Stasis mechanism of γ → ε martensitic transformation in Fe-17Mn alloy

Hong, Jin Sung; Choi, Seon Min; Lee, Young Kook

doi:10.1016/j.actamat.2021.116846

Cited by 12 publications

(3 citation statements)

References 46 publications

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“…This result is coherent since after a rapid growth, the highest transformed fraction was found around cycle 8. This SEM characterization confirmed the previously commented stasis phenomenon [118]; the martensite fraction never reached a fully transformed austenite. On the other hand, the observed ε martensitic transformation showed a fully reversible behavior, because no α′ martensite was created at the intersection of the ε plates on cycling.…”

Section: Thermal Cycling Behaviorsupporting

confidence: 89%

“…As the density of dislocations rises, the stress field makes the nucleation of the martensite difficult and, being a nonthermoelastic alloy, exacerbates the apparition of local plastic deformation in the matrix [31] and in the γ/ε interfaces [116]. Hence, the growth of the martensite variants is hindered, resulting in a stasis mechanism in which the transformed volume fraction does not reach the 100% [117,118]. This phenomenon also leads to a delay in the MT, which agrees with the shift of the IF peaks because the transformation requires a longer overcooling to get started.…”

Section: Thermal Cycling Behaviormentioning

confidence: 99%

“…Since the density of nucleation points grows on cycling, creating an stress field that hinders the nucleation and movement of the variants, a higher driving force is needed for the forward transformation to begin, and therefore, Ms decreases [89]. Despite the controversy on the Mf, Af and As temperature shift [118], this result has been widely observed for ternary Fe-Mn-Si [89] and quinary Fe-Mn-Si-Cr-Ni [65], including additive manufactured alloys [54]. In parallel, to follow the evolution of the microstructure along the cycling behavior, an equivalent sample was equally cycled for its observation at SEM.…”

Section: Thermal Cycling Behaviormentioning

confidence: 99%

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Additive Manufacturing of Fe-Mn-Si-Based Shape Memory Alloys: State of the Art, Challenges and Opportunities

Del-Río,

Nó,

Gómez

et al. 2023

Materials

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Additive manufacturing (AM) constitutes the new paradigm in materials processing and its use on metals and alloys opens new unforeseen possibilities, but is facing several challenges regarding the design of the microstructure, which is particularly awkward in the case of functional materials, like shape memory alloys (SMA), as they require a robust microstructure to withstand the constraints appearing during their shape change. In the present work, the attention is focused on the AM of the important Fe-Mn-Si-based SMA family, which is attracting a great technological interest in many industrial sectors. Initially, an overview on the design concepts of this SMA family is offered, with special emphasis to the problems arising during AM. Then, such concepts are considered in order to experimentally develop the AM production of the Fe-20Mn-6Si-9Cr-5Ni (wt%) SMA through laser powder bed fusion (LPBF). The complete methodology is approached, from the gas atomization of powders to the LPBF production and the final thermal treatments to functionalize the SMA. The microstructure is characterized by scanning and transmission electron microscopy after each step of the processing route. The reversibility of the ε martensitic transformation and its evolution on cycling are studied by internal friction and electron microscopy. An outstanding 14% of fully reversible thermal transformation of ε martensite is obtained. The present results show that, in spite of the still remaining challenges, AM by LPBF offers a good approach to produce this family of Fe-Mn-Si-based SMA, opening new opportunities for its applications.

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Section: Thermal Cycling Behaviorsupporting

confidence: 89%