Microstructure, texture and mechanical performance of a nickel–aluminium bronze / martensitic stainless steel bimetal produced by direct energy deposition

Abstract

This study investigates the microstructural evolution, crystallographic texture, and mechanical properties of a nickel-aluminium bronze (NAB)/410 NiMo martensitic stainless steel bimetallic structure fabricated via wire arc additive manufacturing (WAAM). The work provides a detailed assessment of the interfacial characteristics, phase transformations, and texture development across both alloys, as well as their impact on mechanical behaviour. Microstructural characterisation using optical microscopy, SEM, EBSD, and TEM revealed that the stainless steel region predominantly consists of martensite with minor fractions of δ-ferrite, α-ferrite, and retained austenite. A distinct Fe-rich interfacial layer was identified, from which columnar dendrites grow epitaxially into the NAB side. The NAB region exhibits α-phase grains with various k-phase precipitates whose distribution and morphology evolve with build height due to thermal cycling and dilution effects. Evidence of liquid metal embrittlement (LME) was observed at the interface. Texture analysis indicated a weak crystallographic texture in the stainless steel due to solid-state transformations, whereas the NAB exhibited a more textured structure, especially <101>//BD. Despite the presence of LME cracks at the interface, tensile testing consistently resulted in fracture within the NAB region, away from the interface, demonstrating effective load transfer across the interface under uniaxial tensile loading parallel to the building direction. The bimetallic structure achieved an ultimate tensile strength of 587 MPa and total elongation of ∼12%.