Detection of Defects in Additively Manufactured Metals Using Thermal Tomography

Quality control of additively manufactured (AM) metallic structures is essential prior to deployment of these structures in a nuclear reactor. We investigate the limits of detection of sub-surface porosity defects in AM stainless steel 316L using thermal tomography nondestructive evaluation method. Thermal tomography reconstructs spatial thermal effusivity of the structure from time-dependent surface temperature measurements of flash thermography. Our studies are based on computer simulations of heat transfer through solids using COMSOL software suit. Using the model of layered media, in which defect in a solid is represented with a layer of un-sintered metallic powder with appropriate thermophysical parameters, we obtain depth profile of thermal effusivity for the structure. Computer simulations indicate that at 1 mm depth, layers of 50 mu m thickness are detectable in SS316L.