Fabrication of functionally graded cemented carbide via carbon-induced shell structure binder jet 3D printing

Abstract

Listen

Translate article

Functionally graded (FG) WC-Co cemented carbide overcomes the trade-off in hardness and toughness, simultaneously achieving high hardness and high toughness. It is mainly fabricated by creating a difference in carbon content between the surface and the interior. This drives the migration of liquid-phase cobalt from the surface to the core, forming a gradient structure with a cobalt-deficient surface and cobalt-rich core. Inspired by the recent advancements in shell structure binder jetting (BJ) 3D printing, which selectively deposits binder around the model's outline to form a shell encasing the loose powder at the core, it is possible to achieve different carbon contents in the shell and core regions by adjusting the carbon content in the binder solution. In this study, a phenolic resin-based binder, yielding high carbon residue post-sintering, was prepared to investigate the impact of the carbon gradient formed by shell printing in the WC-12Co cemented carbide green part on fabricating FG WC-12Co. The effects of shell thickness and sintering temperature on the fabrication of FG WC-12Co were investigated. The results demonstrate that the binder residual carbon within the shell facilitates cobalt migration towards the core region when Co(solid)-Co(liquid)-WC three-phase coexists (1275°C-1325°C). This process results in the formation of the gradient structure with a cobalt-deficient shell and cobalt-rich core. The FG WC-12Co produced through carbon-induced shell printing yielded an increase in both surface hardness (1347.8 HV10) and transverse rupture strength (1542.91 MPa). It is feasible to fabricate FG WC-Co with adjustable Co-deficient layer thickness by controlling the shell thickness during the printing process. This study investigated the viability of fabricating FG materials through the modification of binder chemical composition in conjunction with shell structure BJ 3D printing.