Additive manufacturing of non-weldable CM247LC by powder bed fusion – laser beam of metals (PBF-LB/M) is challenging due to its high cracking susceptibility. The cracking mechanism can broadly be divided into hot cracking which occurs during the PBF-LB/M process and solid-state cracking which occurs during post-processing heat treatment. Hot cracking, in particular solidification cracking, occurs during the last stage of solidification within a solidifying melt pool and can also traverse across multiple melt pools along the build direction. On the other hand, solid-state cracking like strain age cracking occurs during the heat treatment. The residual stresses from the PBF-LB/M process and the γ′ formation stresses lead to strain age cracking. There are number of works on minimizing solidification cracking through alloy design and process parameter modification. However, less focus has been placed on reducing solid-state cracking (strain age cracking) by development of process parameters to minimize residual stresses.

This study explores the role of scan strategy in CM247LC alloy manufactured using a commercial PBF-LB/M machine EOS M290. Various scan rotation angles and re-melting strategies were explored. The solidification cracks formed during the PBF-LB/M were quantified through Light Optical Microscopy images. High-resolution Scanning Electron Microscopy along with Energy Dispersive X-Ray Spectroscopy were applied to characterize the cracking mechanism. Electron Backscattered Diffraction (EBSD) was used to characterize the micro-texture and grain morphology. Residual stress analysis were carried out using X-ray diffraction.

It was found that there is a significant effect of scan rotation on defect formation. This is primarily due to the difference in micro-texture and grain size caused due the scan rotation. Also, the residual stresses were found to be affected by the scan rotation.