Nickel powders are used in various powder metallurgy applications, including sintered metal filters, catalysts, or sintered electrodes in batteries and fuel cells. Filamentary-type nickel powders are made up of highly irregular-shaped, chain-like particles; such morphology provides an advantage in the manufacturing of highly porous metal membranes for filtration applications. However, the vastly irregular shape is not optimal for the spreading of powder in powder bed additive manufacturing (AM) technologies. For example, in Binder Jetting 3D Printing (BJP), the powder bed needs to be compacted well layer-by-layer for the binder to properly adhere between layers, ensuring a printed part without cracks and with smooth surface finishing and reasonable green-part strength. BJP allows for the fabrication of porous parts with an open-cell porous structure via pores-by-processing, thereby enabling novel designs of porous membranes to be fabricated. Therefore, there is great interest in enabling the smooth powder spreading of irregular filamentary nickel powder to facilitate BJP. Here, different methodologies to resolve this issue will be discussed, including the preparation of nickel powder feedstock incorporating binder and/or pore formers. Furthermore, the resulting morphology of the sintered parts will be analysed, to illustrate the BJP porous structures formed from irregular filamentary nickel powder feedstocks. Overall, this provides a platform for understanding the issues facing powder-bed AM technologies when highly irregular-shaped powders are involved.

In printing of 316L fine porous cup shaped metal membrane, the mixed feedstock consisting of 316L powder with particle size of D50=4µm and 12 wt% of PMMA with particle size of D50=5µm powder was used. With high aspect ratio of length vs. diameter for cup’s geometry, it is found that laying cup in horizontal direction and setting layer thickness along its circular diameter during printing will shorten the printing time, and also leads to less density variation across the printed parts. Meanwhile, tilting cup in small angle from 1 to 5 degree can avoid the formation of inner crack line during printing. In sintering of printed cups, several methods in terms of laid parts in different orientation were accessed. The results showed the upward laying method is the best to be employed as it has the less deformation and also easily be scaled up for mass production. For cups laying in vertical direction by setting its length as layer thickness during printing, their open porosity after sintering is ranged from 59% to 65%. However, the difference of porosity across the same cup in three different positions, i.e., top, middle and bottom is 3.83% with the bottom is the most dense area. For cups laying in horizontal direction by setting its circular diameter as layer thickness during printing, the open porosity after sintering is ranged from 57% to 62%. The variation of porosity is within 1% across the same cup from top area to bottom area, indicating the structure is more uniform. The microstructure reveals porous structure with uniformly distributed fine pores.