Innovating 4D-printed microstructures via gas metal arc welding assisted wire-arc additive manufacturing

4D printing refers to the additive manufacturing of a component by incorporating smart materials. The smart materials add the “4th dimension” to 3D-printing by altering the shape/functionality/configuration of the part in response to external stimulus such as heat, stress, pH, electric field, etc. In the current study, shape memory alloy (SMA) plugs were implanted into mild-steel via gas metal arc welding (GMAW) assisted wire-arc additive manufacturing (WAAM). The NiTi SMA powder was employed as secondary addition within the printed layers, while the FeMnSi based alloy evolved in-situ during the 4D-printing process. Significant elemental heterogeneity was found in the Fe-Mn-Si based SMA plugs containing Ni[sbnd]Fe rich solidified droplets, owing to the composition of the wire used for deposition. The Ni[sbnd]Fe rich phases depicted the substitution of Ti by Fe in the NiTi pre-cursors. The large SMA plugs incorporated into the printed mild steel depicted the formation of a macro composite structure. The presented results are expected to considerably reduce the cost of SMA application through the printing of novel monolithic SMA-steel composites using wires and SMA powders as raw materials.