March 10-15, 2019
A key issue that has appeared in the last twenty years is the availability of certain materials. Cobalt is considered as a critical raw material since it is massively used in batteries for electrical cars . Cobalt is also the usual binder in cemented carbides because it gives excellent hardness to toughness ratio at the tungsten carbide parts. There is a tendency to replace cobalt by other binders such nickel or iron  but cobalt remains the best one. Recycling old WC parts is a solution to limit the use of raw cobalt powder and to keep the benefits of the cobalt as metallic binder in cemented carbides.
The recycled powder has been provided by the company Höganäs S.A. Belgium. It contains 7.5 wt% cobalt with an average WC particle size about 45 µm. The as-received powder has a very low sinterability . To enhance the sintering processes, the powder has been milled with the addition of cobalt beforehand doped with 20 wt% Cr3C2 . Two powders have been prepared: WC-10(Co+Cr3C2) and WC-15(Co+Cr3C2).
The powders have been sintered with two sintering technologies: vacuum sintering (VS) and spark plasma sintering (SPS). In vacuum sintering, the samples have been heated with 4°C/min to reach 1400°C for 1h. In SPS, the samples have been heated with 150°C/min to reach 1200°C for 10 min. The pressure applied during SPS was 50 MPa.
The density of the samples was characterized before the samples were mounted into resin and polished. The microstructure before and after etching was evaluated, as well as the mechanical properties (hardness and toughness). X-rays diffraction was used to characterize the crystallites growth appearing during the sintering and the prospective change in phases.
The results show that the mechanical properties are 10% higher for SPS than for VS. It is explained by the smaller crystallite size and the higher density. No disturbing phases, such the brittle eta-phase or graphite was found in the XRD patterns.
The authors would like to thank the company Höganäs for providing the powder and the Belgian Ceramic Research Center (BCRC) for the SPS experiments.
 CDI, “Cobalt Development Institute.” [Online]. Available: https://www.cobaltinstitute.org/.
 T. W. Penrice, “Alternative binders for hard metals,” J. Mater. Shap. Technol., vol. 5, no. 1, pp. 35–39, 1987.
 A. Mégret, A. Thuault, C. Broeckmann, S. K. Sistla, V. Vitry, and F. Delaunois, “Frittage des carbures de tungstène-cobalt recylés [Sintering of recycled tungsten-cobalt carbides],” in MATERIAUX 2018, 2018.
 V. I. Stanciu, V. Vitry, and F. Delaunois, “Effect of doped binder on the microstructure of a WC-Co composite,” in Euro PM2018 Congress & Exhibition,201
Alexandre Mégret, Véronique Vitry, and Fabienne Delaunois, "Effect of the addition of doped-cobalt on the properties of recycled tungsten carbide powder sintered by SPS" in "Electric Field Enhanced Processing of Advanced Materials II: Complexities and Opportunities", Rishi Raj, University of Colorado, USA Olivier Guillon, Forschungzentrum Jülich, Germany Hidehiro Yoshida, National Institute for Materials Science, Japan Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/efe_advancedmaterials_ii/49