Microstructural investigation of graphene reinforced nickel aluminum bronze prepared via laser powder bed fusion

Nickel aluminum bronze (NAB) powders coated with reduced graphene oxide (RGO) were successfully fabricated using additive manufacturing (AM) via laser powder bed fusion. The resulting samples were characterized using a suite of complementary techniques, including x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, nanoindentation, x-ray computed tomography, and electron backscatter diffraction. These methods were employed to reveal the micro- and nanoscale features within the fine dendritic microstructure. The as-fabricated microstructures were observed to deviate significantly from typical as-cast configurations. In the AM RGO-coated NAB specimens, the formation of the κI phase was notably suppressed and is attributed to the rapid cooling rates inherent to the AM process. Comparatively, the AM RGO-coated NAB samples exhibited a more refined microstructure with a significantly reduced volume fraction of intermetallic particles compared to their cast NAB and uncoated AM-NAB counterparts. Mechanical assessment through nanoindentation revealed that the RGO-coated parts possess a higher modulus and hardness relative to cast NAB, with an enhancement of over 30%. These enhancements in mechanical properties are attributed to the microstructural advantages conferred by AM processes, including diminished segregation, uniform precipitation distribution, and reduced grain size.