# Densification Behavior and Microstructure of Nickel Aluminum Bronze Alloy Fabricated by Laser Powder Bed Fusion

## TL;DR

This paper studies how laser powder bed fusion affects the structure and strength of a bronze alloy used in marine applications.

## Contribution

The study reveals unique microstructural changes and mechanical improvements in NAB alloy fabricated via L-PBF compared to traditional casting.

## Key findings

- As-built L-PBF NAB samples have columnar β′ grains with α and κ phases, differing from cast microstructures.
- Annealing transforms the L-PBF microstructure into a dendritic morphology and increases mechanical properties significantly.
- L-PBF NAB shows higher yield strength, tensile strength, and microhardness than cast NAB due to rapid solidification.

## Abstract

Nickel–Aluminum–Bronze (NAB) has gained significant attention in marine applications due to its excellent corrosion resistance and has shown growing potential for laser powder bed fusion (L-PBF) additive manufacturing. However, research on the fabrication of NAB alloys using L-PBF remains relatively limited. In this study, fully dense NAB samples were successfully fabricated through L-PBF process parameter optimization. The microstructural evolution and mechanical properties of both as-built and annealed L-PBF samples were systematically investigated and compared with those of traditionally cast NAB. The results reveal that the as-built L-PBF specimens primarily consist of columnar β′ grains, with the α phase distributed along the grain boundaries and a small amount of κ phase precipitated within the β′ matrix, distinctly different from the cast microstructure characterized by a columnar α-phase matrix with precipitated β′ and κ phases. After annealing at 675 °C for 6 h, the β′ phase in both methods decomposed into α + κ phases, and the original columnar structure in the L-PBF specimens transformed into a dendritic morphology. Compared to the cast samples, the L-PBF-produced NAB alloy exhibited significantly enhanced yield strength, tensile strength, and microhardness, attributable to rapid solidification during the L-PBF process. Following annealing, the yield strength and elongation increased by 12.8% and 184.4%, respectively, compared to the as-built condition, resulting from the decomposition of the martensitic phase into α + κ phases and further grain refinement.