Impacts of post-printing heat treatment on the microstructure and mechanical properties of wire-arc additively manufactured nickel aluminum bronze alloy

Abstract

Wire-arc additive manufacturing (WAAM) is an effective process for producing and repairing large-scale Nickel Aluminum Bronze (NAB) components, particularly within the marine defense and aerospace industries. This study investigates the impact of two post-printing heat treatments —direct aging and solutionizing followed by aging—on the microstructure and mechanical properties of WAAM-NAB alloy. The as-printed WAAM-NAB alloy (As-PNAB) shows a complex microstructure with large globular κ_II (Fe₃Al) and lamellar κ_III (NiAl) phases. Direct aging at 675 °C for 6 h (DA-NAB) and solutionizing at 950 °C for 2 h before aging (SA-NAB) result in a more uniform κ-phases distribution and the formation of needle-like κ_IV phases. DA-NAB yields smaller precipitates, while SA-NAB achieves a more homogenous microstructure with larger precipitates that remain smaller than those in As-PNAB. DA-NAB displays superior mechanical properties, with enhanced yield strength, ultimate tensile strength, and ductility compared to SA-NAB. DA-NAB was characterized by a more uniform grain structure with reduced dislocation density, contributing to its improved mechanical performance. Direct aging was identified as the most effective heat treatment for achieving a favorable balance of strength and ductility, outperforming the solutionizing and aging approach.