Microstructural evolution and mechanical properties of Inconel 718 superalloy thin wall fabricated by pulsed plasma arc additive manufacturing

Abstract

Inconel 718 thin wall has been fabricated by pulsed plasma arc additive manufacturing (PPAAM) technology, which is more convenient and cost-saving in comparison with other high energy beam additive manufacturing technologies. During PPAAM, heat input was reduced layer by layer to decrease the heat accumulation. The as-fabricated sample exhibited diverse grain morphologies at different locations. Columnar dendrites, cellular dendrites, cells and equiaxial dendrites accompanying many Laves phases, MC particles in the interdendritic regions can be observed. The largest primary dendritic arm spacing (∼41.7 μm) and Nb-rich phases area fraction (3.68%) were found in the middle region of the as-fabricated sample. After standard heat treatment, Laves phases dissolved into the matrix so that a number of γ′ and γ″ phases were formed. Besides, some rod-like δ phases could also be found near grain boundaries. The mechanisms of microstructural evolution and phases precipitation were analyzed in detail. The test values of the as-fabricated sample demonstrated a slightly higher tensile strength and dramatically outstanding ductility compared with cast Inconel 718 alloy. Applying standard heat treatment could remarkably enhance the tensile strength but decrease the ductility and make them comparable with wrought Inconel 718 alloy due to the precipitation of strengthening phases.