Effect of low-level Ti microalloying on the microstructure, mechanical properties, and corrosion behaviour of WAAM-processed nickel-aluminium bronze

The coarse columnar grains and anisotropic mechanical properties inherent to wire arc additive manufacturing (WAAM) significantly limit the performance of nickel-aluminum bronze (NAB) alloy. To address this, the effects of Ti nanoparticles on WAAM-NAB alloy are systematically investigated. Results reveal a non-monotonic relationship between Ti content and grain refinement. When 0.03 wt.% Ti is added, the insufficient nucleation sites lead to grains coarsening (75.2 μm) and a high proportion of columnar grains, exacerbating microstructural heterogeneity and mechanical anisotropy. However, the solid solution of Ti atoms in the α matrix induces lattice deformation and increases the hardness. In contrast, additions of 0.05 wt.% and 0.1 wt.% Ti effectively promote heterogeneous nucleation, resulting in significant grain refinement (17.3 μm/21.6 μm). The increase in grain boundary density enhances strength and hardness by hindering the movement of dislocations. Notably, the weakening of texture strength and the optimized morphology of the κ Ⅲ phase in 0.1 wt.% Ti-modified alloy further enhance the microstructural homogeneity, enabling it to exhibit the optimal comprehensive mechanical properties. Compared with the deposited alloy, the synergistic effect of grain refinement and enhanced homogeneity endowed the 0.1 wt.% Ti-modified alloy with superior corrosion resistance, as evidenced by a 15.6% reduction in corrosion current density and a positive shift of 4.34 mV in corrosion potential. This work demonstrates that Ti microalloying is an effective approach for achieving simultaneous enhancement in both mechanical and corrosion properties of WAAM-NAB alloy.