Influence of In Situ and Ex Situ Heat Treatments on the Mechanical Behavior of LPBF-Fabricated Fe–Mn–Al–Ni Shape Memory Alloys

Abstract

This study investigates the fabrication of Fe–Mn–Al–Ni iron-based shape memory alloys (SMAs) using laser powder bed fusion (LPBF) across a range of laser powers. The influence of energy input on material properties was assessed by evaluating the resulting volumetric energy density. Samples were produced under both as-built conditions and subjected to in situ and ex situ treatments to enhance performance. Mechanical properties were characterized through macro-indentation, Profilometry-based Indentation Plastometry (PIP), and nanoindentation techniques, while room-temperature compression testing was conducted to assess superelastic behavior. Microstructural and phase variations were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that increasing the fabrication power improved the mechanical properties of the as-built SMAs, with the optimal performance achieved at 175 W. In situ/ex situ treatments led to a significant reduction in strength but enhanced ductility by up to 39%, along with a 52% reduction in microhardness for samples fabricated at 175 W. Overall, the LPBF-produced Fe–Mn–Al–Ni SMAs exhibited good strain recovery and stability, comparable to those produced by conventional methods. This work demonstrates the potential of LPBF in developing Fe–Mn–Al–Ni SMAs with properties matching traditionally manufactured counterparts.