X-ray tomography, AFM and nanoindentation measurements for recyclability analysis of 316L powders in 3D printing process

Recyclability of the leftover metallic powder within the Additive manufacturing (3D printing) process has been less systematically investigated by the research groups although it is a usual practice in most academic and industrial laboratories to reuse the leftover powders for subsequent printing cycles. A better understanding of these mechanisms will assist in optimizing the number of times the recycled powder can be reused in the process to reduce the powder waste. We have recently focused on characterization of recycled powders left in the powder bed after the powder bed fusion process and evaluated the extent of porosity in the powder particles. X-ray computing tomography technique (XCT) has been used to analyze the concentration of porosity, inclusions and dendrites induced inside the recycled powder particles and compared that to the fresh counterparts. The XCT resolution of 2 μm was set to separately scan the powder badges for 3 hours. A roughly 10% more porosity has been calculated in reused powder particles (in at least 10 times reused power). Atomic Force Microscopy (AFM) was used to measure the roughness of the surface of powder particles which shows average roughness of 4.29 nm and 5.49 nm for the virgin and recycled powders, respectively. Nanoindentation measurement were also applied on a number of locations of the particles to compare the hardness of the virgin and recycled powders. For example, the recycled powder shows smaller a hardness of 207 GPa and an effective modulus of 9.60 GPa (average values) compared to 237 GPa and 9.87 GPa (average values) for it's virgin counterpart which can be correlated to porosities created beneath the surface. Nanoindentation was also applied on (micro and nano) polished surface of the particles under a force of 250 μN for up to 10 seconds. The stainless Steel 316L powder has been the material under study with the powder particles of average size 50 μm which were analyzed using Xradia XCT, Bruker Dimension ICON AFM and Bruker HYSITRON TI Nanoindentation systems. Further investigation is ongoing to correlate the mechanical properties of the manufactured parts to the microstructure and chemical compositions of the virgin and recycled powders.