An optical-based method to estimate the oxygen content in recycled metal powders for additive manufacturing

Powder recycling is key to enable sustainable and economically viable production of metal parts by fusion-based additive manufacturing (AM) processes. Determining the recyclability of a powder batch, however, requires continuous monitoring of the powder conditions during processing-notably the oxygen content-to avoid waste of resources while maintaining high build quality standards. In this work, we present a rapid and inexpensive method to acquire this information optically during the powder recoating step. Using a "powder bed scanner", we capture high-resolution optical images of different powder batches and compute their relative oxygen content by assessing the colour of individual powder particles, which is a function of the surface oxide layer thickness. We compare these measurements against those obtained using conventional techniques and confirm that our method yields higher sensitivity and more consistent results. This work pinpoints a pathway to improving the recyclability of metal powders-at least of those which are heat-tintable-through continuous monitoring of their appearance during AM processes.