Modulating Heat Input to Optimize Corrosion Resistance of Nickel–Aluminum Bronze Manufactured by Cold Metal Transfer Additive Manufacturing

The influence of heat input (HI) on the microstructure, microhardness, electrochemical corrosion performance of cold metal transfer additively manufactured (CMTAM) nickel-aluminum bronze alloys was investigated. The nickel-aluminum bronze exhibited an α-Cu austenite matrix with minor γ₂-Cu₉Al₄ and κ phases. As HI increased, the microstructure coarsened progressively. Electron backscatter diffraction (EBSD) analysis revealed that with increasing HI, the grain size gradually increased and the Schmid factor increased. Consequently, the microhardness declined from 198.3 HV to 171.7 HV. The decrease in microhardness with increasing heat input is primarily attributed to the grain coarsening and the coarsening and uneven distribution of the κ phase. As the heat input (HI) increased from 243.8 J/mm to 644.7 J/mm, the corrosion current density rose significantly from 2.56 ± 0.04 μA/cm² to 7.52 ± 0.07 μA/cm². This result indicates a marked deterioration in the material's corrosion resistance. This phenomenon can be attributed to the grain coarsening and the distribution of Al solute within the microstructure. The CMTAM nickel-aluminum bronze alloys hold significant potential for enhancing the reliability and long-term protection of marine engineering equipment.