Investigation of the rheological behavior of 316L stainless steel micro-nano powder feedstock for micro powder injection molding

Abstract

The rheological behavior of 316L stainless steel micro-nano powder feedstock was investigated by torque rheometer test which measured variations of mixing torque as a function of powder loading rate of the feedstock. The feedstock was prepared by mixing a bimodal powder mixture of 75vol.% micro powder (D50=4.1μm) and 25vol.% nano powder (D50=100nm) with wax-based binder. Through the torque rheometer experiment the rheological properties were evaluated by measuring viscosity in dependence with shear rate, temperature and powder loading rate. As a result, the rheological parameters as flow behavior index (n), flow activation energy (E) and the moldability (αstv) were obtained. It was found that the mixing torque was increased with increasing powder loading in three different rates. It was confirmed from the dependence of viscosity on shear rate that the micro-nano powder feedstock followed pseudo-plastic flow behavior. It was notable that the rheological parameters underwent a sudden change in the powder volume loading range of 66% to 68%. This powder loading range was consistent with the optimal powder volume loading of 66% in our previous work for powder injection molding.