Controlling η phase distribution and its effects on carburized graded cemented carbides via extrusion additive manufacturing

Abstract

Functionally Gradient cemented carbides (FGCCs) are promising substrates for polycrystalline diamond composite (PDC). Carburization is the mainstream method for preparing FGCCs, but limited carburizing depth often leads to excessive retention of brittle low-carbon phase (η phase) in the core. This study used Powder Extrusion 3D Printing (PEP) to create dual-layered cemented carbide parts with varying thicknesses of low-carbon outer layers. After pre-sintering and carburization, three new FGCCs were produced. Results showed the η phase was confined to the interface region before carburization. With 3.84 mm carbon-depleted layer, the maximum η phase thickness was 1/10 compared to homogeneous FGCCs, with Co gradient of about 4.5 wt%. The two FGCCs with thinner low-carbon layers had smaller Co gradient with no detected η phase. Additionally, the novel FGCCs displayed enhanced fracture toughness in the core. This study achieved controlled η phase distribution, offering new insights for fabricating high-toughness carburized FGCCs without the η phase.