Microstructural evolution and mechanical behavior of nickel aluminum bronze Cu-9Al-4Fe-4Ni-1Mn fabricated through wire-arc additive manufacturing

Abstract

As a step forward toward the development of the next generation of nickel aluminum bronze (NAB) components using wire-arc additive manufacturing (WAAM), square bars were printed in the vertical direction. The as-built microstructure was characterized using multi-scale electron microscopy techniques, where the differences in phase formation were compared to the reference cast-NAB based on the solidification characteristics. The as-cast microstructure typically consists of Cu-rich α-matrix, and four types of intermetallic particles referred to as κ-phases. In the WAAM-NAB, the formation of κI was suppressed due to high cooling rates. The microstructure was finer and the volume fraction of intermetallic particles was significantly lower than that of the cast-NAB. Based on energy dispersive spectroscopy (EDS) technique and diffraction pattern analysis using transmission electron microscopy (TEM), the phases formed in the interdendritic regions were identified as κII (globular Fe3Al) and κIII (lamellar NiAl), whereas numerous fine (5–10 nm) Fe-rich κIV particles were precipitated uniformly within the α-matrix. Electron backscatter diffraction analysis revealed weak texture on both parallel and perpendicular planes to the building direction with (100) poles rotated away from the build direction. The WAAM-NAB sample exhibited considerably higher yield strength (˜88 MPa) and elongation (˜10%) than the cast-NAB, but the gain in the ultimate tensile strength was marginal.