## 3 Results and Discussion  
Figure 1 shows the SEM images of the CP Ti, Al, 35 Al65V, and GA Ti-6 Al-4V powders in the research. Ti, Al, and GA Ti-6 Al-4V powders are spherical while 35 Al65V powder has an irregular shape. Most fraction of the blended powder is spherical, ensuring good moldability. The smaller Al particles effectively decrease the distance of diffusion, which is beneficial to achieve a uniform structure for B samples. Table 1 summarizes the impurity content (O, C, N) and the prices of the as-received powders. A simple calculation indicates that, in the fabrication of Ti6 Al4V alloy, the cost of the raw materials can be reduced by \(\sim\)60% by replacing the prealloyed powder for the blended powder, which is a big advantage in mass production. A homogeneous filling of feedstock into the mold depends on viscous flow of mixture into the die cavity, and this requires a understanding of the rheological properties of feedstocks [24]. Figure 2 shows the relationship between shear rate and viscosity of the B and P feedstocks. The P feedstock \begin{table}
\begin{tabular}{c c c c c} \hline
**Powder** & **O (wt.\%)** & **C (wt.\%)** & **N (wt.\%)** & **Price (USD/kg)** \\ \hline GA Ti & 0.123 & 0 & 0.009 & 220 \\ Al & 0.220 & - & - & 30 \\
35 Al65V & 0.370 & 0.027 & 0.180 & 60 \\ GA Ti-6 Al-4V & 0.176 & 0.004 & 0.025 & 520 \\ \hline \end{tabular}
\end{table} 
Table 1: Impurity contents and the prices of the raw powders in the present study. Figure 1: SEM images of (**a**) Ti, (**b**) Al, (**c**) 35 Al65V, and (**d**) Ti-6 Al-4V powders. has a lower viscosity, indicating a better flowability to be injection molded than B feedstock. The discrepancy between them gradually diminishes as the shear rate increases from 50 s\({}^{-1}\) to 10,000 s\({}^{-1}\). For injection molding, the viscosity of the feedstock is suggested to be lower than 1000 Pa*s at the shear rate range between 100 s\({}^{-1}\) and 100,000 s\({}^{-1}\)[25]. Although the viscosity of B feedstock is slightly higher than 1000 Pa*s when the shear rate is lower than 250 s\({}^{-1}\), it can be injected into the mold cavity to produce samples without black lines. The fracture surfaces of the B and P green parts are shown in Figure 3. The powders are uniformly distributed in both samples and are cladded by a thin layer of binder. No pores and other heterogeneous structures are observed in the green samples. Figure 4a shows the TG curves of polyethylene (PE), paraffin wax (PW), ethylene vinyl acetate (EVA), polyformaldehydehyde (POM) and stearic acid (SA) with a heating rate of 10 \({}^{\circ}\)C/min, revealing the decomposition behavior of the binders. It is observed that SA and POM are easily decomposed when the temperature approaches 400 \({}^{\circ}\)C. The decomposition of EVA is composed of two stages ending at 400 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, respectively. When the temperature increases to 500 \({}^{\circ}\)C, PW and PE are finally decomposed. Figure 4b shows the TG and DSC curves of a B green sample heated from room temperature to 1250 \({}^{\circ}\)C at a heating rate of 10 \({}^{\circ}\)C/min. As shown in the TG curve, two stages of weight loss are observed. The first stage (\(\Delta_{1}\)) represents the decomposition of SA, POM, and part of EVA, which stops at 400 \({}^{\circ}\)C with a weight loss of 12.7%, while the second stage (\(\Delta_{2}\)) represents the decomposition of PW, PE, and the residual EVA, which finishes at around 500 \({}^{\circ}\)C with a weight loss of 1.5%. Though the sample is tested in a protective atmosphere of flowing argon, oxidation still happens at temperatures beyond 500 \({}^{\circ}\)C. As a result, a slight weight gain can be seen in the TG curve. The melting and decomposition of the binders can also be observed from the corresponding endothermic peaks in the DSC curve. When the temperature approaches the melting point (T\({}_{\rm m}\)) of Al,  
Figure 3: SEM micrographs of the fracture surfaces of as-molded compacts prepared from (**a**) blended and (**b**) prealloyed powders.