Analysis on Defects in 3D Additively Manufactured Inconel 738LC by Synchrotron Radiation X-ray CT and Optimization of Process Parameters in Additively Manufacturing

Synchrotron X-ray computed tomography (CT) in SPring-8 was utilized to analyze the size and shape distribution of internal defects in Laser Powder Bed Fusion (L-PBF) manufactured Inconel 738LC. This technique enabled the detection of defects smaller than 10 μm, which are considered difficult to detect with laboratory high tube voltage X-ray CT. This was achieved due to the high signal-to-noise ratio of synchrotron X-ray CT. Based on CT image, the defects were classified according to Feret diameter and sphericity. Defects consisted only of lack of fusion (LOF) when the laser energy density was less than 40 J/mm3. These LOF defects were characterized by a Feret diameter between 3 mm and 0.2 mm, and a low sphericity less than 0.3. LOF disappeared and defects consisted of cracks and gas pores when the energy density is higher than 50 J/mm3. Cracks were characterized by a Feret diameter between 0.3 mm and 10 μm, and a sphericity of 0.3-0.7. Gas pores were characterized by a Feret diameter between 30 μm and 5 μm and a higher sphericity of 0.6-0.8. Appropriate laser energy density was 56 J/mm3 to obtain an additively manufactured body with the highest relative density (99.6%) without LOF.