Microstructure and mechanical properties of heat-treated Inconel 625 alloy obtained by wire electron-beam additive manufacturing

The paper describes the features of structure formation of heat-resistant alloy Inconel 625 obtained by wire electron-beam additive manufacturing (WEBAM) technology and then subjected to quenching at 1200 °С and two-stage quenching at 1200 – 1000 °С. Heat treatment was carried out in a vacuum furnace, in a low vacuum environment of –1 Bar, inert gas (Ar) blowing was used for accelerated cooling. Using high-precision analytical equipment, the authors studied the microstructure, phase composition and mechanical properties of the samples in the sections along and across the deposition direction. When examining the sample in the cross-section along the deposition direction, three characteristic zones were identified: base metal zone, reheating zone, and zone of change of the crystallization front. They have different structure and, as a consequence, the difference in structure-sensitive mechanical characteristics. It was found that in the deposition process in the base layer zone, due to the material low thermal conductivity, there is an accumulation of heat, leading to the release of orthorhombic phase δ-Ni₃(Nb, Mo) in the interdendritic space. The chosen quenching temperature allowed to correct the dendritic morphology, with the formation of coarse grains of 0.3 – 0.5 mm and complete dissolution of δ-phase in γ-Ni matrix. The two-stage quenching is accompanied by isothermal release of δ-phase at grain boundaries and within grains, leading to dispersion hardening of the alloy. Uniaxial tensile tests at room temperature were carried out and numerical values of tensile strength (σ_v), yield strength (σ_t) and relative elongation (δ₅) were determined. The best combination of mechanical characteristics was obtained by two-stage quenching of the alloy.

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