Effect of energy density on microstructure control in precipitation hardening steel during powder bed fusion

We demonstrate how controlling the heat affected zone during laser powder bed fusion may be used to optimise the phase composition of additively manufactured (AM) components in-situ to reduce post-processing heat treatments. We showcase this approach by promoting in-situ precipitation hardening in martensitic 17-4 PH stainless steel by varying the laser energy density. We link the melting and reheating associated with the layer-wise metal consolidation to the phase evolution and local material hardness, providing guidelines to achieve ‘print and use’ strategies for precipitation hardened alloys. These processing strategies may yield AM parts with lower cost, time, and embodied energy. We propose an intrinsic heat treatment strategy for precipitation hardened alloys manufactured by laser powder bed fusion, providing a pathway to reducing production costs and embodied energy in as-manufactured parts.