Effect of Solid Solution Temperature on Material Properties and Microstructure of Inconel 718/TiC Composites by Selective Laser Melting

Abstract

Selective laser melting (SLM) is an important additive manufacturing process. It applies focused laser energy to quickly melt and solidify material powders, and a controlled layered operation can result in a free form build that is often out of reach for machining processes. As such, it has attracted much attention in recent years. However, metal components produced by this process often have inferior mechanical properties, as compared with the counterparts by the traditional manufacturing processes. To strengthen the metal components by SLM, adding reinforcement particles and applying post treatment are regarded as the two effective ways. Although adding reinforcement particles to create metal matrix composites has been studied by researchers in literature, much fewer has been done to use post treatment processes to further improve the properties and performance of the metal matrix composites from SLM. In this study, a nano-TiC reinforced Inconel 718 composite is prepared using SLM technique. The material has 0.5 wt.% nano-TiC addition. Solid solution treatments at three levels of temperature (940, 980, 1020 °C) are carried out to evaluate the effect of the heat treatment methods on the microstructure and resulted mechanical properties of the composite material. The results of samples with and without heat treatment are also compared. SEM observations are carried out to analyze the microstructure of the composite and understand the reinforcing mechanism. Tensile tests are conducted to evaluate the mechanical properties of the formed composites. It is discovered that compared with the pure Inconel 718 by SLM, the Inconel 718-TiC composite exhibits improved ultimate tensile strength. Microscopy observation of as-built samples indicates that the dendritic structures of Inconel 718 is remarkably refined by the TiC particles. Suspected laves phase particles are observed in as-built Inconel-TiC composite, and they partially transform to large amount of needle-like δ phase during the solid solution treatment.