## 2 Materials and Methods  
This study used Inconel 718 metallic powder which is a nickel-based super-alloy was provided by Sandvik Osprey Powders (Neath, UK). The Inconel powder's volume loading is equal to 60% (92 wt %). Its chemical composition is presented in Table 1. The metal-powder particles obtained by atomization with water have a spherical shape and a diameter \(d_{90}\) of less than or equal to 32 \(\upmu\)m. Inconel is being investigated more and more as a structural alloy for producing aeronautic components by metal-injection molding because of its higher resistance to oxidation, excellent performance at high temperatures (high strength up to 1400 \({}^{\circ}\)C), and its impact strength [30; 31]. The components' multi-component binder is usually composed of three different ingredients (surfactant, rheofluidifiant, the rigidifying, etc.) [6]. This study used the binder formulation previously investigated by [PERSON] et al. [6]. The multi-component binder volume is composed of 16% polypropylene (PP) provided by Sabic (Paris, France), 22% polyethylene glycol (PEG), and 2% stearic acid (SA) purchased from EMD Millipore Corporation (Billerica, MA, USA). The PP strengthens the injected components to rigidify the green-part structure and allow for manipulation after debinding. The PEG, which is a water soluble polymer, gives the binder fluidity during the injection step. The SA is a long-chain polymer that prevents the metallic powders from aggregating, to assure some homogeneity inside of the feedstock. The characteristics of the binder components and their weight fractions are given in Table 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Ni** & **Fe** & **Cr** & **Nb** & **Mo** & **Ti** & **Al** & **C** \\ \hline
52.5 & 19.0 & 19.0 & 5.3 & 3.0 & 0.9 & 0.5 & 0.0 \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical composition in mass percentage of the Inconel 718. The elaborated feedstock was assembled in a twin-screw Brabender mixer provided by Brabender GmbH & Co. KG (Duisburg, Germany) with a 50-cm\({}^{3}\) mixing chamber; it can reach a maximum temperature of 773.15 K. It consists of two screws that are especially adapted for highly loaded mixtures with metallic powders. The powder and binder were mixed for 45 min at 30 rpm and 443.15 K. After blending the feedstock, the injection-molding process was performed using an Arburg 2205 hydraulic injection-molding press provided by ARBURG GmbH & Co KG (Lossburg, Germany) equipped with a cylindrical mold cavity with an injection volume between 3 and 12 cm\({}^{3}\). The equipment dedicated to the MIM process has an anti-abrasive and bi-metallic single-screw barrel with a 15-mm diameter and a 600-mm length. The maximal injection pressure can reach 250 MPa. The maximum injection temperature was 673.15 K and the maximum injection flow was approximately 22 cm\({}^{3}\)/s. The injection pressure was 180 MPa, and the temperatures of the injected feedstocks and the die-cavity mold were 443.15 K and 318.15 K, respectively. The specimens used for the supercritical debinding were 15-mm long with a diameter of 10 mm. The weights of the injected cylindrical specimens had a mean deviation of 0.2 g; thus, showing the good homogeneity of the injected components, see Figure 1.  
During the debinding step using supercritical CO\({}_{2}\) equipment provided by SEPAREX Supercritical Fluid Technology S.A. (Champigneilles, France), the components were placed in a temperature and pressure-controlled enclosure under a CO\({}_{2}\) flow. Before starting the debinding process for each temperature condition, the components were weighed and inserted in the autoclave under environmental conditions. As shown in the Figure 2a, gaseous carbon dioxide (1) is extracted from the bottle by a valve (2) at the beginning of the process. It is then cooled to a liquid state (3) and directed towards a pump (4) that controls the pressure.