Synergistic enhancement of high-temperature performance and oxidation resistance in carbon fiber-reinforced lithium aluminosilicate composites via ZrB₂ incorporation

Carbon fiber-reinforced lithium aluminosilicate (Cf/LAS) composites are attractive for precision optical and aerospace applications due to their low thermal expansion. However, their use above 500 °C is limited by matrix softening and oxidative degradation. Herein, incorporating 5 wt% ZrB₂ as a multifunctional phase effectively overcomes both issues. ZrB₂ particles disperse uniformly in the LAS matrix, raising its thermal expansion and reducing mismatch with carbon fibers. This mitigates residual tensile stress at the interface, promoting a shift from weak to strong interfacial bonding. Consequently, flexural strength at 600 °C reaches 727 ± 34 MPa (a 201% gain), and the softening point rises from 520 °C to above 950 °C. In addition, the oxidation of ZrB₂ forms a B₂O₃/ZrO₂ layer that seals surface defects and catalyzes the crystallization of the residual glass phase from 600 °C, ensuring oxidation resistance up to 900 °C. Thus, 5 wt% ZrB₂ optimally balances high-temperature strength, stability, and oxidation resistance.