Strain-Rate-Dependent Thermo-Microstructural Evolution in Fe-Mn-Si Shape Memory Alloys Under Cyclic Tensile Training...

Area of Science:

• Materials Science
• Metallurgy
• Solid Mechanics

Background:

• Iron-based shape memory alloys (Fe-SMAs) offer cost-effective, corrosion-resistant solutions for structural retrofitting.
• The influence of strain rate on the cyclic training behavior of Fe-SMAs requires further investigation.

Purpose of the Study:

• To investigate the effect of quasi-static versus impact strain rates on the thermo-microstructural evolution of Fe-SMAs during cyclic tensile training.
• To understand how strain rate influences transformation temperatures, enthalpies, and microstructural characteristics.

Main Methods:

• Cyclic tensile training at quasi-static and impact strain rates.
• Differential Scanning Calorimetry (DSC) to measure transformation temperatures and enthalpies.
• Electron Backscatter Diffraction (EBSD) to analyze phase fractions, lattice distortion, and variant statistics.

Main Results:

• Impact loading resulted in a more rapid increase in transformation enthalpy and a more pronounced decrease in thermodynamic driving force compared to quasi-static loading.
• Higher strain rates led to faster accumulation of internal stress and dislocation storage, lowering the effective stress for martensitic transformation.
• EBSD analysis showed increased lattice distortion and a higher proportion of single-variant martensite in impact-trained samples, facilitating transformation and enhancing shape recovery.

Conclusions:

• Strain rate significantly impacts the coupled thermo-microstructural evolution in Fe-SMAs during cyclic training.
• High strain rates accelerate thermodynamic changes and microstructural evolution, leading to improved shape recovery.
• Understanding these rate-dependent effects is crucial for optimizing Fe-SMAs in applications like structural retrofitting.