Influence of Nb on the Microstructure and Fracture Toughness of (Zr0.76Fe0.24)100−xNbx Nano-Eutectic Composites

The present study demonstrates the evolution of eutectic microstructure in arc-melted (Zr0.76Fe0.24)100-xNbx (0 ≤ x ≤ 10 atom %) composites containing α-Zr//FeZr₂ nano-lamellae phases along with pro-eutectic Zr-rich intermetallic phase. The effects of Nb addition on the microstructural evolution and mechanical properties under compression, bulk hardness, elastic modulus, and indentation fracture toughness (IFT) were investigated. The Zr-Fe-(Nb) eutectic composites (ECs) exhibited excellent fracture strength up to ~1800 MPa. Microstructural characterization revealed that the addition of Nb promotes the formation of intermetallic Zr54Fe37Nb₉. The IFT (KIC) increases from 3.0 ± 0.5 MPa√m (x = 0) to 4.7 ± 1.0 MPa√m (x = 2) at 49 N, which even further increases from 5.1 ± 0.5 MPa√m (x = 0) and up to 5.9 ± 1.0 MPa√m (x = 2) at higher loads. The results suggest that mutual interaction between nano-lamellar α-Zr//FeZr₂ phases is responsible for enhanced fracture resistance and high fracture strength.