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MBIP

MBIP: Microband Induced Plasticity
Definition:Mechanical property enhancement in a medium to large strain regime due to microband formation in high Mn steels with a relatively high staking fault energy.
Explanation:When Al is introduced in a high Mn steel, it effectively increases stacking fault energy (→SFE) [1] of the steel and twinning becomes unlikely to occur during deformation. Moreover, planar glide is generally observed, resulting in a Taylor lattice structure delineated by dense dislocation walls in the early deformation stage [2-6]. As the deformation continues, dense dislocation walls become more pronounced in order to accommodate misfit between the domains; among these structures, a set of parallel dislocation walls is termed a microband [3,4] (Fig.1a). Until now, the SFE of reported steels showing microbands is in the range of 60-80 mJ m-2 [4,5].

Park et al. suggested that the ductility can be enhanced by the microbands in region II (Fig.1b) by the formation and intersection of the microbands [4]. On the other hand, Gutierrez-Urrutia and Raabe explained the flow stress evolution in a Fe-30.5Mn-2.1Al-1.2C steel by dislocation substructures as well as twinning, and claimed that the microbands do not play a significant role in strain hardening [5].

Hence, more investigation is necessary to identify the stress state and strain range where microband is generated and influence mechanical properties of the steel. Moreover, the interaction between microbands and the kappa-carbide should be studied, since they both form when Al is added to the steel.
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Diagram:

Figure 1. (a) TEM micrographs of microbands observed in a Fe-28Mn-9Al-0.8C(wt%) steel adopted from [4]. (b) Stress-strain and strain hardening rate-strain curves of a fully austenitic Fe-28Mn-10Al-1.0C (wt%) steel adapted from [5].
SFB-Link:MBIP mechanism seems to be closely related to SFE and can compose deformation mechanism map.

MBIP can occur along with TWIP depending on the SFE of an alloy.

The steels showing MBIP present excellent mechanical properties. Employing the future knowledge on the strain hardening mechanism, the materials with high strength as well as ductility can be systematically designed.
References:[1] A. Saeed-Akbari, J. Imlau, U. Prahl, and W. Bleck, Met. Mater. Trans. A, 40A, 2009, p.3076.
[2] D. Kuhlmann-Wilsdorf, Mater. Sci. and Eng., A113, 1989, p.1.
[3] J. Yoo and K.-T. Park, Mater. Sci. and Eng., A496, 2008, p.417.
[4] K.-T. Park, G. Kim, S. Kim, S. Lee, S. Hwang and C. Lee, Met. Mater. Int., 16, 2010, p.1.
[5] I. Gutierrez-Urrutia and D. Raabe, Acta Mater. 60, 2012, p.5791.
[6] I. Gutierrez-Urrutia and D. Raabe, Acta Mater. 68, 2013, p.343.