Types of Localization of Plastic Deformation and Stages of Loading Diagrams of Metallic Materials with Different Crystalline Structures

Abstract

Macrolocalization, which accompanies the process of plastic deformation beginning from the yield point and ending by fracture, is determined by the staged character of material-loading diagrams. The evolution of localization patterns in a plastic flow of body-centered cubic vanadium alloy, hexagonal close-packed magnesium alloy, tetragonal tin, and face-centered cubic submicrocrystalline aluminum is analyzed within this concept.Introduction. It was found [1-3] that macrolocalization accompanies the process of shape variation of all materials, independent of their chemical nature, crystallographic state, and real structure, over the entire process from the yield point to fracture. The types of deformation localization have a uniform dependence on the law of strain hardening of the material (loading diagram) and uniformly change from one stage to another. The number of such types is limited. Four types are known at the moment [3]: 1) single moving deformation fronts (autowaves of excitation or switching); 2) equidistant moving zones of deformation localization (phase autowave); 3) spatially periodic steady distributions of deformation-localization sites (stable dissipative structures); 4) high-amplitude motionless deformation sites. The first type is typical of stages of easy slip of single crystals and yield areas of polycrystalline materials. The stages of linear hardening correspond to the second type of localization in the form of phase autowaves. The third type of localization arises at stages of parabolic hardening. High-amplitude steady zones of deformation localization in regions of future viscous fracture were observed when the strain before the beginning of neck formation was several percent of the total strain. The evolution of localization patterns rigorously follows the stages of the strain curves. If some stage is absent, the corresponding type of localization is absent as well. Therefore, it was only the third type of macrolocalization that was observed in all experiments without any exceptions, which were performed with single and polycrystals, pure metals and high alloys, ordered structures, materials with dislocation and twinning mechanisms of deformation, alloys with phase-change plasticity, and substances with viscous and quasi-brittle fracture [3]. The phenomenology of transformation of the first to the second type of localization [4] and from the second to the third type of localization [5] has been described. It remains unclear, however, how a steady dissipative structure (third type) is transformed to a distribution with one high-amplitude maximum.

Kinetics of localized plastic flow during deformation and fracture of a D1 alloy

“…4 that the beam of the trajectories of the localized plastic flow domain is formed during deformation of a D1 alloy as well. These data and the results obtained in [3,[8][9][10] enable both the point of fracture and the service life of the specimen to be predicted.…”

Special features of the localized plastic deformation and fracture of high-chromium steel of the martensitic class

“…As was shown in [4][5][6], the kinetics of the localized-strain centers in the prefracture stage governs the entire tough-fracture process.…”

Plastic macrodeformation of polycrystalline and submicrocrystalline titanium for biomedical applications

“…In coarse-grained and submicrocrystalline titanium, plastic flow have different sets of stages. An analysis of the stages was performed by logarithmation [6]. To identify stages, we used the value of the strain-hardening index n included in the Taylor equation [8] for approximating strain curves of the general type:…”

“…In this case, the portion of the strain curve with n = 1 corresponds to linear hardening, the portion with n ≈ 0.5 to parabolic Taylor hardening, and the portion with n < 0.5 to prefracture [6,7,9]. An analysis of the stages of the stress-strain curve of coarse-grained titanium shows that the ascending portion of the curve corresponds to a short stage of linear hardening at 0.008 ε 0.014, a stage of Taylor hardening with a strain-hardening index n = 0.56 at 0.019 ε 0.041, and a stage with n ≈ 0.4 at 0.075 ε 0.160.…”

“…For both materials at the prefracture stage, the diagrams of motion of the deformation zone are bundles of lines converging to the focal point (X s , t f ) (t f is the time of deformation to fracture). Fracture of the specimens occurs in the stationary localization zone [6,9].…”