Effect of temporary post-curing coatings on the surface roughness of binder-jet printed WC–Co parts

Traditionally, tungsten carbide–cobalt (WC–Co) parts are manufactured via powder metallurgy (PM) press-and-sintering but are restricted in terms of shape and quantity. In contrast, Binder Jetting (BJT) allows to create custom shapes and complex geometries from similar PM powder feedstocks. Even though BJT of WC–Co has been shown to be possible, the process is not yet fully optimized. The intrinsic complexity of WC–Co powder results in low green density (~ 20%) parts, due to poor powder flowability and large differences in particle-size distribution. These prints tend to crack before sintering and result in rough parts after densification. This project evaluated the use of three post-curing coatings (ExOne solvent binder, Cerita 983 runner wax, and powder injection molding paraffin wax) to protect the green part and ensure better integrity and surface quality after sintering. It was found that coatings penetrated through the interlayer defects but protected the samples’ surfaces. Average (R_a) and peak-to-valley (R_z) roughness had a significant reduction in all orientations for coated samples in comparison with uncoated samples. Binder-coated samples showed the most improved roughness (~ 50% in x- and y-directions and ~ 90% in the z-direction), while sintered density (94.5 ± 3.5%), grain size (1.45 μm), hardness (87.6 ± 0.9 HRA), and indentation fracture toughness (19.3 ± 5.3 MPa·m^0.5) remained unaffected.