Improvement in the Mechanical Properties of Additively Manufactured Ni-Co-Based Superalloy by Tailoring Microstructures

Herein, a Ni-Co-based superalloy is manufactured using selective laser melting (SLM), and the effects of heat treatment (direct aging [DA] and solution treatment + aging [STA]) on the microstructure and mechanical properties of an SLM-built Ni-Co-based superalloy are investigated. An electron channeling contrast (ECC) image of the as-built alloy shows a substructure where nm-sized carbides are present along with a dislocation network. In the DA alloy, the basic characteristics of the substructure do not change, but the dislocation density decreases, the carbide fraction increases, and a large number of gamma ' phases are formed. On the other hand, the STA alloy has very low dislocation density and exhibits gamma ' phases with a size and fraction similar to those of the DA alloy. Room temperature compression tests are conducted, and the yield strengths of the as-built, DA and STA alloys are 480, 837.5, and 750 MPa, respectively. The main underlying mechanism of improvement in the mechanical properties after heat treatment can be explained by the change of dislocation density and the fraction of carbide and gamma ' phase. Based on the abovementioned findings, this study discusses the relationship between the microstructure and mechanical properties of the SLM-built Ni-Co-based superalloy.