Evaluation of Subsurface Defects Using Pulsed Thermography and Laser Shearography of Additively Manufactured AlSi10Mg Alloy Made by Laser Powder Bed Fusion Process

Abstract

Modern techniques such as laser-based additive manufacturing (LBAM) technologies are being used nowadays in many industries for the fabrication of components of complicated geometries in smaller lead times. To compete with the conventional fabrication route, additive manufacturing (AM) technology must progress with appropriate NDE methods to ensure defect-free components. The common defects noticed in the AM components are gas porosities, clusters of porosities, micro-cracks, balling, lack of fusion and layer delamination among others. This paper aims to inspect subsurface defects in AM products which are one of the more challenging issues in AM. The surface finish of the AM components in as-printed condition is not amenable for the detection of subsurface defects for NDE using contact methods, e.g. ultrasonic techniques. Laser shearography and pulsed thermography by thermal excitation are extensively used as noncontact NDT techniques for the detection of subsurface defects in composite materials. Noncontacting NDT techniques may play a significant role in the in-process inspection of  AM components, especially subsurface defects. This paper presents the capability, advantages and limitations of pulsed thermography and laser shearography techniques for the assessment of engineered defects in aluminum alloy coupon made through the laser powder bed fusion (LPBF) AM process.