Fe-based Shape Memory Alloys Research Articles

Microstructure and Shape Memory Properties of Gas Tungsten Arc Welded Fe-17Mn-5Si-10Cr-4Ni-(V, C) Shape Memory Alloy.

In this study, microstructure, mechanical, and shape memory properties of the welded Fe-based shape memory alloy (Fe-SMA) plates with a nominal composition of Fe-17Mn-5Si-10Cr-4Ni-(V, C) (wt.%) by gas tungsten arc welding were investigated. The optimal heat input to ensure full penetration of the Fe-SMA plate with a thickness of 2 mm was found to be 0.12 kJ. The solidified grain morphology adjacent to the partially melted zone was columnar, whereas the equiaxed morphology emerged as solidification proceeded. The ultimate tensile decreased after welding owing to the much larger grain size of the fusion zone (FZ) and heat-affected zone (HAZ) than that of the base material (BM). Weldment showed lower pseudoelastic (PE) recovery strain and higher shape memory effect (SME) than those of the plate, which could be ascribed to the large grain size of the FZ and HAZ. Recovery stress (RS) slightly decreased after welding owing to lower mechanical properties of weldment. On the other hand, aging treatment significantly improved all PE recovery, SME, and RS via carbide precipitation. Digital image correlation analysis revealed that HAZ showed the lowest SME after heating and cooling, implying that the improved SME of FZ compensated for the low SME of the HAZ.

Adapting the Mn content within a Fe-Mn-Si-based shape memory alloy by in situ parameter variations in laser-based additive manufacturing

Shape memory alloys exhibit unique properties ideal for functionally integrated components, such as actuators. While commonly used Ni-Ti alloys are well established, especially in biomedicine and aerospace, their high cost limits wider applications. Fe-based shape memory alloys present an affordable alternative, suitable for diverse applications, with a larger thermal hysteresis but lower recovery strain. Nonetheless, their functional properties can be enhanced through optimized processing methods like laser powder bed fusion and adjustments to their alloy composition. In the present study, laser powder bed fusion was used for modifying the composition and microstructure of a Fe-30Mn-6Si-5Cr alloy. For this purpose, laser parameters were varied to evaporate up to 47.3% of the initial Mn in the manufacturing process. In this context, the amount of Mn evaporated was dependent on both the line energy and more considerably on the volume energy density introduced in the manufacturing process. Subsequently, the impact of the resulting compositional changes on the microstructure was analyzed, and the functional properties were visualized using a demonstrator. Lowering the Mn content below 24.1% led to a higher degree of ferrite in the otherwise austenitic microstructure. This also affected the functional properties. These findings highlight the potential of laser-based additive manufacturing for modifying the composition and microstructure of shape memory alloys in situ and, thus, tailoring their functional properties.

A Novel Technique for Improving Cyclic Behavior of Steel Connections Equipped with Smart Memory Alloys.

Residual drifts are an important measure of post-earthquake functionality in bridges and buildings, and can determine whether the structure remains fit for its intended purpose or not. This study aims at investigating numerically, through finite element (FE) analysis in ABAQUS, the cyclic response of exterior steel I beam-hollow column connection using welded shape memory alloys (SMA) bolts and seat angles. This is followed by validating the numerical model using an accredited experimental data available in the literature through different techniques, (1) SMA bolts, (2) SMA angles, (3) SMA bolts and angles. The parameters investigated included: SMA type, SMA angle thickness, SMA bolt diameter, SMA angle stiffener and SMA angle direction. The cyclic performance of the steel connection was enhanced further by varying the bolt diameter, plate thickness, angle type and direction. The results revealed that the connections equipped with a combination of SMA plates and SMA angles reduced the residual drift by up to 94%, and doubled the self-centering capability compared to conventional steel connections. Moreover, the parametric analysis showed that Fe-based SMA members could be a good alternative to NiTi based SMA members for improving the self-centering capability and reducing the residual drifts of conventional steel connections.

Effect of Gd, V, and Y Alloying on the Corrosion Properties of Fe-Mn-Ni-Al Fe-based Shape Memory Alloy

Shape Memory Alloys (SMA) are widely utilized in numerous industrial applications nowadays. Significant attention has been given to Fe-based SMA in civil engineering applications due to their high strength and reasonable cost. Researchers are striving to improve the corrosion resistance of these alloys so they can be utilized in marine environments. This article focuses on the effect of Gd, V, and Y alloying on FeMnNiAl based SMA. The phases and morphological effects were characterized using X-Ray diffractometer (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS). To examine the corrosive nature of the Fe-based SMA system, a potentiodynamic analysis and electrochemical impedance spectroscopy (EIS) tests were performed in 3.5% NaCl solution. Results show that the addition of Gd rare earth metal has improved the overall corrosion efficiency of Fe-based SMAs by 48%.

Experimental study on bonding properties of Fe-SMA-to-steel bonded interface

The interfacial bonding performance between Fe-based shape memory alloys (Fe-SMA) and steel is of utmost importance for the reinforcement of steel structures using Fe-SMA. In order to better reveal the bonding performance and ensure the reliability of Fe-SMA-to-steel bonded interfaces, the single-lap-shear tests of 27 adhesive joints were conducted. The experimental results indicate that the bearing capacity increases with the bonding length until reaching the effective bonding length (Le), with SA, Sika, and LC adhesive joints possessing Le of around 90 mm, 90 mm, and 100 mm, respectively. Better bonding performance can be achieved with 1–1.5 mm thickness for the 3 types of adhesive joints, while the bearing capacity of LC adhesive joints is less affected by the adhesive thickness. The SA joints experienced interface debonding failure, the Sika joints experienced the mixed failure mode of interface debonding and cohesive failure, and the LC joints exhibited cohesive failure. For the bonded interfaces, cohesive failure is the preferred mode, evidenced by Fe-SMA plates in LC joints reaching 60% of their tensile strength at failure. Furthermore, utilizing the established constitutive model of Fe-SMA and the strain propagation from experiments, the shear stress evolution and interfacial bond-slip relationship of Fe-SMA-to-steel bonded interfaces were analyzed, demonstrating that the nonlinear behavior and high ductility of Fe-SMA significantly affect the load-bearing performance and failure evolution. This paper verifies the feasibility of reinforcing steel structures with Fe-SMA through adhesive bonding connection, providing an experimental basis for the theoretical analysis and practical application of Fe-SMA-to-steel bonded interfaces.

Corrosion resistance of VC-reinforced Fe-based SMA coatings by laser cladding

The corrosion resistance of 42CrMo steel is insufficient to meet the demands in the marine environment, despite its widespread application in bearings and other fields. Herein, Fe-Mn-Si-Cr-Ni-χ(VC) shape memory alloy (SMA) composite coatings were successfully fabricated on the surface of 42CrMo steel using laser cladding technology. The results present that the coatings are mainly composed of γ austenite (fcc) phase and ε martensite (hcp) phase. Based on research findings, the incorporation of VC has been found to promote the γ → ε martensite phase transition in shape memory alloys. Simultaneously, electrochemical tests were conducted on 42CrMo substrate and SMA coating in 3.5 wt% NaCl solution. It was found that the coatings doped with an appropriate amount of VC could effectively enhance its corrosion resistance. When the doping amount of VC reaches 1.5 wt%, the charge transfer resistance (Rct) is significantly higher than that of the 42CrMo substrate and the pure SMA coating, as well as that of the coating doped with 2.0 wt% VC, reaching 21, 2.6, and 3.3 times of them, respectively. The charge transfer resistance Rct of LS1.5 is much higher than that of 42CrMo, LS0, and LS2.0, reaching 21, 2.6, and 3.3 times, respectively. Additionally, the maximal polarization resistance (Rp) of coatings achieves 4.39 times that of 42CrMo. This study points out that VC can efficiently boost the corrosion resistance of SMA composite coatings and may have uncovered a novel approach for improving the surface corrosion resistance of medium carbon steel.

Effect of thermomechanical training on recovery stress of Fe-based shape memory alloy

This research explores the impact of thermomechanical treatment on the recovery stress induced by the shape memory effect in an Fe-based shape memory alloy with the composition of Fe-17Mn-5Si-10Cr-4Ni-1(V,C) wt.%. Fe-based shape memory alloys have gained considerable attention for their potential applications in vibration control, energy dissipation, and structural strengthening or re-centering within the construction industry. To evaluate the recovery stress behaviour of this Fe-based shape memory alloy, specimens underwent a two-step aging heat treatment process, involving initial aging at 600 °C for 20 hours, followed by subsequent aging at 680 °C for 8 hours. Then heat-treated samples subjected to a cyclic thermomechanical treatment, involving a combination of deformation up to 2% and heating at 200 °C for 30 min in each cycle. The microstructure and mechanical properties were assessed using techniques such as scanning electron microscopy, as well as tensile tests. The results revealed that the thermomechanical treatment had a notable impact on the microstructure and mechanical properties of the Fe-based shape memory alloy. It resulted in an enhancement of the shape memory effect and recovery stress. These improvements were associated with an increase in the martensitic phase fraction. Additionally, the presence of VC precipitates in the treated samples contributed to the enhancement of the shape memory effect.

Contact Pressure Evolution in Heat-Treated Iron-Based Shape Memory Joints

This paper presents an experimental investigation into the behavior of open-ended Fe-based Shape Memory Alloy (Fe-SMA) tubes under biaxial pre-straining conditions, focusing on development of interface contact pressure as a result of the shape memory effect (SME). During the pre-straining process of Fe-SMA tubes, the cross-section undergoes complete inelastic deformation with a non-uniform distribution. Consequently, non-uniform biaxial pre-strain emerges across the cross-section, leading to the formation of stress-induced martensite in both the radial and circumferential directions. This results in the alteration of the SME due to the direction and interaction of biaxial martensite. Consequently, the material experiences a complex pre-strain state, posing challenges in assessing the SME in Fe-SMA tubes. Nevertheless, it is possible to interpret the complex overall SME performance on the basis of measurements of the resultant pressure exerted by the Fe-SMA tube on a substance, thereby limiting its free recovery. This study explores the development of the interface contact pressure highlighting the impact of heat-treatment on the gripping capacity in Fe-SMA tubes. Via coupling of analytical models with results extracted from an experimental campaign, the resultant pressure at the interface throughout the course of activation is quantified aiding to assess the SME performance. The experimental setup involves Fe-SMA and steel tubes enabling the quantification of interface contact pressure through principal strain measurements at the inner diameter of the steel tube, allowing for differentiation of SME performance under as-received and heat-treated conditions.

Origin of the enhanced pseudo-elasticity of additively manufactured Fe-17Mn-5Si-4Ni-10Cr-(V, C) shape memory alloy fabricated by laser powder bed fusion

This study investigated the origin of the enhanced pseudo-elasticity of additively manufactured vanadium carbide-containing Fe-based shape memory alloys. The aged samples with two different starting microstructures, as-built and solution-treated, showed completely different final microstructures following identical aging treatments. The sample aged directly from the as-built microstructure exhibited typical solidification structures, molten pools, and cellular structures with fine grain sizes inherited from the laser powder bed fusion process with a high cooling rate. In contrast, the sample aged following solution treatment revealed fully recrystallized grain structures with relatively larger grain sizes than the former. Despite having the same type of carbides, the directly aged sample had finer and denser precipitates than the sample aged following solution treatment. Additionally, compared to the sample aged following solution treatment, the directly aged sample exhibited a larger pseudo-elastic recovery strain. The precipitation behavior may have had a negligible impact on the pseudo-elastic behavior because the increase in the pseudo-elastic recovery strain following aging treatment was not significant for either sample. Besides, thermodynamic calculations predicted that the stability of the face-centered cubic (fcc)-γ phase would be increased by local elemental segregation at cell boundaries. Cell boundaries with high fcc-γ phase stability can act as sites that can apply back stress on the deformation-induced hcp-ε phase, thus promoting reverse motion of the Shockley partial dislocations or deformation-induced hcp-ε phase. Furthermore, the smaller grain size enhanced the stability of the fcc-γ phase.

Fe-Mn-Al-Ni Shape Memory Alloy Additively Manufactured via Laser Powder Bed Fusion

Fe-Mn-Al-Ni is an Fe-based shape memory alloy (SMA) featuring higher stability and low temperature dependency of superelasticity stress over a wide range of temperatures. Additive manufacturing (AM) is a promising technique for fabricating Fe-SMA with enhanced properties, which can eliminate the limitations associated with conventional fabrication and allow for the manufacture of complicated shapes with only a single-step fabrication. The current work investigates the densification behavior and fabrication window of an Fe-Mn-Al-Ni SMA using laser powder bed fusion (LPBF). Experimental optimization was performed to identify the optimum processing window parameters in terms of laser power and scanning speed to fabricate Fe-Mn-Al-Ni SMA samples. Laser remelting was also employed to improve the characteristics of Fe-Mn-Al-Ni-fabricated samples. Characterization and testing techniques were carried out to assess the densification behavior of Fe-Mn-Al-Ni to study surface roughness, density, porosity, and hardness. The findings indicated that using a laser power range of 175–200 W combined with a scanning speed of 800 mm/s within the defined processing window parameters can minimize the defects with the material and lead to decreased surface roughness, lower porosity, and higher densification.

Effect of heat treatment on microstructure and pseudoelasticity of a memory‐steel

AbstractThe pseudoelasticity behavior of memory‐steels has recently gained attention for applications in seismic‐resistant structures. The pseudoelasticity can be used to reduce residual deformations in building structures subjected to seismic loading. Fe‐based shape memory alloys (Fe‐SMA), which is also called as memory‐steel, have gained much attention because of their strong shape memory behavior and low material manufacturing cost, which justify their large‐scale application in construction. This research investigated the effects of heat treatment on microstructure and pseudoelasticity of a memory‐steel (Fe‐17Mn‐5Si‐10Cr‐4Ni‐1(V,C) %wt.). Various solution‐annealing treatments from 1000 to 1200 °C for 2 h and aging from 650, 750 and 850 °C were applied to investigate the microstructural evolution and pseudoelasticity behavior of the alloy. The results showed that increasing the solution annealing temperature caused grain growth and pseudoelasticity loss. On the other hand, the precipitation of (Cr,V)Cs after aging resulted in an improved pseudo‐elasticity. The large elastic strain field, which forms near the carbide precipitates, improves the pseudoelasticity. Furthermore, precipitates can provide preferential nucleation sites for the martensite phase and a high density of stacking faults in the austenite matrix. The study concludes that the best pseudoelasticity behavior was achieved after an aging at 750°C for 6 h.

Hybrid Simulation for Evaluation of Seismic Performance of Highway Bridge with Pier Retrofitted Using Fe-SMA Strips

The present research investigates the use of Fe-based shape memory alloy (SMA) strips for seismic retrofitting of rehabilitated RC bridge pier models. Four severely damaged bridge pier models were first rehabilitated by RC jacketing to retrieve at least their lost strength. Three configurations of Fe-SMA strips namely hoop (H), end-anchored (EA), and a combination of previous two approaches (EAH) were adopted. Prestrained Fe-SMA hoops, placed in the plastic hinge region of the bridge pier model, aims at utilizing the recovery stress developed upon thermal activation for application of active confinement pressure on the test specimen. The EA Fe-SMA strips utilize precompression developed in the concrete in the plastic hinge region of the test specimen. The EAH reinforcement scheme was studied for both precompression and active confinement. To compare the seismic performance of the various Fe-SMA retrofitted test specimens with respect to the control specimen, hybrid simulation (pseudodynamic) of an existing highway bridge located in Tripura, India was carried out with the scaled bridge pier test models as experimental elements. Earthquake excitations of different intensity levels were applied in a sequential manner to analyze the behavior of the structure over a damage spectrum ranging from minor cracking to major damage. To determine the ultimate capacity of the test specimens, cyclic tests were carried out after completion of a hybrid simulation. Bridge pier specimens with Fe-SMA in the form of EA reinforcement exhibited enhanced load-carrying capacity but marginal improvement in ultimate displacement while Fe-SMA hoops improved the ultimate displacement of the test specimen with marginal improvement in the peak lateral load. A combination of EA and hoop Fe-SMA reinforcement was found to be more efficient in improving all the seismic performance parameters such as lesser damage and higher load-carrying capacity, stiffness, and energy-dissipation capacity.

Predicting the shear behavior of reinforced concrete beams with Fe-Based shape memory alloy stirrups

Existing studies using Fe-based shape memory alloys (SMAs) for shear reinforcement have focused on strengthening aged structures. Studies on using Fe-SMAs as shear reinforcements for new structures have not been reported. Accordingly, this study performed experiments to evaluate the shear behavior of reinforced concrete (RC) beams with Fe-based SMA stirrups. Ten specimens were prepared for the experiments. The activation of the Fe-SMA stirrup, stirrup spacing, and shear span-to-depth ratio were considered as variables. The Fe-SMA stirrups were activated via electrical resistance heating. Activating the Fe-SMA stirrups applied compressive forces to the specimen, reduced the occurrence of diagonal shear cracks, and improved shear stiffness. However, it did not significantly affect the shear strength. The shear contribution of the Fe-SMA stirrup increased with an increase in the shear span-to-depth ratio and amount of shear reinforcement. In addition, the simulation results using the modified compression field theory (MCFT)-based section analysis model were consistent with the experiment results. Therefore, the model can predict the shear behavior of RC beams with Fe-SMA stirrups.

Shear capacity investigation of RC concrete beams using self-prestressing Fe-based shape memory alloys strips

Shear failure is a sudden and brittle failure, which causes human and economic losses. Hence, enhancement of shear capacity is critical for shear-deficient members of existing structures. In this study, the effectiveness of using Shape Memory Alloy ‘SMA’ strips on the shear capacity of reinforced concrete (RC) beams was investigated in a series of experiments. The experimental work included the study of six RC beams with a 200 × 300 mm cross-section considering shear parameters such as transverse shear reinforcement and the effect of prestressing. Beams were strengthened in U configuration using Fe-SMA strips 30 mm wide and anchored by one expansion anchor (M10-Hilti). The testing was performed in a simply supported condition where each beam was tested twice. The purpose of testing specimens twice was to confirm the results. The activation of the strips was achieved by heating the strips using a custom-made heater up to 200°. The method was proven effective, with an increase in shear capacity of up to 32–45% and 24–25% for specimens strengthened with passive strengthening (non-activated strips) and specimens strengthened by activated SMA strips, respectively. However, the active strengthening improved serviceability conditions by delaying the appearance of cracks and reducing the crack width. The occurrence of the main crack was delayed by 12.5–19.2%, the width of the crack was reduced by more than 65% compared to the reference beam, and the angle of the main crack increased compared to the reference beam as a result of activation. Beams containing internal transverse reinforcement performed better than the beams without shear reinforcement.

Wire and arc additive manufacturing of Fe-based shape memory alloys: Microstructure, mechanical and functional behavior

Shape memory alloys (SMA) are a class of smart materials with inherent shape memory and superelastic characteristics. Unlike other SMAs, iron-based SMAs (Fe-SMA) offer cost-effectiveness, weldability, and robust mechanical strength for the construction industry. Thus, applying these promising materials to advanced manufacturing processes is of considerable industrial and academic relevance. This study aims to present a pioneer application of a Fe–Mn–Si–Cr–Ni–V-C SMA to arc-based directed energy deposition additive manufacturing, namely wire and arc additive manufacturing (WAAM), examining the microstructure evolution and mechanical/functional response. The WAAM-fabricated Fe-SMAs presented negligible porosity and high deposition efficiency. Microstructure characterization encompassing electron microscopy and high energy synchrotron X-ray diffraction revealed that the as-deposited material is primarily composed by γ FCC phase with modest amounts of VC, ε and σ phases. Tensile and cyclic testing highlighted the Fe-SMA's excellent mechanical and functional response. Tensile testing revealed a yield strength and fracture stress of 472 and 821 MPa, respectively, with a fracture strain of 26%. After uniaxial tensile loading to fracture, the γ → ε phase transformation was clearly evidenced with post-mortem synchrotron X-ray diffraction analysis. The cyclic stability during 100 load/unloading cycles was also evaluated, showcasing the potential applicability of the fabricated material for structural applications.

Research Progress and Applications of Fe-Mn-Si-Based Shape Memory Alloys on Reinforcing Steel and Concrete Bridges

In civil engineering, beam structures such as bridges require reinforcement to increase load-bearing capacity and extend service life due to damage, aging, and capacity degradation under long-time services and disasters. The utilization of Fe-based shape memory alloys (Fe-SMA) to reinforce structures has been proven efficient and reliable, and the recovery stress of activated Fe-SMA can satisfy the reinforcement requirements. This article overviews the material characteristics and mechanical properties of Fe-SMA. Furthermore, the principle of thermal activation for reinforcing beams using Fe-SMA is described. On this basis, the joining methods between Fe-SMA members and reinforced components are reviewed, and the existing reinforcement research and applications are analyzed for steel and concrete beams. Finally, given the current shortcomings, this paper puts forward the perspectives that need to be studied to promote Fe-SMA’s reinforcement application in civil engineering.

Electrochemical characterization of a Fe-based shape memory alloy in an alkaline medium and the behaviour in aggressive conditions

A Fe-17Mn-6Si-19Cr-4Ni-1(V,C) shape memory steel (SMS) was characterised electrochemically in its unstrained and pre-strained conditions. The work focused on analysing the passive films generated in alkaline conditions, and on the behaviour of those passive samples in various Cl−/OH− ratios. The passive films were developed by cyclic voltammetry and their characterisation was performed by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS); these tests were also carried out in 304 L stainless steel specimens for comparison purposes. The results indicated that the film characteristics (thickness and composition) were similar in all the samples, although higher corrosion resistance was observed in the 304 L due to the higher Cr content. In addition, the behaviour of the passive samples in aggressive conditions was assessed by potentiodynamic measurements. The results stated that the shape memory steels were more sensitive than the stainless steel to the aggressive conditions, especially when the alloy was pre-strained. It was also observed that the SMS exhibited a characteristic corrosion morphology localized at the grain boundaries.

Electrical discharge machining of Fe-based shape memory alloy: Parametric evaluation with microstructure analysis

In the real world, shape memory alloys (SMAs) are a great option for industrial applications including orthopedic implacers, micro tools, actuators, fitting and screening components, military appliances, aerospace components, biomedical instruments, fabricating essentials, etc. Despite their remarkable characteristics, the effective production of these alloys continues to be a problem for researchers worldwide. This paper has aimed to examine the considered machining responses, that is, material removal rate (MRR) and surface roughness (SR) in electrical discharge or spark machining (EDM) of Fe-based SMA using a Cu-electrode under varying settings of input factors namely as pulse on time (Ton), pulse off time (Toff), peak current (Ip), and gap voltage (GV). The central composite design matrix has been employed for planning the main runs. The experimental results reflect the lowest and highest for MRR as 12.49 and 73.90 mm3/min; and for SR as 5.03 and 6.65 µm, respectively. The microstructure analysis of the EDMed work samples and tool electrode surfaces has also been conducted using scanning electron microscopy. The micrographs exposed the development of debris, craters, micro-cracks, and recast layer creation on the workpiece surface and electrode tool as well. The creation of debris develops as a result of large spark energy at the work sample–tool contact as a result of a high peak current and long pulse on time. Furthermore, single and multi-objective optimization of investigated responses (i.e. MRR and SR) were tried using the desirability approach, teacher learning-based optimization (TLBO), and particle swarm optimization (PSO) techniques. The obtained optimized values for MRR and SR by using the desirability approach, TLBO, and PSO are 62.69 mm3/min and 5.56 µm; 78.85 mm3/min and 4.34 µm; and 78.91 mm3/min and 4.35 µm, correspondingly.

A Review Article on FeMnAlNi Shape Memory Alloy

Shape memory alloys (SMAs) are the materials which remember their original shape once after the deformation has occurred. In recent days, researchers started working on Fe-based shape memory alloys as NiTi shape memory alloys has few drawbacks. Febased shape memory alloys show better advantages over NiTi SMAs. FeMnAlNi SMA has advantage of wide range of operating temperature and low stress dependence. This review article provides information on work carried out on FeMnAlNi SMA which will help the researchers to carry further research work on the alloy for various applications.

Achievements and Perspectives on Fe-Based Shape Memory Alloys for Rehabilitation of Reinforced Concrete Bridges: An Overview.

Reinforced concrete (RC) bridges often face great demands of strengthening or repair during their service life. Fe-based shape memory alloys (Fe-SMAs) as a kind of low-cost smart materials have great potential to enhance civil engineering structures. The stable shape memory effect of Fe-SMAs is generated by, taking Fe-Mn-Si alloys as an example, the martensite transformation of fcc(γ) → hcp(ε) and its reverse transformation which produces considerable recovery stress (400~500 MPa) that can be used as prestress for reinforcement of RC bridges. In this work, the mechanism, techniques, and applications of Fe-SMAs in the reinforcement of RC beams in the past two decades are classified and introduced in detail. Finally, some new perspectives on Fe-SMAs application in civil engineering and their expected evolution are proposed. This paper offers an effective active rehabilitation alternative for the traditional passive strengthening method of RC bridges.