Effect of structural support on microstructure of nickel base superalloy fabricated by laser-powder bed fusion additive manufacturing

INCONEL (R) 718 cubes with and without structural support were built by laser-powder bed fusion (L-PBF) additive manufacturing. The effect of support on the as-built microstructure was studied based on the microstructural characteristics and micro-hardness variations. Specifically, the microstructure was examined by optical microscopy, and scanning and transmission electron microscopy. The precipitates were identified via selected area diffraction supplemented by high-resolution energy dispersive X-ray spectroscopy. Micro-hardness distributions on cross sections parallel and perpendicular to the build direction were mapped. In addition, analytical equations, taking into account various laser processing parameters, material properties and support geometries, were developed to calculate the heat build-up and cooling conditions during L-PBF. The results of microstructure characterization and analytical calculation showed a marginal effect of the support on the local microstructure and hardness due to the low heat input in L-PBF. Moreover, the comprehensive set of microstructure data is useful for future work of modelling processing-microstructure relation as well as optimizing post-fabrication heat treatment.