Dynamics of deformation bands initiated by impact of an indenter on the surface of aluminum-magnesium alloy

Abstract

The dynamics of macrolocalized deformation bands generated by the impact of a Vickers indenter on the surface of an AlMg6 aluminum-magnesium alloy deformed under creep conditions was studied by high-speed video recording and acoustic emission methods. It has been established that these bands are the trigger for the development of a macroscopic jump in plastic deformation on the creep curve. It is shown that in alloys exhibiting the Portevin-Le Chatelier effect it is necessary to take into account the initiation and propagation of deformation macrobands during surface erosion damage and to estimate the volume and morphology of the plastic zone during impact microindentation of a deformable alloy. Keywords: intermittent deformation, deformation band, impact, indenter, aluminum-magnesium alloy.

Nonlinear dynamics of an individual Portevin--Le Chatelier deformation bands

“…The optical method used is similar to the shadow method of [4] modified in two aspects: more than three orders of magnitude increase in the speed of video recording and the use of computer processing of digital images by program subtraction of successive images. This method of image processing [22] allows highlighting the contours of items (bands or cracks) moving with speeds greater than the threshold speed. Acoustic emission signals were measured using the Zetlab BC-601 AE sensor with almost flat amplitude frequency response in the frequency range of ∼ 100−800 kHz and smooth decrease in the lower frequency range, < 100 kHz.…”

“…Discontinuous deformation of metals and alloysthe Portevin-Le Chatelier (PLC) effectis a vivid non-linear phenomenon in the physical material science that consists in spontaneous (self-organizing) autolocalization of plastic deformation in dynamically determined situations with defined deformation rate ε0 or stress rate σ0 , respectively [1][2][3][4][5][6][7]. The interest in discontinuous deformation and band generation is related not only to the study of non-linear effects in the macrokinetics of plastic materials due to spatial-time self-organizing of large dislocation ensembles, but also to the practical application of metal alloys demonstrating the PLC effect (alloys based on aluminum, copper, titanium, zirconium, medium-alloyed steel, etc., in particular, hightechnology aluminum alloys used in aerospace and transport industries).…”

“…The interest in discontinuous deformation and band generation is related not only to the study of non-linear effects in the macrokinetics of plastic materials due to spatial-time self-organizing of large dislocation ensembles, but also to the practical application of metal alloys demonstrating the PLC effect (alloys based on aluminum, copper, titanium, zirconium, medium-alloyed steel, etc., in particular, hightechnology aluminum alloys used in aerospace and transport industries). Macroscopically localized deformation bands compromise surface quality of industrial products, cause local corrosion and directly participate in the mechanism of the main crack initiation and development [8][9][10].…”

“…Video recording with a rate of 500 fps and a resolution of 8 µm/px has shown that type B " jerking" band is a time-spatial structure composed of several deformation bands, each, except the primary (mother) band, nucleating at the boundary of the preceding band and expanding in such a way that its " center of gravity" remains immobile. As a result of the deformation hand-off from one band to another, when a new band is nucleated at the boundary of the preceding band, the macro-localized deformation propagates along the direction of sample expansion [6,16].…”

“…Further increase in the rate of video recording of the deformed sample up to 5000 fps made it possible to identify a stage of growth of the embryo band in the direction of maximum tangential stresses that make an angle of 58−63 • to the expansion axis [17][18][19], while video recording with a rate of 25 000 fps shows the elliptical shape of the embryo band outline and speed jerks of its tip and the moment of reaching the opposite side surface of the sample, i.e., the moment when a complete deformation band is formed [20,21]. Typical times in the evolution of the embryo band ∼ 0.1−1 ms are less than the build-up time of the subsequent stress drop (∼ 1−3 ms), and hence, they are considerably shorter than the time interval between the drops.…”