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In the present work, CMT-based robotic MIG welding is carried out for wire arc additive manufacturing of SS308L part. Commercially available SS308L-T1 wire is used as feedstock material. Studies of direction-specific microstructure evolution and mechanical property characterization of as-built specimens are carried out. WAAMed SS308L exhibits a typical microstructure consisting of grain boundary δ ferrite with varied morphologies (vermicular/skeletal and lathy) within γ austenite dendrites. The amount of δ ferrite along with its morphology is observed to be varied from location to location, within the as-deposited specimen. Such variation diminishes after the heat treatment. The average ultimate tensile strength of horizontally cut specimens supersedes than that of vertically cut specimens. Heat treatment causes reduction in microhardness value of WAAMed SS308L. Additionally, temperature data as recorded by the thermocouple (tacked with the substrate plate) are utilized to understand various heat interaction phenomena during the WAAM process. Effect of post-deposition heat treatment is also studied. [ABSTRACT FROM AUTHOR]

A slab of dimension (152 × 25 × 18) mm3 is successfully fabricated through Cold Metal Transfer + Metal Inert Gas-based Wire Arc Additive Manufacturing (WAAM). 4.3 kg/h deposition rate is achieved. WAAMed Inconel 718 exhibits dendritic microstructure which grows along the build direction. In the solid solution matrix of Ni–Cr–Fe, Laves phase, Nb-rich MC-type carbides and delta (δ ) phases are detected. The average tensile strength along horizontal direction is obtained as ~ 824 MPa. Location-specific microstructure evolution causes significant extent of property anisotropy predominantly along the build direction. The horizontal tensile specimen extracted from the bottom region of the slab exhibits the highest tensile strength (UTS), while the lowest tensile strength is obtained for the specimen extracted from the middle zone of the fabricated slab. Temperature data as recorded by the thermocouples are utilized to understand the complex heat interaction phenomena during WAAM process. Laves phase is completely dissolved during homogenization treatment thus microstructure of aged specimen only consists of strengthening phase, i.e., γ ″ (Ni3Nb) and Nb-rich MC carbides. [ABSTRACT FROM AUTHOR]

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]

Mechanical and corrosion properties of welded duplex stainless steel (DSS) structures are of paramount consideration in many engineering applications. The current research investigates the mechanical properties and corrosion integrity of duplex stainless-steel weldment in a simulated 3.5% NaCl environment using specially developed novel electrodes without the addition of alloying elements to the flux samples. Two different types of fluxes having basicity indexes of 2.40 and 0.40 were used to coat E1 and E2 electrodes respectively for DSS plate welding. The thermal stability of the formulated flux was evaluated using thermogravimetric analysis. The chemical composition, using optical emission spectroscopy, and the mechanical and corrosion properties of the welded joints were evaluated as per different ASTM standards. X-ray diffraction was used to find out the phases present in the DSS welded joints while a scanning electron equipped with EDS was used for microstructural examination of the weldments. The ultimate tensile strength of welded joints made using the E1 electrode was in the range of 715–732 MPa and that of the E2 electrode was found to be 606–687 MPa. The hardness was increased with increased welding current from 90 to 110 A. The welded joint with E1 electrode coated with basic flux has better mechanical properties. The steel structure in 3.5% NaCl environment possesses substantial resistance to corrosion attack. This validates the performance of the welded joints made by the newly developed electrode. The results are discussed on the basis of the depletion of alloying elements such as Cr and Mo observed from the weldments with the coated electrodes E1 and E2 as well as precipitation of the Cr2N in the welded joints made by E1 and E2 electrodes. [ABSTRACT FROM AUTHOR]