Effect of a weak fiber interface coating in ZrB2 reinforced with long SiC fibers

Highlights: • Production of a ZrB₂ ceramic containing continuous BN-coated SiC fibers. • TEM analysis revealed features at the nanoscale level inside fiber, fiber coating and at the coating/matrix interface. • The BN-coating for Hi-Nicalon fiber effectively hindered fiber degradation during processing. • The composite resulted more damage tolerant than monolithic ZrB₂ or ZrB₂ reinforced by discontinuous elements. • The total and inelastic WOF values were notably higher than those measured for the short fiber composites. - Abstract: This study reports the microstructural analysis and mechanical properties of a ZrB₂ ceramic containing long BN-coated Hi-Nicalon SiC fibers. A composite was produced and thoroughly characterized by transmission electron microscopy to study the interfaces at the nanoscale level. Full densification was accomplished by hot pressing at 1450 °C. The fiber in the sintered material retained its pristine aspect, confirming that the coating was effective in preventing degradation due to interactions with the matrix. Pull-out was observed on fractured surfaces, but toughness values were about 4.5 MPa√m, which was comparable to those of ZrB₂ materials with SiC additions in the form of particles or short fibers. However, the composites exhibited a controlled fracture behavior, as confirmed by a notably higher work of fracture, 140 J/m², compared with 20–30 J/m² of unreinforced ZrB₂ or ZrB₂ containing chopped fibers.