Anisotropic tensile properties and in-situ deformation behavior of Inconel 718 alloy fabricated by laser directed energy deposition

Low-temperature and short-time solution and aging heat treatment (1050 degree celsius, 15 min/WC + 720 degree celsius, 8 h/FC to 620 degree celsius, 8 h/AC) was proposed for laser repaired Inconel 718 components in consideration of the risks on the heat deformation and properties degradation for the forging body with long-term homogenization treatment. After this heat treatment, the as-built epitaxial columnar grains will be retained and prone to induce the anisotropy of tensile properties. Herein, the bulk sample of Inconel 718 alloy via laser directed energy deposition (LDED) was fabricated followed by heat treatment and the tensile properties were studied under different loading directions (the angle between loading direction and building direction xi=0 degrees, 45 degrees, 90 degrees) in detail. The heat-treated microstructure of Inconel 718 is composed of the epitaxial columnar grains, Laves phase and gamma" phase and the tensile properties present the obvious anisotropy. When xi=0 degrees, alloy possesses the best strength (yield strength, YS: 1139.93 +/- 9.87 MPa; ultimate strength, UTS: 1259.56 +/- 15.77 MPa) and optimal elongation (26.23 +/- 0.96 %). When xi=90 degrees, the YS (1019.51 +/- 10.96 MPa), UTS (1119.54 +/- 7.17 MPa) and elongation (9.15 +/- 3.77 %) are all the worst. When xi=45 degrees, YS (1023.05 +/- 13.78 MPa) and UTS (1209.85 +/- 13.37 MPa) are in the middle level and the elongation reached 21.39 +/- 1.55 %. Based on in-situ tensile results, the strength difference of alloy under different loading directions is the result of the synergistic effect of geometrically necessary dislocations (GNDs) density and Laves phase, and the plasticity difference is primarily attributed to GNDs density.