Wire-arc additive manufactured nickel aluminum bronze with enhanced mechanical properties using heat treatments cycles

Abstract

Wire-arc additive manufacturing (WAAM) technique was used to develop nickel aluminum bronze (NAB) components for naval applications. The microstructural changes were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS). As-built WAAM-NAB consists of κII (globular Fe3Al) and κIII (lamellar NiAl) phases in the interdendritic regions and fine Fe-rich κIV particles in the Cu-matrix. Along the build direction, the WAAM-NAB flat samples exhibited yield and ultimate tensile strength values of 380 and 708 MPa, respectively, and 34 % elongation. Furthermore, three different heat-treatments were performed on the samples in a view to evaluating their effect on mechanical properties. When heat-treated to 350 °C for 2 h (HT-1), there are no significant microstructural changes, and tensile properties along the build direction are similar to the as-built WAAM-NAB. Heat-treatment at 550 °C for 4 h (HT-2) produced a new needle-like κv phase in the α-matrix, coarsening of globular κII, partial spheroidization of lamellar κIII, and reduced amount of κIV precipitation. As compared to the WAAM-NAB, HT-2 samples exhibited a significant increase in yield strength (∼90 MPa), and ultimate tensile strength (∼60 MPa); however, tensile ductility was observed to drop by 20 %. After heat-treatment at 675 °C for 6 h (HT-3), globular κII and needle-like κv were coarsened, lamellar κIII was completely spheroidized, and the amount of κIV was significantly reduced. HT-3 samples showed better tensile strength (∼37 MPa) than the WAAM-NAB with marginal loss (6%) in the ductility.