Effect of microstructure on the shape memory effect of Fe-17Mn-10Cr-4Ni (wt.%) alloy fabricated by L-DED

Fe-based shape memory alloys (SMA) are gaining attention as a potential low-cost alternative to Ni-Ti alloys, particularly for applications in construction and actuation systems. In Fe-based SMAs, shape memory effect (SME) is significantly influenced by microstructural features, including dislocations, precipitates, and grain morphology and texture. Unique microstructural features inherited from laser direct energy deposition (L-DED) process may have the potential to enhance the SME of the Fe-based SMA. In this study, microstructure and shape memory properties of Fe-17Mn-10Cr-5Si-4Ni (wt.%) fabricated by the L-DED process were investigated Fe-17Mn-10Cr-5Si-4Ni (wt.%) SMA produced by L-DED under various volumetric energy density (VED) conditions were investigated. SME of Fe-based SMAs is known to be based on the γ-FCC to ε-HCP phase transformation. However, rapid-solidification rate of L-DED process may lead to the formation of the δ-BCC phase, which does not involve on the γ-FCC to ε-HCP phase transformation. To suppress the formation of undesired δ-BCC phases, phase fractions of the alloy produced under different VED conditions were analyzed. Tensile and bending tests for evaluating mechanical properties and SME were conducted along both L-DED building and scanning directions aiming to examine anisotropic mechanical properties and the SME. It was found that the solidification cell structures occurred by the rapid-solidification rate of the L-Ded could significantly enhance the SME, probably because the cell boundaries could act as back-stress sites that could enhance the reverse phase transformation from ε-HCP to γ-FCC.