Hierarchical layered and refined grain structure of Inconel 718 superalloy produced by rolling-assisted directed energy deposition

Abstract

Additive manufacturing (AM) of nickel superalloys typically leads to large columnar grains forming along the build direction, resulting in poor and anisotropic tensile performance. In this work, a novel AM process involving directed energy deposition (DED) combined with in-situ rolling was applied to fabricate a typical nickel superalloy – Inconel 718. The results revealed hierarchical layered refined grains formed in the microstructure, due to the unique dynamic and meta-dynamic recrystallization induced by the in-situ rolling during DED. Through this, an average grain size of ∼8 µm and much weaker texture was achieved for the in-situ rolled samples. Tensile test showed that a significant increase of over 50% in the yield strength was achieved for the in-situ rolled samples at both room temperature and 650°C, while maintaining a good uniform elongation above 10%. • A rolling-assisted DED process has been applied to fabricate Inconel 718 superalloy. • Columnar to equiaxed transition of grains is achieved. • The refined grains (∼8 µm in size) exhibited hierarchical layered distribution. • Over 50% yield strength increment is achieved at both room temperature and 650°C. .