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 NiFe rich solidified droplets, owing to the composition of the wire used for deposition. The NiFe 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.