Experimental investigation on microstructure and mechanical property of wire arc additively manufactured SS308L built part.

Wire arc additive manufacturing (WAAM) is a class of arc-based metal additive manufacturing (AM) under the category of direct energy deposition. As compared to other metal-based AM techniques, WAAM is capable of fabricating medium-to-large sized part (having low level of design complexity) with near fully-dense structure. Ease of near-net shaping with high material utilization rate has made the process economic in various industrial applications staring from prototype to customized product fabrication. Quality of the built part is strongly affected by the feedstock wire composition, welding parameters and deposition strategy. Due to complicated thermal history, WAAMed part suffers from considerable anisotropy in microstructure as well as mechanical properties. The present work attempts to fabricate a 3D slab by layer-wise deposition of molten SS308L-T1 feedstock wire through CMT + MIG based WAAM process. Initially, a few pilot experiments (by depositing single track bead-on-plate welds and stacked weld specimens) are performed to determine values of the appropriate process parameters for WAAM of SS308L part. The appropriate setting of parameters which includes current, voltage, gas flow rate, nozzle-to-plate distance, start/end current percentage, degree of overlap and deposition strategy (applicable for stacked specimens), etc. are obtained based on visual inspection of the built quality and measurable features of bead geometry. Finally, a 3D wall is successfully fabricated having approximate dimension 150 × 25 × 30 mm3. The microstructure evolution and mechanical property characterization of the as built part are carried out. It is experienced that microstructure and mechanical property of WAAMed SS308L are location-dependent. The as built microstructure contains δ ferrite (skeletal, vermicular and lathy morphologies) which is deposited at grain boundaries of γ austenite. The middle zone of the fabricated slab appears to be relatively softer than top and bottom zones; middle zone corresponds to the lowest tensile strength along horizontal direction (~ 541 MPa) but the highest fracture strain (elongation percent ~ 38%). The average tensile strength along horizontal direction is obtained as ~ 548 MPa. Fractographic results of failed tensile specimens evidence ductile fracture mode characterized by dimples along with the presence of second-phase spherical particles. The average microhardness of the as built SS308L obtained is 171 HV0.1. [ABSTRACT FROM AUTHOR]