Effect of post-processes on the microstructure and mechanical properties of laser powder bed fused IN718 superalloy

The post-processing on the additively manufactured component is of huge interest as the key to tailor the microstructure to obtain certain mechanical properties. In this present study, the effects of hot isostatic pressing, as well as heat treatment on the microstructure, phase configuration and mechanical properties of laser powder bed fused (LPBF) IN718 superalloy were systematically investigated. Three different post-processes were studied such as hot isostatic pressing (HIP), heat treatment (HT), and HIP followed by HT (HIP+HT). The HIP process effectively eliminated the Laves phase remained in the as-built microstructure and brought uniformly distributed super fine γ″ precipitates in nano-meter size. In the heat-treated microstructure, larger γ″ precipitates were promoted directly from the as-built material. In comparison the HIP+HT process caused a moderate growth of γ″. In the latter two cases, the developed γ″ significantly strengthened the material. Yield strength of IN718 was increased from 738 MPa in as-built condition to 1015 MPa and 1184 MPa after HT and HIP+HT, respectively. On the contrary the ductility in the as-built IN718 condition was reduced by more than 40% after HT and HIP+HT. This can be compared to an increase in the ductility by almost 30% when subjected the as-built specimens to only HIPping. Finally, the correlation between microstructure evolution and mechanical properties is discussed in detail.Funding: RISE IVF AB; Lighter Academy [Vinnova 2017-05200]