Effects of heat treatment on microstructures and tensile properties of IN718/TiC nanocomposite fabricated by selective laser melting

Selective laser melting (SLM) is a powder-bed fusion additive manufacturing process that fabricates metallic parts in a layer-by-layer manner. IN718 is a nickel-based austenitic (gamma) superalloy with broad applications in aerospace, chemical, and nuclear industries. In this study, fully-dense IN718-matrix composite reinforced by TiC nanoparticles were fabricated in-situ by SLM. As-built and heattreated IN718/TiC nanocomposite was compared against pure IN718 in terms of microstructures and tensile properties. Columnar and cellular microstructure morphologies in as-built pure IN718 and IN718/TiC nanocomposite were demolished by heat treatment. Microstructure refining and grain boundary dislocation pinning effect of TiC nanoparticles improved the tensile strength of as-built IN718/TiC nanocomposite. In both as-built IN718/TiC and pure IN718, gamma and Laves phase are the major constituents while the other precipitates were suppressed by rapid solidification in SLM. Heat treatment dissolved Laves precipitates and grew gamma'/gamma'', delta, and MC/ M23C6 carbides that strengthened both pure IN718 and IN718/TiC nanocomposite. In heat-treated IN718/TiC, the TiC nanoparticles and M23C6 carbides degenerated from TiC counteracted the deficiency of delta precipitates. Therefore, heat-treated IN718/TiC nanocomposite had similar tensile strength but lower ductility than heat-treated pure IN718.