Fe-Mn based alloys are well known due to several properties [1]. On one hand it was found in the 1980`s that the shape memory effect can be improved by the addition of Si to the binary alloy, mainly for Mn contents smaller than 30 %. This effect is closely related to the presence of the fcc-hcp martensitic transformation. After that a large amount of work has been done in order to improve the shape memory effect by the addition of several other components, like Ni, Co, Cr and also interstitial elements [2,3]. The main reason to invest time and research on shape memory Fe based alloys is the possibility to use the known technology which characterizes the steel industry. Rather recently, it has been shown that Fe-Mn based alloys also belong to the high entropy alloys [4]. These alloys are characterized by the presence of large deformations when large stresses are applied. Once more the martensitic fcc-hcp plays a significant role here, and the magnetic ordering of the austenite might be used to design alloys where the stabilization of the austenite can be better controlled [5]. In order to make proper designs of new alloys showing the mentioned properties it is required to know the effect of adding different components on the main magnitudes related to the fcc-hcp martensitic transformation, like martensitic transformation temperatures, the volume change between the involved phases, the Néel temperature of the fcc austenite, the driving force of the transition, the strain energy opposing it and the stacking fault energy [5, 6, 7, 8]. Some examples of these effects will be presented here concerning the addition of Si, Co and Cr, usual components of the most analyzed alloys. Different strategies to stabilize the austenitic fcc structure will be commented as well as different effects of the para-antiferromagnetic transition of this phase depending on the added component [9].

References

[1] P. La Roca, A. Baruj, M. Sade, “Shape-Memory Effect and Pseudoelasticity in Fe–Mn-Based Alloys”, (2017). Shap. Mem. Superelasticity. 3, 37–48.

[2] Y.H. Wen, H.B. Peng, D. Raabe, I. Gutierrez-Urrutia, J. Chen, Y.Y. Du, NATURE COMMUNICATIONS, 5:4964 (2014) “Large recovery strain in Fe-Mn-Si-based shape memory steels obtained by engineering annealing twin boundaries”

[2] H. Otsuka, Hirohisa Yamada, H. Tanahashi, T. Maruyama, “Shape Memory Effect in Fe-Mn-Si-Cr-Ni Polycrystalline Alloys” Materials Science Forum (Volumes 56-58),1990, 655-660

[4] Z. Li, K. G. Pradeep, D. Raabe, “Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off”, Nature volume 534, pages 227–230 (2016)

[5] M. D. Acciarri, P. La Roca, L. M. Guerrero, A. Baruj, J. Curiale, M. Sade, Effect of FCC anti-ferromagnetic ordering on the stability of phases in Fe60-xMn30Cr10Cox high entropy alloys, Journal of Alloys and Compounds 823 (2020) 153845.

[6] F. Malamud, L.M. Guerrero, P. La Roca, M. Sade, A. Baruj, Role of Mn and Cr on structural parameters and strain energy during FCC-HCP martensitic transformation in Fe-Mn-Cr shape memory alloys, Mater. Des. 139 (2018) 314-323

[7] L.M. Guerrero, P. La Roca, F. Malamud, A. Baruj, M. Sade, Composition effects on the fcc-hcp martensitic transformation and on the magnetic ordering of the fcc structure in Fe-Mn-Cr alloys, Mater. Des. 116 (2017) 127-135

[8] L.M. Guerrero, P. La Roca, F. Malamud, A. Baruj, M. Sade, Experimental determination of the driving force of the fcc-hcp martensitic transformation and the stacking fault energy in high-Mn Fe-Mn-Cr steels, J. Alloys Compd. 797 (2019) 237-245

[9] L.M. Guerrero, P. La Roca, F. Malamud, A. Butera, A. Baruj, M. Sade, “Strategies to increase austenite FCC relative phase stability in High-Mn steels”, Journal of Alloys and Compounds, Volume 854, 2021, 156971