In-situ neutron diffraction revealing microstructure changes during laser powder bed fusion and in-situ laser heat treatments of 316L and 316L-Al1

The versatility and flexibility in laser-based layer-wise additive manufacturing processes allow for the fabrication of metallic parts with tailorable mechanical properties. Interest in microstructure control during the process has led to varying applications of laser post-exposure strategies. In this study, in-situ laser heat treatment (LHT) through subsequent laser rescanning on specific layers was performed on 316L and Al-added 316L. In-situ neutron diffraction was carried out in between the LHT steps to qualitatively assess the dislocation density within the probed volume, revealing the influence of process-induced thermal history on the recovery and recrystallization capabilities of these materials. In-situ neutron diffraction during in-situ LHT was realized by using a custom designed laser powder bed fusion system installed on the beamline. Post-mortem measurements followed by microstructural and mechanical analyses shed light on the extensive effect of the in-situ LHT on the final microstructure, validating its ability to promote recovery and recrystallization and, thus, tune the mechanical properties. While microstructural analysis permits observations at the microscopic level, it is destructive, and its local nature may limit reliability. In-situ non-destructive bulk characterization with neutron diffraction enables following the evolutionary process on larger scales, confirming the microstructure evolution phenomena within representative materials volume with greater statistics.