Supercritical Debinding Research Articles

Influence of supercritical debinding and processing parameters on final properties of injection-moulded Inconel 718

In the metal injection-moulding process, the thermoplastic polymer binder plays an essential role as it provides fluidity to the high-loaded feedstock and strength to maintain the moulded shape. The purpose of this study is to develop an environmentally friendly feedstock loaded with a super-alloy Inconel 718 powder. Different binder formulations based on polyethylene glycol (PEG), for its water solubility, and bio-sourced polymers were investigated. Poly(lactic acid)/(polyhydroxybutyrate-valerate) was investigated as a bio-sourced polymer because its miscibility with the PEG. The results are compared to a standard formulation using polypropylene and PEG developed by our research group. A micro powder of Inconel 718 (nickel-based super-alloy) was chosen to elaborate the feedstock. The chemical and rheological behaviour of the feedstock during the mixing, injection, and debinding processes were investigated, with tight control of each process. The comparative impacts of the two different debinding processes and optimum sintering parameters were investigated: one by water and one by CO2 in supercritical state. The supercritical debinding caused no damage to the components for all types of feedstock and decreased the time to remove the PEG from 48 h to 4 h. Finally, the density, microstructure, and hardness of the different samples after final heat treatment were compared. The microstructure was clearly optimized, as the γ″ phases were promoted inside the grains. The results show that the well-adapted binder and debinding process produces an Inconel 718 component with high mechanical properties (Vickers hardness of 341 ± 19 HV). Moreover, this approach can be used with other formulations, powders, and binder systems.

Supercritical Debinding of Environmentally Friendly Inconel 718 Feedstock to Metal Injection Moulding Process

In the MIM process the debinding is a long, complicated and polluting step. The supercritical fluid debinding is a new method to reduce the time of debinding, the default of the pieces and the pollution. The goal of this study is to study the behaviour of an environmentally friendly feedstock of Inconel 718. For this, a binder formulation based on polyethylene glycol, because of is water debinding properties, and bio sourced polymer was made. Polylactic acid was investigated as bio sourced polymer. The debinding is realized with supercritical CO2 as solvent. The results were compared to the traditional debinding method using water at 60°C.

Supercritical Carbon Dioxide debinding in metal injection molding (MIM) process

The conventional debinding process in metal injection molding (MIM) is critical, environmentally unfriendly and time consuming. On the other hand, supercritical debinding is thought to be an effective method appropriate for eliminating the aforementioned inconvenience in the prior art. In this paper, supercritical debinding is compared with the conventional wicking debinding process. The binder removal rates in supercritical CO2 have been measured at 333.15 K, 348.15 K, and 358.15 K in the pressure range from 20 MPa to 28 MPa. After sintering, the surface of the silver bodies were observed by using SEM. When the supercritical CO2 debinding was carried out at 348.15 K, all the paraffin wax (71 wt% of binder mixture) was removed in 2 hours under 28 MPa and in 2.5 hours under 25 MPa. We also studied the cosolvent effects on the binder removal rate in the supercritical CO2 debinding. It was found that the addition of non-polar cosolvent (n-hexane) dramatically improves the binder removal rate (more than 2 times) for the paraffin wax-based binder system.

The use of co-solvents in supercritical debinding of ceramics

Abstract Extraction of organic binders (paraffin waxes) from injected green ceramic parts, by using supercritical fluids, has proven to be very efficient (short time of extraction, no defects in the green part). The extraction is more rapid when the binder is in the liquid state due to capillary migration but the capillary pressure could damage the ceramic green body because of development of internal stresses. In turn, extraction of the binder in solid state avoid formation of defects but the kinetics of extraction by solubilisation in supercritical carbon dioxide is reduced. An organic co-solvent can be added to supercritical CO 2 in order to increase the solid paraffin molecules solubility. Polar and non polar organic co-solvents were tested and their efficiency on the solubility of the paraffin molecules were compared. The influence of the length of the chains and of the number of side groups of co-solvent molecules were examined. The extraction was also performed by adding mixed co-solvent molecules. Mixtures of polar and non polar co-solvents were introduced in supercritical CO 2 . Improved extraction by a factor 5 was obtained with n-hexadecane molecule as co-solvent, which represents a good compromise between destruction of the paraffin binder molecular cohesion, which requires, on one hand, large molecules, and mobility, which requires, on the other hand, small molecules.

Mechanisms of Binder Removal Involved in Supercritical Debinding of Injection Moulded Ceramics

Des etudes precedentes ont montre l'interet de l'extraction, a l'aide de gaz carbonique dans l'etat supercritique, des additifs organiques de mise en forme de pieces ceramiques. Elles ont permis de developper un modele, etabli a partir des equations de diffusion, qui est en bon accord avec les resultats experimentaux. Les cinetiques experimentales d'extraction, par fluide supercritique, de paraffines a bas point de fusion utilisees comme liant pour des compositions d'injection sont maintenant etudiees. Une redistribution du liant a l'etat liquide au sein de la porosite de l'echantillon pendant le deliantage supercritique est mise en evidence. L'importance de ce mecanisme et son influence sur la validite du modele sont discutees.

Supercritical Debinding of Injection Molded Ceramics

Extraction of organic additives from extrusion‐molded cylinders of alumina by a supercritical fluid is investigated. Hildebrand parameters alone are not adequate to predict conditions for optimal polymer extraction with supercritical CO2. The results obtained with two models developed for the kinetics of binder extraction suggest that polymer extraction from green samples is controlled by diffusion without development of a reaction front. The solubility and diffusivity of polymers both affect the extraction rate, with opposite pressure and temperature dependencies.