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Serrated flow in alloy systems


Although the notion of “plastic flow” evokes a smooth process, agreeing with one’s everyday experience and, more specifically, with the common examples of smooth deformation curves shown to students during the lessons on mechanics, plastic deformation often proceeds in an intermittent manner. The serrated flow is one of the striking features of plastic flows in solids, which reveals a self-organized nature of the dynamics of crystal defects and unifies the problems of plasticity with diverse phenomena observed in complex systems of various nature. While such an instability of a smooth plastic flow may be caused by different mechanisms and can occur in various materials, the most abundant examples of this phenomenon have been documented for a wide range of alloys, for which the discovery of intermittent deformation will soon celebrate the 200-year anniversary. It is therefore not surprising that the serrated flow is also an essential feature of the deformation behavior exhibited by high-entropy alloys and has quickly attracted the attention of the researcher community. To provide a comprehensive approach to this problem, this chapter is subdivided into two parts. The first part presents the serrated flow in traditional alloys – the Portevin-Le Chatelier (PLC) effect. It is caused by the interaction of dislocations with solute atoms, which is dynamic in the sense that the solutes do not simply represent immobile obstacles but diffuse and form clouds on the dislocations, so that the respective pinning force depends on the dynamics of all actors. The attention to this effect in the present book is due to numerous proofs that although the subdivision into basic and solute elements is not evident for HEAs, the PLC instability seems to be the mechanism of serrated flow in such alloys in a wide range of experimental conditions. Moreover, the PLC effect served as a model object for the elaboration of various mathematical approaches to testing the complexity of distinct behaviors of plastic deformation. Some of them are presented in detail in the first part. As the respective literature is huge, it is not reviewed systematically. Instead, the authors put an accent on providing the reader with a qualitative knowledge of the basic dynamical regimes uncovered by virtue of the analysis of experimental data obtained on multiple scales. It is the second part that is devoted to the serrated flow in the high-entropy alloys (HEAs). As this field of research is quickly growing, the challenge is to present a synthesis of different findings published since the beginning of the investigations. It occurs that besides an analog of the PLC effect, other mechanisms, e.g., twinning, may also lead to plastic instability in distinct experimental conditions. Since these mechanisms are only shortly evoked in the first part, it should be underlined here that they also operate in traditional alloys, albeit the analysis of this analogy remains beyond the scope of the book. Formally, the chapter is organized so that the second part makes use of some explanations given in the first part. Nevertheless, it can be read independently due to providing enough detail on both the history of the problem, under a complementary angle, and the methods of analysis. It may only be noted that the description of the mathematics of the multifractal analysis is not resumed in the second part. However, a succinct explanation of the physical meaning of this analysis allows for the understanding of experimental conclusions without referring to a comprehensive description in the first part.
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Dates and versions

hal-03816482 , version 1 (16-10-2022)



M.A. Lebyodkin, Tatiana A Lebedkina, Jamieson Brechtl, Peter K Liaw. Serrated flow in alloy systems. High-Entropy Materials: Theory, Experiments, and Applications, Springer, pp.523-644, 2021, 978-3-030-77640-4. ⟨10.1007/978-3-030-77641-1_11⟩. ⟨hal-03816482⟩
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