Effect of binder saturation and drying time on microstructure and resulting properties of sinter-HIP binder-jet 3D-printed WC-Co composites

Abstract

Binder-jet 3D-printing, a non-beam-based additive manufacturing method, is a process of selectively joining layers of powder using a polymeric binder. In this study, the effects of print processing parameters such as binder saturation (60–250%) and drying time (30–45 s) on 3D-printed WC-Co composite powder is studied. Densification is attained by sintering under a vacuum atmosphere to reach the maximum temperature of 1435 ℃ followed by hot isostatic pressing under a pressure of 6.1 MPa. Although the green density of the 3D printed samples was ~21–23%, solid volume fraction of 97% to nearly 100% and near theoretical densities of 14.10–14.35 g/cm3 were achieved depending on the print processing parameters. Microstructural characterization of the final parts reveals potential spreading defects appearing as remnant pores formed during printing at a higher binder saturation level. Additionally, Co-rich pools also appear in the final parts. X-ray diffraction shows WC and Co as the main phases and a potential η-phase formation depending on the binder saturation level. Parts with WC grain size of 1.6 ± 0.7 µm, average Vickers hardness of 1270–1320 HV60 and fracture toughness of 17–22 MPa m1/2 are attained, similar to conventionally produced WC-Co with medium grain size. Here, binder-jet 3D-printing is used to fabricate WC-Co parts with uniform microstructure and mechanical properties.