Analysis of the rheological behavior of Fe trimodal micro-nano powder feedstock in micro powder injection molding

The rheological behavior of Fe trimodal powder feedstock for mu-PIM was investigated using torque rheometer analysis. The feedstock was prepared by mixing Fe micropowder (-4 mu m) and nanopowder agglomerates containing discrete particles with sizes of similar to 300 nm and similar to 30 nm, with low viscosity wax-based binders. During the feedstock mixing, a significant increase in mixing torque was observed at powder content above 72 vol% in the feedstock, indicating the critical powder loading. The results obtained from the torque rheometer experiment at selected powder loadings of 66-74 vol% were used as fundamental rheological parameters including flow behavior index (n), flow activation energy (E), and general moldability index (alpha(stv)). In addition, the influence of shear rate, temperature, and powder loading on feedstock viscosity was evaluated. It was found that the feedstock with 72 vol% powder loading exhibited the best rheological behavior with the highest moldability parameter and homogeneous microstructure. Due to the lack of research on the trimodal system in the field of powder metallurgy and powder technology, this paper provides the possibility of applying the trimodal powder mixture to a near net-shape production technique such as PIM. (C) 2017 Elsevier B.V. All rights reserved.