Pathway engineering in polymer-derived ceramics: Transforming pyrolytic defects into structural assets via reaction-healing-reinforcement synergy

Uncontrolled phase transitions during the pyrolysis of polymer pyrolysis, characterized by severe volume shrinkage and defect proliferation, fundamentally compromise the structural integrity of polymer-derived ceramics (PDCs). This study established a pathway engineering framework by introducing ternary synergistic fillers (Ti, Si, ZrB₂/B₄C) into polycarbosilane precursor, thereby converting pyrolytic damage into a driving force for in situ densification. This controllable pathway elevated ceramic yield from 59.83% to 92.91%, enabling carbon/carbon composite joints to achieve a shear strength of 11.84 MPa at 1200 °C. This study provides a developmental strategy for regulating the phase transition of pre-ceramic polymers in extreme environmental applications.