The role of yttrium micro-alloying on microstructure evolution and high-temperature mechanical properties of additively manufactured Inconel 718

Abstract

The effects of yttrium (Y) addition on the microstructure and high-temperature mechanical properties of Inconel 718 have been investigated. Alloys containing a range of Y (0–0.58 wt%) were fabricated using selective laser melting, followed by solution and aging heat treatment. The mechanical properties were evaluated by high-temperature (650 °C) tensile and creep tests. The results showed that Y addition up to 0.07 wt% enhanced both tensile and creep ductility. Ductility was the highest in the 0.07 wt% Y-added specimen; further increases in Y content reduced both tensile and creep ductility. The ductility improvement by the small addition of Y was attributable to the grain boundary segregation of Y, which led to the morphological change of the δ phase precipitates and the stabilization of oxygen by forming Y2O3 at grain boundaries. However, the beneficial effect of Y on ductility was suppressed when Y content exceeded 0.07 wt%, owing to the precipitation of Y-rich Ni5Y and NbC phases at intergranular and interdendritic regions. On the other hand, the specimens with high Y contents were mechanically strengthened by the solid solution of Y and by the precipitation of Ni5Y and NbC phases.