Microstructure of nickel-based superalloy fabricated by selective laser melting in vacuum

Abstract

Ni-based superalloy samples fabricated by selective laser melting (SLM) in inert gas are known to have lower creep ductility than cast and wrought one. The cause is thought to be due to oxide contamination from the powder surface and the SLM-specific microstructure. In this study, we evaluated the structure of the alloy 718 fabricated by SLM in a vacuum atmosphere that can be expected to suppress oxygen contamination and control the crystal orientation by decreasing the cooling rate. As a result, the microstructure of the samples fabricated by SLM in vacuum exhibits a layered structure, which is composed of a dendrite layer parallel to the building direction and the boundary, and the total thickness corresponds to the stacking thickness. On the other hand, the thickness of the top layer was more than double the additive layer thickness. From these results, the layered structure was formed by a heat-affected layer immediately below the melted part and a dendrite layer formed by melting.