An X-ray microtomography study of particle morphology and the packing behaviour of metal powders during filling, compaction and ball indentation processes

Abstract

The ball indentation method could be used to characterise powder packing and flow behaviours, particularly for the spreading stage of additive manufacturing (AM). However, there is no sufficient understanding of the powder packing state during the indentation process. In this paper, the X-ray microtomography has been used to characterise the particle morphology and visualize the packing behaviour of two grades of Ti6Al4V powders used in AM (gas atomized, GA, and hydride-dehydride, HDH), during the process of die filling (loose), consolidation (compacted) and ball indentation (indented). The packing fraction is found to slightly reduce under the indenter for GA powder (spherical shape) due to the dilation, while it does not change for HDH powder (irregular shape), suggesting it could be under a critically packed state. The packing fraction for both powders increases from central zone towards the wall due to the lower coefficient of friction for particle-wall than that of particle-particle.