Effect of post heat treatment on the microstructure and tensile properties of nano TiC particulate reinforced inconel 718 by selective laser melting

Abstract

To strengthen the metal components by selective laser melting (SLM), adding reinforcement particles and applying post treatments are generally regarded as the two effective means. However, how post heat treatment affects the properties of nano particulate reinforced metal composites obtained by laser additive manufacturing (AM) processes has rarely been studied. In this study, Inconel 718 matrix composite reinforced by 0.5 wt% nano TiC particles was prepared using SLM. To evaluate the effect of the heat treatment routines on the performance of the SLM-produced composite, two levels of solution temperature (980 and 1100 °C) were designed, and the solution treatment was followed by a standard two-step aging (720°C for 8 h and 620 °C for 8 h). Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) observations were performed to examine the microstructure, and transmission electron microscopy (TEM) observation was conducted to characterize the morphologies of incorporated nano particles and precipitated phases. Tensile tests were conducted to evaluate the mechanical properties of the formed composites. It was found that nano particles can effectively strengthen the metal matrix under both as-built and heat-treated conditions, and the material undergoes static recrystallization during the post heat treatment. Also, it was discovered that nano TiC particles play an important role in refining the microstructure of Inconel 718 composite below 980 °C. The maximum tensile strength of 1370 MPa was observed under 980°C+ aging condition, representing a 16% increase as compared with the unreinforced Inconel 718.