Ductile Ni3B interphase with oxidation-induced crack healing capability for carbon fiber toughened ultra-high temperature ceramics

Ductile interphases serve as mechanical fuses to deflect matrix cracks in carbon fiber reinforced ultra-high temperature ceramic composites (C f /UHTCs). This work introduces Ni 3 B, a ductile ceramic with intrinsically low shear modulus (79 GPa) and high bulk modulus (236 GPa, G/B = 0.33), as the interphase in C f /ZrB 2 -SiC composites. A hydrothermal carbon/Ni 3 B hierarchical architecture was further engineered to resolve thermal expansion mismatch between Ni 3 B coating and carbon fibers. The optimized interface enhances fracture toughness and flexural strength by 65 % and 47 %, compared to the unmodified composites. In addition, Ni 3 B derived low-density oxides could generate volume expansion under oxidative conditions, sealing interfacial microcracks and elevating critical thermal shock temperature difference from 428 ℃ to 824 ℃. By uniquely coupling interface toughening with self-healing functionality, Ni 3 B is predicted to be a promising interphase material for future C f /UHTC composites.