Influence of powder size on the moldability and sintered properties of irregular iron-based feedstock used in low-pressure powder injection molding

Initially used for shaping irregular ceramic powders, manufacturing metallic parts via low-pressure powder injection molding (LPIM) from irregular powders has received very little attention. This study investigates the processability of irregular powders for fabricating high-density and low-cost metallic parts using the LPIM process. Three irregular iron-based powder lots were mixed with a low-viscosity binder, injected, debound, and sintered to evaluate their molding and sintering performances via viscosity measurements, real-scale injections, metallographic analysis, and tensile tests. The results revealed that feedstocks formulated from fine and coarse powders exhibit good moldability, predicted by their moldability indexes and validated by spiral flow distances. Furthermore, the feedstock formulated with the finer powder (i.e., 1250 mesh providing a powder particle size <10 μm) produced a homogeneous microstructure along with a low content of oxygen impurities, leading to the highest sintered relative density of ∼90%, an ultimate tensile strength of ∼225 MPa, and an elongation at break of ∼24%. These results confirm that the cost-effective irregular iron powders present a promising alternative to fabricating metallic parts via low-pressure powder injection molding compared to their relatively high-cost spherical powder counterparts (i.e., carbonyl iron powder).