Site-specific Cu clustering and precipitation in laser powder-bed fusion 17–4 PH stainless steel

Abstract

Thermal gyrations inherent to metal additive manufacturing (AM) result in complex microstructural heterogeneities that are linked to the process parameters, geometry, and alloy composition. AM 17–4 precipitation hardened (PH) stainless steel displays heterogeneities due to its multi-phase microstructure where different as-built phases have been reported. These phases include austenite, martensite, and ferrite, as well as varying degrees of AM induced Cu clustering and/or precipitation. To enable a systematic study of the evolution of these strengthening phases, we utilize a non-standard concentric scan strategy to achieve variations in thermal conditions across a build. Using atom probe microscopy and thermal modeling, we show that the response of Cu varies across the build from no clustering at the outer regions to an increased tendency for Cu precipitation towards the center. Our results will enable the tuning of processing parameters to achieve homogenous Cu precipitation, and thus improve mechanical properties of AM 17–4 PH.