase in the fraction of high-angle boundaries (HABs). Twinning occurs over the entire deformation range under study: twinning on the {112}〈\(\overline 1 \overline 1 \)3〉 system is predominant at the initial stage, and twinning on the {102}〈\(\overline 2 \overline 1 \)3〉 system is predominant at the final stage. It is found that the misorientation spectrum of HABs forming during deformation is dominated by 15°, 30°, and 90° boundaries.

Observation of twin boundary migration in copper during deformation

A previous investigation produced evidence that twin boundaries in annealed copper were a significant source of dislocations during the initial stages of plastic flow. The character of the dislocation source was unknown, but it was hypothesized that twin boundaries could be non-regenerative dislocation sources that would cause migration of the boundary during plastic deformation. Channel die deformation and intermittent orientation imaging were performed on split specimens of pure copper in an attempt to observe twin boundary migration. Approximately 15% of the twin boundaries were observed to migrate beyond that expected from the imposed strain. The data support the hypothesis that twin boundaries can serve as dislocation sources.

Localized strain autowaves at the initial stage of plastic flow in single crystals

Plastic strain localization in single crystals of pure metals and alloys is studied on the yield plateau and at the easy glide stage with a zero or small strain hardening coefficient. The difference between localization patterns in the two cases is explained, and strain localization mechanisms are suggested. At these stages of plastic deformation, various types of autowaves are observed.

Simulation of Frank-Read sources in silicon

A simulation of dislocation sources in silicon is presented which has been developed in order to further examine how dislocation dynamics and multiplication govern the initial stage of plastic flow in diamond cubic crystals. The numerical method is adapted from an existing code by introducing specific dislocation properties deriving from the presence of strong Peierls forces. Most of the results obtained can be qualitatively interpreted in terms of the various contributions to the effective stress on the dislocation segments and of the particular character of the stress versus velocity laws in silicon. The backstresses in the slip plane and in the cross-slip plane are investigated in some detail in the conditions of the upper yield point. A first study of the yield point is also mentioned, which should permit to have a further examination of the well-known model by Alexander and Haasen.

Simulation of Frank-Read sources in silicon

A simulation of dislocation sources in silicon is presented that has been developed in order to examine further how dislocation dynamics and multiplication govern the initial stage of plastic flow in diamond cubic crystals. The numerical method is adapted from an existing code by introducing specific dislocation properties deriving from the presence of strong Peierls forces. The influence of stress and temperature on the dynamics and configurations of Frank-Read sources are examined on {111} sections of model crystals of dimensions larger than 100 μm 2. Most of the results obtained can be qualitatively interpreted in terms of the various contributions to the effective stress on the dislocation segments and of the particular character of the stress vs velocity laws in silicon. The backstresses in the slip plane and in the cross-slip plane are investigated in some detail in the conditions of the upper yield point. These results aim at providing numerical inputs for the recent model on mechanical twinning in semiconductors proposed by Pirouz.

Structural changes in corrosion-resistant steels during hot deformation

1. The hot deformation of corrosion-resistant steels of the ferritic, austenitic, and austenitic—ferritic classes in the 900–1100°C interval at rates\(\dot \varepsilon = 10^{ - 2} - 10^{ - 3} \) sec−1 results in dynamic recrystallization. 2. Various types of substructures are formed in the initial stages of plastic flow, depending on the deformation conditions and the type of crystal lattice of the steels, and, consequently, different mechanisms of dynamic recrystallization are realized. 3. Substructure formation in the initial grains and gradual transformation of low- to high-angle boundaries are the mechanisms responsible for the formation of recrystallized grains in the ferritic steels over the entire temperature region investigated, and in the austenitic-class steel at high temperatures.

溶融炭酸塩型燃料電池のアノード環境下における純Ｃｕ多孔質体の形状安定性

A shrinkage mechamism of anode materials for molten carbonate fuel cells was discussed. Theoretical calculations were made by dividing the shrinkage process into the initial stage of plastic flow and the steady stage of steady-state creep of metals. The results showed that -ln(P0/P) ?? L and e ?? L in the initial stage and e ?? logt in the steady stage; where P0: initial porosity, P:porosity, L:surface pressure load, e:nominal strain and t:time. A model was examined in a H2-CO2-H2O (79-19-2 vol%) mixture gas stream under 2.5-8.9kgf/cm2 at 650°C for 50-1, 000 hours. The anode was porous sintered pure copper (porosity;43±1%) made of spherical gas-atomized powder which was sieved to 74-105μm. The experimental results indicated the proportionality relations mentioned above.

Some observations concerning the initial stage of plastic flow in silicon

physica status solidi (a)Volume 47, Issue 1 p. K17-K20 Short Note Some observations concerning the initial stage of plastic flow in silicon F.-G. Kirscht, F.-G. Kirscht Institut für Physik der Werkstoffbearbeitung, Akademie der Wissenschaften der DDR, Berlin Search for more papers by this authorJ. Doerschel, J. Doerschel Institut für Physik der Werkstoffbearbeitung, Akademie der Wissenschaften der DDR, Berlin Search for more papers by this authorC. Hansch, C. Hansch Institut für Physik der Werkstoffbearbeitung, Akademie der Wissenschaften der DDR, Berlin Search for more papers by this author F.-G. Kirscht, F.-G. Kirscht Institut für Physik der Werkstoffbearbeitung, Akademie der Wissenschaften der DDR, Berlin Search for more papers by this authorJ. Doerschel, J. Doerschel Institut für Physik der Werkstoffbearbeitung, Akademie der Wissenschaften der DDR, Berlin Search for more papers by this authorC. Hansch, C. Hansch Institut für Physik der Werkstoffbearbeitung, Akademie der Wissenschaften der DDR, Berlin Search for more papers by this author First published: 16 May 1978 https://doi.org/10.1002/pssa.2210470144Citations: 3 DDR-1166 Berlin-Rahnsdorf, Seestr. 82, DDR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume47, Issue116 May 1978Pages K17-K20 RelatedInformation

Glide Band Formation in Silicon

Birfringence and etch pit studies of the initial stages of plastic flow in octagonal-shaped silicon crystals oriented for single slip and compressed at low strain rates in the temperature range 750–800 °C show characteristics quite similar to that found for avalanche behavior and ``Luders-band'' type flow in alkali-halide crystals. The narrow glide bands taper to a single plane at opposite ends and the dislocation morphology, as revealed by their phase retardation birefringence characteristics, is in the form of large concentric loops on neighboring planes with staggered sources in the central region of the band. Calculations show that the stress field from dislocation arrays enhances the formation of neighboring arrays by double cross slip and multiplication, and show how different kinds of defects can form. The enhanced shear stress at the cross-slipped segment is significantly greater if the initial source operates on the surface. The effects of partialized dislocations and various dynamic effects which affect the begining and cessation of glide band formation and broadening are shown to be consistent with avalanche behavior.

The failure of polycrystalline iron under plane stress conditions at low temperatures

1. The mechanism of failure of commercial iron is determined by the temperature-force conditions used in testing. At normal temperatures the metal fails by slip without any crack formation, irrespective of the stress conditions: at low temperatures failure is preceded by the development of trans-and intercrystalline microcracks, the space orientation of which depends on the form of the stress state. 2. The statistical distributions of the number and total length of isolated microcracks with respect to their orientation have been constructed from data obtained by the metallographic examination of ruptured specimens. The results show that the orientation of the majority of the microcracks formed in the initial stages of plastic flow is similar to that of the planes on which the maximum tensile stresses act, although microcracks having a substantially different orientation have also been observed. 3. Microcracks do not grow in a straight line within a single grain, but appear as a zigzag line. The distribution of the number and total length of the straight portions of the microcracks with respect to orientation indicates that the mean length of these portions is commensurate with the mean distance between the nonmetallic inclusions. The reason for the change in direction of the microcracks evidently lies in the interaction of the elastic-stress field at the tip of the crack with the elastic-stress field surrounding a nonmetallic inclusion. 4. At low temperatures the appearance of a second tensile stress has a significant effect, leading to a reduction in the ductility of the iron. The effect was most clearly observed at −100°C, at which temperature the maximum slip before failure in uniaxial tension considerably exceeded the maximum slip in biaxial tension. The suggestion is put forward that this effect is due to the smaller degree of opening of the nucleated microcracks in the presence of a second tensile stress.

Elastic-plastic response of a sandwich cylinder subjected to internal pressure

The propagation of plastic zones in a thin-walled sandwich-type cylinder has been analysed theoretically. Boundary conditions are clamped-clamped at both ends, i.e. no rotation is permitted. The material was assumed to behave isotropically and to obey the yieid criterion of Huber-Hencky-von Mises. Deformation was computed on the assumption that the vector of rate of strain was normal to the plastic-interaction curve. The predicted result was verified experimentally. Four specimens were built by lamination of a hexcell core between two concentric cylinders. In the two mild-steel specimens, the initial stage of plastic flow conformed well with the prediction. This proved that plastic flow is not initiated at the mid-position between the end constraints. In two aluminium specimens, this phenomenon of incipient plastic flow could not be observed owing to the absence of a pronounced yield point. The overall agreement was, however, satisfactory.

Some features of metal behavior in the initial stages of plastic flow using the internal friction method

Some features of metal behavior in the initial stages of plastic flow using the internal friction method

Physical theory of the dynamic yield point of crystalline materials

1. The model of viscous damping of high-velocity dislocations leads to a realistic description of the observed macroscopic phenomena during the initial stages of plastic flow of crystalline materials at high deformation rates. It can therefore be asserted that subbarrier dislocation motion makes the primary contribution to plastic flow during these stages of deformation. 2. Data on the damping of elastic shock waves in materials are quantitatively consistent with the damping constant determined by different methods (including the damping of ultrasound). Therefore, data on the damping of elastic shock waves can be used as an independent method for evaluating the ratio of the constant for viscous damping of dislocations to the density of moving dislocations (B/N).

Dislocation dynamics and plastic shear in crystalline solids communication 1

1. Generalization of the experimental data on mobility of dislocations and their capacity to multiply in the process of plastic deformation permits us to describe the basic macroscopic phenomena of plastic flow of crystalline solids, and moreover a good quantitative correspondence of calculation curves of the temperature dependence of fluid-flow stresses with experimental curves has been observed. For crystals distinguished by a high sensitivity of the dislocation velocity to the effective stress, at low tension rates the differences between the magnitudes of the intensity of dislocation multiplication at different low temperatures apparently does not lead to any significant distortion of the lower limit of the yield point. 2. The differential equation found for the mechanical state of the crystal allows us to obtain three special solutions, corresponding to uniaxial deformation with constant velocity, creep, and stress relaxation. The indicated solutions are numerically integrated. In each case series of corresponding curves are obtained. 3. In order to explain the properties of the initial stages of plastic flow within the framework of the calculation model, it is not necessary to introduce concepts of a process of simultaneous freeing of many dislocations or of their breaking away from the atmosphere of impurity atoms. The initial stages of plastic flow can be described by the basic physical parameters characterizing the external conditions and properties of the material in dependence on time.