Bead overlapping under oscillatory mode during wire-arc directed energy deposition of superalloy: Investigation on microstructure and mechanical properties

Understanding the multi-bead overlapping process in wire-arc directed energy deposition (DED) is critical for the process and performance control of large superalloy components. In this work, a comprehensive analysis of the evolution of microstructure and mechanical properties of wire-arc DED of multi-bead Inconel 718 structure with oscillatory deposition mode was carried out. The correlation between deposition characteristics, thermal history, microstructure, and properties was established. The results indicate that multi-bead, as compared to single-bead, leads to coarser dendrites, frequent cracks, and pore defects in the overlap area by altering the thermal cycling in their vicinity. Meanwhile, the shape of the Laves phase here was transformed from small-sized islands to large-sized long chains, and the overlap area still retains Laves phases of reduced size after heat treatment. This ultimately results in inhomogeneity in the mechanical properties of the deposited wall structure, severe reduction (∼78.9 %) of the tensile ductility, and a slight reduction (∼5 %) of the strength in the overlapping area. The fracture mechanism changes from ductile fracture to cleavage fracture in the overlap area. However, the superalloy deposited by the oscillation mode still maintains its high strength advantage, with a minimum yield strength of 1126 MPa. This study provides new insights for the optimization of the wire-arc DED process for large components of Inconel 718 superalloys and offers new insights into high-performance additive manufacturing of nickel-based superalloys.