Microstructure and micromechanism of fracture of Ni-Al-Cr alloy produced by dual-wire electron-beam additive manufacturing

In this paper, we provide electron microscopic and in-situ X-ray study of microstructure in an Ni-Al-Cr intermetallic alloy that has been obtained by a dual-wire electron beam additive manufacturing using commercial NiCr and Al wires. As-built material possesses a dendritic microstructure that is heterogeneous in both elemental and phase compositions. Different intermetallic phases have been identified with high accuracy using transmission electron microscopy: ordered NiAl-based aluminide with particles of disordered Ni3Al-based phase in dendritic areas, and mixture of Ni and ordered Ni3Al phase in interdendrites (all alloyed with Cr). A part of the NiAl-based phase underwent the martensitic transformation B2(NiAl)→L10 during the additive manufacturing process and post-built cooling. According to in-situ XRD analysis under heating of the alloy up to 1273 K, this transformation has a thermoelastic nature, and the L10→B2(NiAl) reverse transformation finish temperature is about 873 K. We have noticed the correlation between the phase composition and the tensile fracture micromechanism of the alloy at room temperature: brittle intermetallic B2‑NiAl, L10‑NiAl and Ni3Al-based phases are responsible for high strength but low elongation of the alloy (the tensile strength is 780 MPa and the elongation is 0.2 %). An intermetallic alloy is designed to produce intermetallic coatings or to repair bulk intermetallic details using the electron beam additive manufacturing.

1. This research was funded by the Government research assignment for ISPMS SB RAS - FWRW-2022-0005