Investigation of novel post-thermal treatments of alloy 718 fabricated by modulated laser powder bed fusion

The aim of this work is to determine the impact of post-thermal treatments on the mechanical properties and microstructure of alloy 718 superalloy manufactured through modulated laser powder bed fusion. Three post-thermal treatments at 980 °C and 1200 °C with and without hot isostatic pressing are utilised, followed by standard ageing procedure. The tensile mechanical properties, microstructure, crystallography, morphology, fracture impact and hardness after each heat treatment are determined. It has been found that the heat treatment procedure at 980 °C significantly affects the tensile properties while leading to no change in grain size or orientation, and formation of twined grains. A temperature of 1200 °C with and without pressure causes considerable grain growth in comparison with the as-built and 980 conditions and significant formation of twinned grains. Hot isostatic pressing was found to produce the tensile mechanical properties close to those of wrought alloy 718.