Multi-laser scan strategies for enhancing creep performance in LPBF

Abstract Laser Powder Bed Fusion (LPBF) enables complex structures to be manufactured, which is attractive to industries where augmented service performance can be achieved. However, the build time of LPBF can be slower than traditional manufacturing processes, especially for higher volumes of parts. Multi-laser machines have the potential to significantly reduce process time, but there is little understanding of how interlaced scan strategies impact upon mechanical properties. The results of this work show that multi-laser scan strategies have no adverse effects on the creep properties of LPBF alloy 718 at different build orientations, demonstrating the potential of using multi-laser strategies for faster build rates without compromising the mechanical properties. Indeed, it is shown that for samples built vertically (i.e. where the build direction is parallel to the loading direction), multi-laser samples outperformed their single-laser counterparts and had a similar creep life and secondary creep rate to wrought alloy (1% difference). The single and multi-laser samples built horizontally (i.e. with the build direction perpendicular to the loading direction) and at 45° from the loading direction performed similarly and all failed soon after the onset of tertiary creep. It was also found that the failure of components could not be attributed to the interlacing scan strategies used with multi-laser processing, but rather to the build orientation and its effect on the grain orientation with respect to the loading direction and the stress state of the sample. However, the scan strategy, number of lasers, fraction area of solidified layer, powder underneath the layer and the interlayer rotation meant that the layers themselves as well as the samples were heterogenous. Despite this, the creep life for any given sample was within 73 h (i.e.17%) of its repeats, giving confidence in the results. It is therefore possible, as a result of this work, to understand the effects of multi-laser scan strategies, particularly the laser-to-laser interfaces on LPBF microstructure. Multi-laser scan strategies are shown to have no detrimental effects on the creep performance, while cutting the build time by more than half.