An in situ double‐layer coating with tunable surface topography for enhancing thermal stability of Si–C–B–N ceramic fibers

Abstract Si–C–B–N fibers with suitable surface coating are benefit their application on reinforcing ceramic matrix composites with excellent mechanical properties. In this study, we reported an environmentally friendly and highly efficient technique to prepare in situ BN coating on Si–C–B–N fibers by annealing at above 1800°C in N 2 atmosphere. The BN coating showed a double‐layer structure: a rough layer coating with amounts of BN nanoparticles that formed via vapor–solid mechanism, and a BN(C) coating with thickness to above 380 nm that formed under the driving and chemical bonding by N 2 atmosphere. The Si–C–B–N fibers with in situ double‐layer coating could present strength retention up to 81.3% (1.60 GPa) after annealing at 1900°C in argon atmosphere, showing excellent thermal stability and significant potential for reinforcing high‐performance ceramic matrix composites.