Dislocations mobility in superalloy-steel hybrid components produced using wire arc additive manufacturing

A hybrid component consisting of Inconel 718 superalloy (IN718) and mild/low structural steel (grade S275) was fabricated using the wire + arc additive manufacturing (WAAM) technology to evaluate the feasibility, texture, and the corresponding characteristics. S275 is considered as a mild/low alloy steel that is compatible with IN718 and can serve as a mechanically under-matched substrate for WAAM deposition with potential use in the petrochemical industry. Characterization of the interfacial hybrid part was conducted through Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Electron Backscatter Diffraction (EBSD) in three different states of as-built (AB), solution-treated (ST), and aged (STA) conditions. EDS elemental mapping confirmed the presence of Laves closer to the interface even after 1-hour solutionizing at 1080 °C. Solution-treatment resulted in eliminating microsegregation (mainly Nb) and considerable Laves dissolution, along with a significant decrease of the hardness in both WAAM-deposited IN718 and the substrate. The bulk texture of WAAM-deposited IN718 was measured by neutron diffraction in all three states of AB, ST, and STA, showing a strong 〈0 0 2〉 texture parallel to the building direction (BD). Elastic-field mathematical models were used to interpret the role of heat treatment in perfect-, and partial dislocations’ mobility and Peierls-Nabarro stress by considering the neutron diffraction and nanohardness data collected across the interface. Limiting aspects associated with dissimilar joining of IN718 and S275 alongside post-processing heat-treatments were pointed. Recommendations were made to facilitate possible additive repair of IN718 hybrid parts for various industrial applications.