Effect of Pre-straining, Activation Temperature and Thermomechanical Training on Recovery Behavior of Femnsi Based Sma

Iron-based shape memory alloys (Fe-SMAs) can be used for strengthening of existing concrete structures in civil and architectural engineering. This study investigates the recovery behavior of Fe-SMAs under varying pre-strain levels, activation temperatures, and thermos-mechanical training conditions. An FeMnSi-based alloy (Fe-17Mn-10Cr-5Si-4Ni-0.2C-0.8V wt.%) underwent two-step aging, followed by pre-straining at 2 %, 4 %, and 8 % and activation at 200 degrees C, 400 degrees C, and 600 degrees C. Recovery stresses under rigid restraint reached 500 MPa, 490 MPa, and 440 MPa at 200 degrees C for 2 %, 4 %, and 8 % pre-strain, respectively, while at 8 % pre-strain and 600 degrees C, recovery stress exceeded 600 MPa. Free-recovery strains for 8 % pre-strain were 1 %, 2 %, and 2.15 % at 200 degrees C, 400 degrees C, and 600 degrees C, respectively. Thermomechanical training involving 10 cycles of 3 % pre-strain and annealing at 400 degrees C and 600 degrees C increased the shape recovery ratio to 95 %. Microstructural analysis showed reduced twin boundary density, enhancing the epsilon-martensite to gamma-austenite transformation and improving recovery performance after training. Optimal pre-strain levels, activation temperatures, heat treatment, and thermomechanical training significantly improved the shape memory effect (SME) and super elasticity (SE) of Fe-SMAs. Key findings demonstrate that: (1) activation at 350 degrees C-600 degrees C maximized recovery stress and strain, with diminishing returns at excessively high temperatures; (2) thermomechanical training enhanced SME and SE via work hardening and increased dislocation density; and (3) microstructural refinement through annealing improved recovery ratios, with optimal performance achieved at 600 degrees C. These results provide valuable insights into tailoring the recovery behavior of Fe-SMAs for advanced applications.