The effect of mechanical milling for enhanced recycling Ti6Al4V powder from machining chips

This study investigates the optimization of mechanical milling parameters to enhance the recycling of Ti6Al4V machining chips, addressing a significant challenge in sustainable materials processing. The influence of ball-to-powder ratio (BPR) and ball size distribution on powder characteristics, including crystallite size, particle size, and phase composition, was systematically examined. Key findings include a 30% reduction in crystallite size, with the smallest crystallite size of 51.6 nm achieved at a BPR of 10:1, as determined by Rietveld refinement. Dynamic light scattering (DLS) measurements revealed the smallest average particle size of 220.09 nm for a 20:1 BPR with a 25:75 wt% ball size ratio. Energy-dispersive X-ray analysis (EDAX) confirmed the highest Ti content (76.62 wt%) in the 10:1 BPR sample, highlighting the correlation between milling parameters and chemical purity. Electron microscopy showed that ball size distribution significantly influenced particle morphology, with a higher fraction of smaller balls producing a more uniform particle distribution and spherical morphology. Additionally, annealing-induced phase transformations were analyzed, revealing the conversion of TiO into TiO₂ under specific conditions. This study demonstrates that optimized milling parameters can reduce crystallite size and improve particle morphology while achieving high chemical purity, laying the groundwork for practical applications in materials recycling and advanced manufacturing. The findings also show the potential for producing single-phase TiO₂ powders for use in paint and cosmetic products through tailored heat treatment processes.