Adaptation of a heat-treatment condition to a precipitation-hardened nickel-based superalloy produced by laser powder bed fusion

Abstract

This study evaluated the microstructural evolution and mechanical properties of a novel printable nickel-based superalloy subjected to a solution aging treatment. The microstructures of the alloys in as-fabricated and solution-treated states were characterized using a combination of electron backscatter diffraction analysis and scanning electron microscopy. The findings indicate that the cellular crystals gradually transitioned into equiaxed grains with increasing solution temperature. The grain orientation shifts from the <001> orientation perpendicular to the building direction to a random orientation. The average grain size increased, the proportion of low-angle grain boundaries (LAGBs) decreased, and the percentage of annealing twin boundaries (TBs) increased from 0.18% in the as-fabricated state to 65.68% at 1230 °C solution treatment (ST). After lower-temperature ST, a large amount of primary γ′ and η phases precipitated in the as-fabricated alloy, with spherical and needle-like shapes, respectively. As the solution temperature increased, the quantity of the primary γ′ phase gradually decreased, and the η phase became relatively more elongated. At 1130 °C ST, both phases dissolved; following aging treatment, γ′ phase precipitated fully. High strength (1493 MPa) was achieved after direct aging treatment, attributed to the combination of cellular structures and numerous LAGBs produced during deposition with the complete precipitation of γ′ phase during aging. This study demonstrated that laser powder bed fusion alloys can achieve excellent mechanical performance through direct aging without needing ST.