Investigating the Influence of Al Contents on Microstructure and Mechanical Properties of Ni₃Al Superalloy Fabricated by Twin Wire-Based Direct Arc Energy Deposition

In situ synthesis of Ni3Al by simultaneously feeding both Ni and Al wires into the molten pool is a common wire-based additive manufacturing technology for Ni3Al superalloys. However, Ni3Al superalloys within a composition gap still have not yet been synthesized. The optimal composition range has also not been investigated yet. Herein, Ni3Al superalloys with Al equivalents between 17 and 25 at.% are fabricated by twin wire-based direct arc energy deposition by adjusting the relative feeding speed. Microstructural analysis shows that the solidification products generate no gamma ' precipitation when Al content is 17 at.%. Al promotes the formation of gamma ' phase, as the Al content increases, the deposited Ni3Al superalloys with 20-25 at.% Al consist of dendritic gamma + gamma ' dual phase and interdendritic gamma ' single phase. The proportion of gamma + gamma ' dual phase gradually increases with decreasing Al contents, whereas the tensile strength and elongation gradually increase. The Ni3Al superalloys (20 at.% Al) with the most gamma + gamma ' dual phase exhibit the highest tensile strength and elongation (939 MPa and 25.7%, respectively). Fracture analysis shows that the dislocation decomposition and stacking fault shearing mechanisms allow dislocations to continuously cut through gamma ' precipitations to maintain deformation, which is responsible for high tensile strength and ductility.