Tailoring the microstructure and tensile properties of additively manufactured IN 718 alloy via adding Y2O3

Abstract

The long chain-like Laves phase is an important factor leading to fracture failure of additively manufactured IN 718 alloy. To improve the strength and ductility of IN 718 alloy fabricated by laser direct energy deposition (LDED), the influences of adding Y₂O₃ on the Laves phase morphology, twins fraction, and γ″/γ′ phases distribution both in as-deposited and heat-treated IN 718 samples were systemically investigated. First, LDED-fabricated IN 718 with 0.6–2.0 wt% Y₂O₃ additions were systematically analyzed. It was found that the chain-like Laves phases were transformed into refined granular shape after adding Y₂O₃. The Laves phases fraction of Y1.2 sample (adding 1.2 wt% Y₂O₃) reduced by about 49.5 % than IN 718 sample. Second, the as-deposited samples were subjected to heat treatment. Notably, the HT-Y1.2 sample exhibited a higher twin fraction of 51.5 % along with reduced grain sizes and dispersed γ″/γ′ phases compared with the HT-IN 718 sample. The tensile results indicated that the HT-Y1.2 sample achieved a better combination of strength and ductility (UTS = 1294.66 MPa, EL = 17.5 %) owing to the refined grains, higher proportion of twins and higher content of γ″/γ′ phases with dispersed distribution. This study provides guidance for LDED-fabricated Ni-based alloys with excellent strength and ductility.