Microstructural evolution in wire-fed electron-beam directed energy deposition Ni-Al bronze and its implications for mechanical properties and corrosion behavior

Abstract

Nickel–aluminum bronze (NAB) alloys are widely employed in marine engineering owing to their excellent corrosion resistance and mechanical properties. Electron beam directed energy deposition (EB-DED), a wire-fed additive manufacturing technique, was employed to fabricate high-performance NAB alloys. However, its intrinsic layer-by-layer deposition process tends to induce microstructural gradients, thereby compromising the uniformity of material properties. This work systematically investigates the influence of build height on the microstructure, mechanical properties, and corrosion behavior of an EB-DED fabricated NAB alloy. The results reveal the following: (1) The synergistic effect of cyclic thermal input and heat accumulation leads to a gradient microstructure. In the middle and bottom regions, cyclic thermal input decomposes the β′ phase into α and κ phases, while rapid cooling in the bottom region results in a refined α+κ microstructure with uniformly distributed κ phases. In contrast, heat accumulation in the middle and upper regions causes microstructural coarsening. (2) The bottom region exhibits optimal mechanical properties, with a yield strength of 394.11 MPa, ultimate tensile strength of 786.59 MPa, and elongation of 32.87 %, attributed to grain refinement, κ-phase dispersion strengthening, and the absence of the brittle β′ phase. (3) Corrosion resistance varies significantly with build height. The upper region, containing the β′ phase, shows the poorest corrosion resistance due to preferential dissolution of the β′ phase. The bottom region demonstrates superior corrosion resistance, owing to the absence of the β′ phase, a refined microstructure, uniform elemental distribution, and rapid depletion of fine κ phases, which promote the formation of a stable passive film and mitigate galvanic corrosion. This work elucidates the build height-microstructure-property relationship in EB-DED fabricated NAB alloy, providing a theoretical foundation for optimizing thermal management strategies and developing high-performance homogeneous NAB components, which is crucial for enhancing the reliability of critical parts under harsh operating conditions.