Analysis of Seeded Defects in Laser Additive Manufactured 300M Steel

Abstract

This research activity was initiated to better assess the capacity for traditional nondestructive testing (NDT) approaches to ascertain the defects inherent to materials fabricated through a directed energy laser additive manufacturing (LAM) process. A methodology was developed to intentionally seed defects in 300M steel specimens through intermittent modification of fabrication parameters. Several 300M steel specimens were fabricated and the concentration of defects or bulk density was characterized using optical microscopy and variations of the Archimedes’ principle. Specimens were then evaluated using NDT (radiographic testing, ultrasonic testing). Results show that by using n-hexane as the displacement liquid, the Archimedes’ principle was found to have repeatability in density values of 0.1 ± 0.1 %. The results reveal the unique defects produced through the LAM process and the limitations for conventional NDT techniques to adequately detect defects in LAM materials. Ultrasonic testing was found to be a promising tool for assessing the LAM defect distribution. Future work will focus on LAM alloys with higher densities and relate microstructure and defects to overall material performance.