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

Abstract

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 parts (having a low level of design complexity) with a nearly fully dense structure. Ease of near-net shaping with a high material utilization rate has made the process economic in various industrial applications starting from prototype to customized product fabrication. The quality of the built part is strongly affected by the feedstock wire composition, welding parameters, and deposition strategy. Due to its complicated thermal history, the 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 a 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 the WAAM of the 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 dimensions 150 x 25 x 30 mm(3). The microstructure evolution and mechanical property characterization of the as-built part are carried out. It is experienced that the microstructure and mechanical properties of WAAMed SS308L are location-dependent. The as-built microstructure contains d ferrite (skeletal, vermicular, and lathy morphologies) which is deposited at grain boundaries of? austenite. The middle zone of the fabricated slab appears to be relatively softer than the top and bottom zones; the middle zone corresponds to the lowest tensile strength along the horizontal direction (similar to 541 MPa) but the highest fracture strain (elongation percent similar to 38%). The average tensile strength along the horizontal direction is obtained as similar to 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.