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ODUCTION

FE-MN-SI-BASED shape memory alloys (SMAs) are considered for engineering applications because of their good workability, machinability, weldability, damping capacity, and their low cost. Sato et al. first reported that monocrystalline Fe-30Mn-1Si SMA showed an excellent shape memory effect (SME), i.e., an ~ 9 pct recovery strain.[1] However, solution-treated polycrystalline Fe-Mn-Si-based SMAs only achieved a recovery strain of 2 to 3 pct,[2,3] which does not meet the requirements of engineering applications. Many attempts have been made to improve the recovery strain of Fe-Mn-Sibased SMAs, i.e., by tuning the alloy composition,[2,4,5] training,[6,7] thermomechanical treatments,[8–11] ausforming,[12–15] adding interstitial atoms,[16–19] precipitating particles,[20–23] melt spinning,[24] casting,[25–27] and utilizing the d fi c phase transformation.[28] To date, the most successful case is that Wen et al. obtained the bending recovery strain of 8.4 pct and tensile recovery strain of 7.6 pct in an annealed cast polycrystalline

HUABEI PENG, LIQIU YONG, and YUHUA WEN are with the School of Manufacturing Science and Engineering, Sichuan University, Chengdu 610065, P.R. China. Contact e-mail: [email protected] SHANLING WANG is with the Analytical and Testing Center, Sichuan University, Chengdu 610065, P.R. China. Contact e-mail: [email protected] Manuscript submitted November 2, 2018.

METALLURGICAL AND MATERIALS TRANSACTIONS A

Fe-20.2Mn-5.6Si-8.9Cr-5.0Ni alloy.[27] Casting is a cost-efficient manufacturing technique, and it is especially suitable to fabricate components with complex shapes. Thus, cast Fe-Mn-Si-based SMAs are the most favorable for large-scale production. Although cast Fe-Mn-Si-based SMAs hold great promise for engineering applications, this approach is not attracting worldwide attention from researchers. There are only a small number of post-studies on cast Fe-Mn-Si-based SMAs. For example, Peng et al. investigated the effect of Mn contents on the solidification mode of cast Fe-Mn-Si-based SMAs, and subsequently established a set of Creq and Nieq equations to predict their solidification modes.[29,30] In addition, Wang et al. reported that grain refinement by adding titanium deteriorates the shape memory effect of cast Fe-Mn-Sibased SMAs.[31] Furthermore, Peng et al. demonstrated that coarsening austenitic grains is a key criterion for achieving large recovery strains in cast polycrystalline Fe-Mn-Si-based SMAs.[32] It should be noted that an annealing treatment is a simple way to tailor properties of castings. Wen et al. reported that the evolution of lathy d-ferrite with an annealing treatment influenced the shape memory effect of a cast Fe-18Mn-5.5Si-9.5Cr-4Ni SMA.[33] However, the existence of d-ferrite obscures the effect of annealing treatment on other microstructures in cast Fe-Mn-Si-based SMAs. Therefore, we selected an Fe-18.54Mn-5.70Si-8.91Cr-4.45Ni SMA, which is nearly free of d-ferrite, to clarify the correlation between annealing treatments and the shape memory effect.

II.

EXPERIMENTAL