Sintering and Properties of Homogeneous and Functionally Graded Niobium Carbide-Iron Composites

Cutting tools require materials that harmonize high hardness with fracture toughness, a challenge addressed in this study through niobium carbide (NbC)-iron (Fe) composites. Homogeneous NbC-Fe systems and a functionally graded structure were investigated to optimize mechanical performance. Homogeneous composites underwent dilatometry, x-ray diffractometry and sintering analysis to evaluate linear shrinkage, densification and density. Results revealed that varying NbC/Fe ratios influenced hardness and indentation toughness, with carbide-rich compositions favoring hardness and metallic phases enhancing ductility. The graded composite, sintered via pulsed electric current-assisted sintering (PECS), demonstrated a unique R-curve behavior: surface layers (NbC-dominant) achieved peak hardness (e.g., ~ 20 GPa), while toughness increased toward the Fe-rich core (e.g., ~ 10 MPa√m). This gradient design successfully merged ceramic-like surface durability with metal-like crack resistance, addressing the intrinsic brittleness of covalent ceramics. This work highlights the potential of functionally graded NbC-Fe cermets as next-generation cutting tools, offering a scalable solution to reconcile traditionally conflicting material properties.