Effect of Laser Power on the Microstructure and Fracture of Notched IN718 Specimens Fabricated by Laser Powder Bed Fusion

This study examines the impact of laser power on the microstructure and fracture behavior of IN718 specimens fabricated using laser powder bed fusion. Single-edge notched bend specimens were fabricated with varying laser power from 140 W to 260 W, and their fracture behavior was analyzed following the ASTM E1820-23b standard. The porosity and grain morphology remained unaffected by the presence of a notch parallel to the build direction. An elastic–plastic fracture mechanics approach was used to measure J-R curves, which quantify the energy required for crack propagation. Crack initiation and growth during quasistatic loading were monitored using image analysis. The results revealed a strong correlation between crack initiation and propagation, type of porosity, and relative density. The specimen printed with the optimal laser power of 180 W demonstrated the highest relative density and the greatest resistance to crack propagation. Large non-spherical defects formed due to lack-of-fusion at lower laser power are more detrimental to the crack propagation resistance.