Microstructural and interfacial characteristics in repair of nickel-aluminum bronze by in-situ synthesis of Cu-Al alloys via directed energy deposition

Abstract

Directed energy deposition (DED) has demonstrated significant potential for component repair, owing to its flexibility in deposition path and powder feedstock selection. However, research on manufacturing Cu-Al alloys via DED remains limited. This study employed a pre-mixed blend of CuNi2SiCr and Al-Mg-0.7Si powders to synthesize Cu-Al alloys in situ for the DED-based repair of nickel-aluminum bronze (NAB). By varying the mass fraction of the Al-Mg-0.7Si powder (6, 8, 10, and 12 wt%), the effects of aluminum content on the microstructure, hardness, and tensile behavior of the repaired samples were investigated by micro- and nanoscale characterization. The results indicated that all repaired samples were free of obvious defects, such as pores or thermal cracks, and exhibited excellent metallurgical bonding between the repaired area and substrate. The microstructures of samples containing 6 and 8 wt% Al-Mg-0.7Si powder were predominantly α phase while those with 10 and 12 wt% Al exhibited β₁ martensitic twin structures. The samples repaired with 6 wt% Al-Mg-0.7Si powder demonstrated the best tensile properties, with a tensile strength of 624 MPa and elongation of 14.4 %. The tensile properties of the 10 and 12 wt% Al samples were lower owing to the precipitation of the Widmanstätten α phase at the β₁ martensitic grain boundaries. Fracture locations varied across samples, but cracks did not propagate along the repaired interface, suggesting excellent interfacial bonding strength. Additionally, unusual γ₂ phase precipitates were observed in all the samples. This research provides valuable insights into the feasibility of in-situ Cu-Al alloy fabrication via DED for the repair of NAB.