Effect of bidirectional and switchback deposition strategies on microstructure and mechanical properties of wire arc additive manufactured Inconel 625.

The switchback deposition strategy is a unique approach where the torch is moving cyclically forward and backward for preventing the unidirectional grain growth in wire + arc additive manufacturing (WAAM). Experiments were conducted for comparing the walls deposited in bidirectional and switchback strategies. The travel speed, inert gas flow rate, and number of deposited layers were kept constant for both the conditions. The grain growth behavior was identified from the bottom to top and welding direction. Finally, samples were extracted from the walls for mechanical property analysis and microstructural studies. Switchback mode produces ~ 70% γ′-phase whereas the bidirectional mode has ~ 77% γ′-phase in the matrix. Inconel 625 sample deposited using switchback technique revealed ~ 10-µm lesser primary dendritic spacing in the middle region and the standard deviation of overall structure is ~ 5 µm less compared with bidirectional deposition resulting in relatively higher average hardness. The switchback mode also results in ~ 2 µm lesser average secondary dendrite size among both the deposition strategies. The switchback deposition mode displayed a higher average yield strength (σ_y) (~ 440 MPa) than the bidirectional mode (~ 390 MPa) and approximately identical ultimate tensile strength (σ_u) with a 20-MPa variation. [ABSTRACT FROM AUTHOR]