## 3 Results and Discussion  
### Rheological Properties  
As discussed previously, pseudo-plastic behavior is one of the most significant traits for MIM feedstock, which means that an increase in shear rate leads to a decrease in feedstock viscosity. On the other hand, the viscosity increases with lower temperatures. Then, the required injection temperature can be decreased when pseudo-plastic behavior is present, hence minimizing defects in green components and facilitating the processing of Nd-Fe-B powder, as it is widely acknowledged that lower temperatures lessen the risk of oxidation for magnetic feedstocks. The maximum injection viscosity in the MIM process should not exceed 1000 Pa-s at the molding temperature and shear rates [44; 65]. Figure 4 illustrates representative viscosity values at two distinct shear rates for all feedstock formulations, demonstrating that viscosity decreases with increasing shear rates. As can be seen, all feedstocks have apparent viscosities lower than 1000 Pa-s at the measured shear rates, which is within the acceptable range for MIM. Feedstock A shows the highest viscosity values since it contains the highest backbone (LLDPE) content. As established by several studies on different MIM powders, the viscosity of feedstocks is often decreased by reducing the percentage of backbone in the binder system since the backbone polymer is usually a polymer with higher molecular weight and thus a higher intrinsic viscosity [66; 67]. In addition, 8.75 vol.% of SA in feedstock C reduced the viscosity to the same level as feedstock D even though feedstock C has 2.5 vol.% more LLDPE and 6.25 vol.% less PW content. Comparing feedstocks C and D at low and higher shear rates suggests that SA is more effective in reducing viscosity than PW. This is because SA has a lower molecular weight than PW and, as such, a much lower viscosity [43]. Although extremely low feedstock viscosity enables lower processing temperatures for Nd-Fe-B feedstocks, it can cause issues during compounding and injection molding, such as flash [68] and powder-binder separation [69]. The observed chamber leakage confirmed the challenges in compounding low-viscosity feedstocks during the preparation of feedstocks C and D. As can be seen by these results, having such a high amount of PW and SA simultaneously is not recommended. From the viscosity and processability standpoints, the 45-52.5 vol.% LLDPE range is acceptable in the binder formulation for the Nd-Fe-B feedstock. Feedstocks A and B have an acceptable apparent viscosity for the MIM process since they have a viscosity lower than 1000 Pa-s and shear thinning behavior. In addition, no leakage during compounding was observed. Therefore, these two feedstocks are good candidates for further optimization. Between feedstocks A and B, generally, it is preferred to use a feedstock with lower viscosity (i.e., feedstock B), which can allow the increase in powder content, resulting in enhanced mechanical and magnetic properties. The variation of pressure during capillary rheology measurements is a good indication of the viscosity stability and feedstock homogeneity [70]. Figure 5 represents the typical pressure curves during viscosity measurements of the different feedstocks at two distinct shear rates. At low shear rates (100 s\({}^{-1}\)), the material flow is stable, as shown by the constant pressure between 350 and 450 s for all feedstocks. The pressure behavior at the high shear rate (1000 s\({}^{-1}\)) for the various formulations is observed between 450 and 575 s in Figure 5. The pressure variation of the A, B, C, and D feedstocks were 0.4%, 0.4%, 0.6%, and 0.6%, respectively. As can be seen, feedstocks A and B had the lowest pressure change (i.e., 0.4%), implying a better homogeneity between the various binder components and the 55 vol.% powder loading at a temperature of 160 \({}^{\circ}\)C for Nd-Fe-B feedstock.