Investigation of rheological behaviour of 316L stainless steel–3 wt-%TiC powder injection moulding feedstock

The rheological behaviour of powder injection moulding feedstock comprising of 316L stainless steel and 3 wt-%TiC powders was studied using a capillary rheometer. The flowability and the sensitivity of viscosity to shear rate and temperature of the feedstock were investigated and compared with those of the binder system and the 316L SS PIM feedstock. The general rheological indexes were examined through relevant equations and the influence of TiC addition on the mouldability of the 316L SS feedstock was determined. It was found that all the feedstocks are basically pseudoplastic but the values of flow behaviour index n are influenced by the TiC addition, the solid volume fraction and the temperature. In this context, the results show that TiC addition plays an important role in rheological parameters, i.e. TiC particles decrease the viscosity of PIM feedstock and this effect is more pronounced in the system comprising higher solid volume fraction. Furthermore, the flow activation energy decreases with the introduction of TiC particles, in particular at high shear rates. In other words, the addition of ceramic particles would ease the feedstock flow and suppress the sensitivity of the feedstock to strain rate and temperature variations, if a proper moulding temperature is applied. From the viewpoint of mouldability, the optimum PIM condition for the SS/TiC composite powder containing a wax based binder system was found at 55% solid volume fraction and 70°C. At this condition, the viscosity of feedstock is low enough to fulfill the requirements of a medium pressure, injection moulding process.