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DSA

DSA: Dynamic Strain Aging
Definition:Repetitive interaction between mobile dislocations and diffusing solute atoms during the deformation
Explanation:It is well known that both solute atoms and dislocations introduce strain fields in matrix lattices [1]. When these two kinds of defects are adjacent to each other, there is a possibility that their strain fields are compensated and the system is stabilized. In other words, there exists binding between the solute atoms and the dislocations and results in segregation of the solute atoms adjacent to the dislocations (Cottrell atmosphere) [1]. During the deformation at an appropriate range of deformation rate and temperature, mobile dislocations may glide with the velocity similar to the diffusion rate of solute atoms. As a result, the gliding dislocations are repetitively locked by the solute atoms; this phenomenon is termed as DSA.

Since the diffusion of the solute atoms becomes more active at higher temperature and the dislocation mobility decreases with strain rate, higher macroscopic strength of the material results under higher temperature and lower strain rate under DSA. Such property is known as negative strain rate sensitivity (SRS). Moreover, the negative SRS causes the Portevin-Le Chatelier (→PLC) effect, where localised deformation (Fig.1b) is observed and accompanies a serrated flow curve (Fig.1a) [3,4].
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Fig.1 (a) Serrated flow curves observed during tensile deformation of a high Mn steel. (b) Repetitive stress drops are related to deformation band nucleation while the smooth stress increase is related to the band propagation.
SFB-Link:In general, DSA is observed at high temperature where solute atom diffusion is significant. However, serrated flow is observed even at room temperature where long range diffusion of carbon atoms is negligible [5]. Therefore, DSA of high Mn steels is suggested to caused by the rearrangement of C-Mn clusters. Such rearrangement is likely to result from the interaction with stacking faults (→SFs) [6] or that with dislocation cores [7].
References:[1] J.Hirth, J.Lothe, Theory of Dislocations, 1982, John Wiley&Sons, Inc. New York.
[2] G.Dieter, Mechanical Metallurgy, 1988, McGraw-Hill, London.
[3] P.Penning. Acta Metall., 20, pp.1169-1175 (1972).
[4] L.Kubin, Y.Estrin, Acta Metall., 33, pp.397-407 (1985).
[5] L.Chen, H.-S.Kim, B.C.De Cooman, ISIJ Int. 47, pp.1804-1812 (2007).
[6] S.-J.Lee, J.Kim, S.N.Kane, B.C.De Cooman, Acta Mater. 59, pp.6809-6819 (2011).
[7] Y.N.Dastur, W.C.Leslie, Metall. Trans. A, 12A, pp.749-759 (1981).