Effect of Ultrasonic Treatment on Partitioning of Alloying Elements in Inconel 625 Alloy during Wire–Feed Electron–Beam Additive Manufacturing

Abstract This study investigates the effect of ultrasonic (US) treatment, introduced through the substrate, on the macro- and microstructure, phase composition, segregation (partitioning) of alloying elements, and mechanical properties of IN625 alloy produced by wire–feed electron beam additive manufacturing (EBAM). The prolonged lifetime of the melt pool and the resulting partitioning of alloying elements in nickel–based alloys IN625 remain a significant challenge during additive manufacturing. Structural analysis revealed that the application of US–treatment through the substrate during fabrication leads to the disruption of epitaxial growth of columnar grains at layer boundaries and the formation of a fine–grained structure, thereby suppressing the pronounced crystallographic texture. At the same time, the overall degree of partitioning of Nb (Cin / Cd ~ (2.6 ÷ 2.8) wt. %) and Mo (Cin / Cd ~ 1.3 wt. %) into the interdendritic region remains virtually unchanged. Nevertheless, US–treatment alters the kinetics of phase transformations at the final stages of solidification: instead of predominantly MC–type carbides observed in the reference sample, coherent precipitates of the strengthening γ''–phase (Ni3Nb, 15–40 nm), Laves phase, and rod–like δ–phase are formed. Uniaxial tensile testing demonstrated that US treatment increases the yield strength σ0.2 by 70–100 MPa (up to 360–380 MPa) and the ultimate tensile strength σb by 150–170 MPa (up to 770–780 MPa) while maintaining high elongation ε (up to 75%) without significant anisotropy. The improvement in mechanical properties is attributed to the synergistic effect of grain refinement (Hall–Petch mechanism) and precipitation hardening due to the nanoscale γ''–phase.