Effect of high energy ball milling on spherical metallic powder particulates for additive manufacturing

Properties, such as morphology, particle size, and hardness affect the ability of a powder to flow and bond to a surface in additive manufacturing (AM) applications. The effects of high energy ball milling on spherical copper and stainless steel powders were evaluated. Morphology of both stainless steel and copper powders, quantifiable by aspect ratio, showed larger changes due to ball-to-powder ratio (BPR, 2:1-1:10) compared to the total milling time (2-60 min). Hardness of copper increased from 53 HV0.01 in the as-received condition to 96 HV0.01 after milling for 60 min with a BPR of 1:1 or 2:1. Hardness of steel increased from 336 HV0.01 in the as-received condition to 523 HV0.01 after milling for 60 min with a BPR of 2:1. Hardness of both powders was insensitive to milling times at low BPR (1:10). At high BPR (2:1), hardness of steel increases after just 2 min of milling, while Cu changed significantly only after 60 min. Hardness was influenced more by BPR than by milling time. It is shown that a broad range of milling parameters exist where metallic powders can be processed with minimal changes to their morphology, while controlling for hardness.