Investigation of the Post-Processing Heat Treatments on Hot Tensile Properties of Selectively Laser Melted IN939 Superalloy

Abstract

In recent years, the Selective Laser Melting (SLM) process has become the focus of research due to its wide range of benefits and easy fabrication advantageous in the mass production of nickel-based superalloys. However, the mechanical properties of additively manufactured nickel-based superalloys are insufficient for service conditions. Therefore, heat treatment studies are necessary to achieve desired microstructures for better mechanical properties. In this concept, it is aimed to replace melt pool boundaries and to obtain more equiaxed fine grain boundaries via heat treatment studies. This study deals with the effect of post-heat treatment studies on the microstructure and mechanical properties of selectively laser-melted Inconel 939 (IN939) superalloy. As-built and heat-treated (HIP&VHT) samples were characterized via optical and electron microscopy techniques. Transition temperatures and phases were analyzed using XRD, DSC, and Thermo-Calc simulation techniques. Finally, the effect of the hot tensile test on γʹ formation and morphology in the microstructure was investigated. Overall, the study tried to provide insight into whether the post-processes are necessary for modifying microstructure and achieving optimal mechanical properties. It was observed that both HIP and VHT had a beneficial impact on the elongation in comparison to the as-built conditions. However, no noticeable differences were achieved in ultimate tensile and yield stress.