PSI - Issue 64

Maryam Mohri et al. / Procedia Structural Integrity 64 (2024) 376–383 M.Mohri et al./ Structural Integrity Procedia 00 (2019) 000–000

382

7

than the as-received one (385 MPa), attributed to the presence of carbide precipitates which augment the motion of partial dislocations by elevating the back stresses. Moreover, Fig. 5 illustrates an increase in recovery stress after the second training cycle, followed by a decrease in the third cycle. This enhancement in recovery stress is attributed to an improved reversibility from the martensite phase to the austenite phase during heating. This enhanced reversibility post-aging and training is due to the generation of very fine variant martensite induced by strain (Mohri et al. (2023)), contrasting with the thick and multi-variant martensite plates prevailing in the absence of precipitates. Deformation at room temperature not only results in martensite formation but also in the generation of a certain amount of SFs and dislocation gliding, representing irreversible plastic strain. Some of the martensite phase formed during the stress-induced martensite transformation under loading conditions can revert to austenite (i.e. SE), with further recovery occurring during heating (i.e. SME). With an increase in the number of training cycles, due to the formation of a higher fraction of martensite and dislocations and their interactions, the movement and rearrangement of Shockley partial dislocations are delayed (Mohri et al. (2022)). This delay suppresses the martensite-to-austenite transformation, consequently increasing phase transformation temperatures and reducing the effectiveness of the SME. 4. Conclusion In conclusion, this research has delved into the intricate interplay between thermomechanical treatment, microstructure evolution, and functional properties, particularly the recovery stress induced by the shape memory effect, in an Fe-based shape memory alloy with a specific composition. The investigated Fe-based shape memory alloy, Fe–17Mn–5Si–10Cr–4Ni–1(V,C) %Wt., holds promise for various civil engineering applications due to its robust SME and suitable mechanical properties. The thermomechanical treatment significantly influenced the microstructure, resulting in enhanced shape memory effect and recovery stress. Notably, the presence of VC precipitates played a crucial role in augmenting the shape memory properties, facilitating the reversible transformation between martensite and austenite phases. Moreover, the investigation into the thermomechanical behavior revealed intriguing dynamics in recovery stress during thermal cycling. The findings showcased an increase in recovery stress following both heat treatment and thermomechanical training, underscoring the importance of precipitation strengthening and fine martensite variants in enhancing reversibility and recovery stress. Overall, this research contributes to the deeper understanding of the thermo-mechanical processing effects on Fe based shape memory alloys, paving the way for their optimized utilization in various engineering applications. The insights gained from this study can inform the design and development of advanced shape memory materials with tailored properties for specific engineering requirements, thereby advancing the field of smart materials and structures. Acknowledgements The authors acknowledge the Innosuisse Swiss Innovation Agency for funding this research project (project number 56959.1 IP-ENG). The financial and technical support from the project partners, namely Hilti AG, Schaan, Liechtenstein and re-fer AG, Switzerland are highly appreciated. Any opinion and findings in this paper are those of the authors and do not necessarily reflect the view of the sponsors. References Arabi-Hashemi, A., Lee, W. and Leinenbach, C.,2018. Recovery stress formation in FeMnSi based shape memory alloys: Impact of precipitates, texture and grain size. Materials & Design 139: 258-268. Baruj, A., Bertolino, G. and Troiani, H.,2010. Temperature dependence of critical stress and pseudoelasticity in a Fe–Mn–Si–Cr pre-rolled alloy. Journal of alloys and compounds 502(1): 54-58. Baruj, A., Kikuchi, T. and Kajiwara, S.,2004. TEM observation of the internal structures in NbC containing Fe–Mn–Si-based shape memory alloys subjected to pre-deformation above room temperature. Materials Science and Engineering: A 378(1-2): 337-342. Baruj, A., Kikuchi, T., Kajiwara, S. and Shinya, N.,2004. Improvement of shape memory properties of NbC containing Fe–Mn–Si based shape memory alloys by simple thermomechanical treatments. Materials Science and Engineering: A 378(1-2): 333-336.