Effect of building direction and heat treatment on mechanical properties of Inconel 939 prepared by additive manufacturing

Abstract

This study investigated the effect of building direction (BD) and three-step heat treatment on the microstructure and mechanical properties of a nickel-based superalloy Inconel 939 produced by additive manufacturing (AM), and it revealed the differences to the conventional cast superalloy. Tensile specimens were printed in horizontal and vertical BDs, and tensile tests were performed at room temperature, 700 °C and 800 °C. Thorough microstructural scrutiny conducted through light and electron microscopy revealed microstructural differences between AM and cast Inconel 939. The columnar grain structure with a preferential orientation of <001> was typical for AM alloy, whereas polyhedral grain without any specific orientation was typical for cast alloy. Experiments showed that the AM material had much better mechanical properties than the cast material. Heat treatment resulted in a formation of a fine dispersion of spherical γ′ nanoprecipitates, triggering a considerable increase in tensile strength and a drop in ductility.