Variation in particle size fraction to optimize metal injection molding of water atomized 17–4PH stainless steel feedstocks

Abstract

This work reports on an essential effect of rather slight size differences in water atomized 17–4PH stainless steel powder on resulting microstructure and dimensional tolerances of metal injection molding (MIM) parts. The powders of round to irregular shapes prepared in three different powder volume fractions were admixed into the paraffin wax/HDPE (50/50) binder in a double sigma mixer. After determination of critical solid loading, the rheological, molding, and sintering performance of 66 vol% solid loading feedstocks was tested on a complex-shaped MIM component. The slight differences in size fractions are reflected also in the powder shape, which was quantified through sphericity factor and aspect ratio by dynamic image analysis. The results indicate an increase in viscosity, flow instability and injection pressure, lower sintered density with enhanced dimensional deformations for feedstocks having higher amount of coarser (10–20) μm fraction accompanied with higher shape irregularity determined from sphericity factor and aspect ratio. © 2020 Elsevier B.V.