Effect of processing parameters on surface roughness, porosity and cracking of as-built IN738LC parts fabricated by laser powder bed fusion

An investigation was conducted to understand how different parameters, namely laser power, scan speed and hatch spacing, influence the printing qualifies, i.e. surface roughness, porosity and crack density of the nickel-based superalloy Inconel 738LC during laser powder bed fusion. Insufficient overlap, Plateau-Rayleigh instability and Marangoni convection were identified and characterized as the factors that could deteriorate the surface quality of as-built IN738LC parts. Two leading causes of pore were determined by metallographic analysis and computed tomography as lack of fusion and keyhole, which were attributed to different energy input densities. Crack density was measured by metallographic observation. Residual stress and the time for solidification of melt were identified as the key factors that affected the crack density. Finally, the relationships between the printing qualifies and volume energy density were established by regression analysis, and the VED of similar to 48 J/mm(3) was optimal for fabricating IN738LC in the LPBF process