Kinetics of deformation fronts during serrated Lüders deformation in α-iron at high temperature

Abstract

At room temperature, the deformation of most bcc metals, which contain a small amount of interstitial elements, is accompanied by the formation of a Lüders band and its monotonic propagation over the tensile yield area. Within the framework of the autowave concept, front of the Lüders band is a switching autowave, which realizes the transition from a metastable elastically deformable state to a stable plastically deformable state. However, in the temperature range of blue brittleness of mild steels of 423 – 510 K, when the interaction of atoms of the dissolved substance with mobile dislocations takes place, propagation of the Lüders band is accompanied by a discrete flow. The patterns of propagation of the Chernov-Lüders fronts in ARMCO iron in the temperature range from 296 to 503 K and strain rates from 6.67·10–6 to 3.7·10–2 s–1 are considered in this paper. It was established that under these conditions both monotonic and discrete kinetics of front movement can be realized. Regardless of the movement nature, the Lüders deformation and width of the front remain unchanged throughout the entire process. The local strain rate at the front depends on magnitude of the effective stress, and with monotonic kinetics it increases with stress according to an exponential law, and with discrete kinetics it increases according to a linear law. This difference is due to different autowave modes that are formed in this case. The autowave of localized plasticity switching corresponds to monotonic kinetics, and the autowave of excitation – to discrete kinetics.