Carbon control and densification of WC-8%Co fabricated by extrusion-based additive manufacturing under pressureless sintering

Abstract

In this study, WC-8%Co cemented carbide was fabricated using feedstock with paraffin/polymer binder via extrusion-based additive manufacturing method and post processing. After extracting paraffin by solvent immersion, the atmosphere in furnace for thermal debinding and sintering processing were adjusted to control the carbon content of the final sintered body. The results showed that thermal debinding under industrial hydrogen atmosphere results in the formation of decarbonized phase in the sintered body. Thermal debinding under vacuum and argon atmosphere leads to formation of uncombined carbon. Sintered under hydrogen and vacuum can effectively promote the further decomposition and transformation of residual carbon, while sintered under argon atmosphere leads to aggregation of uncombined carbon. Decarbonized phases have negative impact on the strength of cemented carbides, and excessive uncombined carbon is also detrimental defects that decrease in the strength and hardness of cemented carbides. The shrinking and densification of brown body can be accomplished when sintered at 1340 ℃, the pores were almost completely eliminated and size of print defect reduced. Sintered body show superior mechanical properties. An exorbitant high sintering temperature lead to the growth of WC grains, while excessive grain growth can worsen mechanical properties of the sintered body.