Revealing effect of interfacial bonding on fracture toughness in polycrystalline diamond with medium-entropy alloy binder

The interfacial strength has a significant impact on mechanical properties of diamond composites. In this work, polycrystalline diamonds (PCDs) with medium-entropy alloy (MEA) binders and traditional Co binder were prepared at high-pressure and high-temperature. Microstructures and interfacial strengths are carefully characterized using TEM. The results show that diamond particles are well bonded to form skeletons in all PCDs. The interfaces between MEA binders and diamond are fully coherent. Due to the effect of Cr element and Cr-carbide, the PCD with Co₅₀Ni₄₀Fe₁₀-Cr₃C₂ binder exhibits the highest interfacial bonding strength (1176.6 MPa) and highest fracture toughness (9.97 MPa m^1/2). The mechanical analyses indicate that both the interface and diamond skeleton have important effects on the fracture toughness of PCD. The interface with a higher bonding strength, a higher engineering strain and a higher elastic modulus can endure more stress, thereby improving the fracture toughness.