Quality assessment of SUS316L fabricated by metal additive manufacturing with eddy current inspection

Abstract

Guaranteeing the quality of additive manufacturing (AM) components after fabrication is very important. In this study, a discrete non-destructive evaluation (NDE) system that includes an eddy current testing (ECT) probe and a fluxgate sensor was developed. In conventional ECT, the defect detection depth is limited by the skin depth of the material under investigation and requires a high frequency of the order of MHz. However, in the NDE system, the high sensitivity of the fluxgate sensor and the use of an ECT coil make it possible to detect subsurface defects at a relatively low frequency. A double-excitation coil was used to excite eddy currents in the specimen at relatively low frequencies, whereas a planar differential coil was used as a pick-up loop connected to an input coil that was inductively coupled to the fluxgate sensor. Based on the developed NDE system, five stainless steel (SUS316L) specimens fabricated by powder bed fusion were inspected. A strong correlation was observed between the detected signals and internal porosity, which was confirmed using X-ray computed tomography images. Although this approach cannot detect the local existence of defects, it can be applied for quality assessment, such as density and distribution of porosity in metallic parts fabricated by AM.