The impact of scanning strategy on cell structures in PBF-LB/M/IN718: an in situ synchrotron x-ray diffraction study

In additive manufacturing, any change of the process parameters, such as scanning strategy, directly affects the cooling rates, heat accumulation, and overall thermal history of the build. Consequently, parts built with different process parameters tend to have different levels of crystallographic texture, residual stress, and dislocation density. These features can influence the properties of the material and their development during post-processing operations. In this study, IN718 prisms were built by laser powder bed fusion (PBF-LB/M) using two different scanning strategies (continuous 67° rotations around the build direction, ROT , and alternating 0°/67° scans, ALT ) to provide two different as-built conditions. In situ time-resolved synchrotron diffraction was performed during a solution heat treatment at 1027 °C for 1 hour. Ex situ scanning electron microscopy was used to support and complement the in situ observations. An approach to quantify the effect of elemental microsegregation at the cell walls is developed based on the deconvolution of asymmetric γ-nickel matrix peaks. Following this approach, the scanning strategies are shown to affect the as-built fraction of cell walls in the material, resulting in a difference of approximately 5%, in weight fraction, between ROT and ALT (19% vs. 24%, respectively). This microsegregation was observed to be rapidly homogenized during the heating ramp, and no significant changes to the peak shape in the γ peaks occurred during the isothermal part of the heat treatment, regardless of the scanning strategy. • An in situ approach is presented to quantify cell wall density in PBF-LB/M/IN718 • The scan strategies affect the density of cell walls in the as-built material • Microsegregation and Laves phase are homogenized during the heating ramp • The isothermal hold does not promote significant further changes past 10 minutes • After the heat treatment, cell wall conditions are similar for both scan strategies