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

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1. Introduction

Nomenclature SMAs

Shape memory alloys

SE

Super-elasticity

SME

Shape memory effect

Fe-SMAs Iron-based SMAs SEM

Scanning electron microscope Austenite start formation temperature Austenite finish formation temperature

A s A f ε se ε el ε ul E

SFs

Stacking faults

Super-elasticity strain

Elastic strain Unloading strain Yield strength Young's modulus

HCP FCC

Hexagonal close-Packed Face-centered-cubic

1.1. Shape Memory Alloys Shape memory alloys (SMAs) are materials capable of reverting to their original shape even after enduring significant strain, achieved either by alleviating stress (referred to as super-elasticity or SE) or by heating (known as the shape memory effect (SME)) (Otsuka et al. (1986)). Among SMAs, Iron-based SMAs (Fe-SMAs) have garnered significant interest in the past decade due to their favorable shape memory behavior, impressive mechanical properties (such as stable recovery stresses and acceptable elastic modulus), and cost-effectiveness (Sato et al. (1982), Sato et al. (1984), Ghafoori et al. (2017)), warranting their application in civil engineering on a large scale. The discovery of the SME in Fe-Mn-Si-based SMAs by Sato et al. (1982) marked a crucial milestone, establishing them as a significant group of shape memory materials. A novel composition of Fe-SMA, denoted as Fe–17Mn–5Si–10Cr–4Ni–1(V,C) %Wt. with nano-sized VC, has been developed for applications in civil engineering (Dong et al. (2009), Leinenbach et al. (2012)). This alloy was specifically formulated and optimized to exhibit a robust SME rather than SE, with the aim of utilizing it for pre-stressed strengthening of civil structures. Studies investigating various aspects including phase transformation (Czaderski et al. (2014)), recovery stress and strain (Lee et al. (2013)), SE (Mohri et al. (2023), Khodaverdi et al. (2022), Mohri et al. (2022)), cyclic properties (Golrang et al. (2024)), and fatigue performance (Ghafoori et al. (2017) of this Fe-SMA indicate its suitability as a pre-stressing element in civil infrastructure projects Lee et al. (2013), Czaderski et al. (2014)). Earlier studies have illustrated that near the VC precipitates, a substantial elastic strain field emerges, thereby enhancing both the SME and SE. Additionally, these VC precipitates serve as preferred nucleation sites for the ε -phase and promote a dense distribution of stacking faults within the austenite matrix (Dong et al. (2009), Leinenbach et al. (2012)). Furthermore, research indicates that specific textures can augment the SME and SE behavior of this alloy (Leinenbach et al. (2017), Arabi-Hashemi et al. (2018)). Previous research has indicated that a thermomechanical treatment, involving slight deformation at room temperature followed by annealing above the A f temperature (the temperature at which austenite formation finishes), has shown to enhance the SME and SE of Fe-Mn-Si-based alloys (Chung et al. (1996), Khalil et al. (2013), Mohri et al. (2022), Mohri et al. (2023)). It has been observed that pre-rolling solution-annealed austenite combined with aging treatment in Fe–Mn–Si-based alloys containing C and Nb resulted in improved shape memory properties. The microstructure of specimens subjected to this treatment displayed well-distributed NbC particles and a high density of stacking faults in the austenite phase, which interacted to enhance shape memory properties (Baruj et al. (2004)). Similarly, in another investigation, a simple thermomechanical treatment applied to an Fe–Mn–Si–Cr SMA, involving rolling at 600 °C followed by a 10-minute aging process at 800 °C, induced significant SE behavior around 100 °C.