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.

Automated summary

In this study, Ni3Al alloys with Al equivalents ranging from 17 to 25 at.% were successfully fabricated by adjusting the relative feeding speed. It was found that the microstructure and mechanical properties of the alloys were significantly influenced by the Al content. With increasing Al content, the alloy's microstructure changed and the tensile strength and elongation gradually increased. Fracture analysis of the final alloy materials revealed the mechanism behind the high tensile strength and ductility.