Parametric Study on Investigations of GMAW-Based WAAM Process Parameters and Effect on Microstructure and Mechanical Properties of NiTi SMA

In the present study, an attempt was made to build a thin-walled structure consisting of 10 layers using nitinol wire on a titanium substrate via a gas–metal arc welding (GMAW)-based wire-arc additive manufacturing (WAAM) process. A thin-walled structure was fabricated by using nitinol wire on a titanium substrate at the optimized parameters of a wire feed speed of 6 m/min, a travel speed of 12 mm/s, and a voltage of 20 V. In a microstructural study, the heat-affected zone was observed to have coarse grains and be columnar in shape, and the first layer exhibited a mix of dendritic structures. The mid-layers demonstrated a mix of coarse and fine columnar grains with dendritic colonies, while the last few layers demonstrated fairly equiaxed grains as well as a finer microstructure, as the cooling rates were very slow. The ultimate tensile strengths (UTSs) obtained at the bottom and top portions were found to be 536.22 MPa and 586.31 MPa. Elongation (EL) degrees of 10.72% and 11.57% were observed in the bottom and top portions, respectively. The fractography of the tensile specimen showed good toughness and ductility of the fabricated nitinol specimen. A microhardness examination showed a minimum value of 236.56 HV in the bottom layer and a maximum value of 316.78 HV in the topmost layer.