The effect of subsequent heat treatment on the evolution behavior of second phase particles and mechanical properties of the Inconel 718 superalloy manufactured by selective laser melting

In this work, the influence of subsequent heat treatment on the evolution behavior of Laves phase, S phase and carbides, and mechanical properties were investigated systematically for the Inconel 718 superalloy manufactured by selective laser melting (SLM). Two different subsequent heat treatment schemes were employed for SLM manufactured Inconel 718 superalloy in our work: 980 degrees C * 1 h/AC + 720 degrees C * 8 h/FC to 620 degrees C * 8 h/AC (the standard heat treatment scheme, SA980) and 1080 degrees C * 1 h/AC + 720 degrees C * 8 h/FC to 620 degrees C * 8 h/AC (the optimized heat treatment scheme, SA1080). The results show that the S phase can nucleate around the residual Laves phase, and then the composite phase particles are formed at the subgrain boundaries during SA980 heat treatment of SLM manufactured Inconel 718. Moreover, the entangled dislocations around these composite phase particles can promote the initiation of microcrack during the tensile process at elevated temperature, leading to premature failure. On the other hand, two types of carbides were found to exist in the SA1080 heat-treated samples: the nanoscale TiC particles along subgrain boundaries originally formed during the SLM process, and the large-size NbC particles along the grain boundaries formed during the solution heat treatment process. The heat treatment schemes of SA1080 can achieve excellent combination of strength and elongation at room temperature and elevated temperature, which is more suitable for the subsequent heat treatment of SLM manufactured IN718.