FeMnNiAl Iron-Based Shape Memory Alloy: Promises and Challenges

Abstract

Among all shape memory alloys, the iron-based FeMnNiAl has emerged as one of the most promising compositions with a huge superelasticity temperature window (> 400 °C). In this article, we first point to the high local transformation strains (> 10%) and high transformation stress levels (500–700 MPa) that result in a large work output. When subjected to either tensile or compressive loading, the transformation stress exhibits very small temperature dependence (Clausius–Clapeyron slope less than 0.2 MPa/°C in compression and 0.5 MPa/°C in tension) and an extremely small adiabatic temperature rise (less than 1 °C) during transformation. The complexity in transformation behavior associated with the presence of grain boundaries (GBs) is discussed. In particular, the work provides insight in the localization occurring at GBs due to transformation front–GB interactions and the potential cracking that can degrade fatigue performance. Overall, this work provides a deeper insight into the deformation response, advantages, and drawbacks of FeMnNiAl SMA. The comprehensive handling of various aspects of this alloy system paves the way for the development of future iron-based shape memory alloys.