Effect of Boron Addition on a Fe-based Shape Memory Alloy

Shape memory alloys (SMAs) are a unique class of functional materials that possess pseudoelasticity, where their original shape can be recovered after loading through a reversible, diffusionless, martensitic transformation. SMAs are widely manufactured and used in many disciplines such as medical, aerospace, and civil engineering. The three most common types of SMAs are NiTi-based, Cu-based, and Fe-based SMAs. NiTi-based SMAs are the most widely utilized due to their excellent pseudoelasticity, biocompatibility, and high recoverable strain. Fe-based SMAs offer a promising alternative, while also exhibiting a minimal temperature dependence on critical stress, thus maintaining stable pseudoelastic properties across a wide temperature range. Fe-based SMAs typically suffer from early failure during cycling due to grain boundary triple junctions. One solution to address this issue is to create an ultrafine-grained material. Boron, even in very small amounts, has been shown to act as a grain refiner in Fe-based SMAs, while also improving pseudoelasticity.

In this study, we compared the microstructure and performance of an (Fe_43.5Mn₃₄Al₁₅Ni_7.5)_.95B_0.05 SMA with Fe_43.5Mn₃₄Al₁₅Ni_7.5 SMA. Both alloys were characterized using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) to analyze the microstructure and elemental composition, respectively. Additionally, compression testing was performed to compare the pseudoelastic response and X-ray diffraction (XRD) was used for phase analysis.