Abstract
Selective laser melting (SLM) is widely used for forming metals due to its complexity in geometrical design. Defects are unavoidably introduced in the manufacturing process, which requires post-processing. But it leads to grain growth. In this work, a series of post-heat treatments were used to study the effect of δ phase precipitation on grain growth and mechanical properties in SLM Inconel 718. Optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to study the microstructure of the specimens. The results showed that the precipitation of the δ phase increased with increasing aging time and that the growth of grains was inhibited by the δ phase. After 750 °C pre-aging for 48 h, the solution-treated specimen had the optimum strength and plasticity.

Key words
δ phase, grain growth, SLM, Inconel 718, heat treatment

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