Role of rare earth oxide modification in strengthening ZrB₂-SiC composites against oxidation and cyclic ablation

ZrB₂-20SiC (ZS20) composite and its derivatives doped with 5 vol% Sc₂O₃, Y₂O₃, and La₂O₃ were densified using hot press sintering to investigate the influence of rare earth oxides on their high temperature oxidation and ablation behavior. Isothermal oxidation testing at 1773 K indicate that rare earth oxides modification lowers activation energy and slightly accelerates weight gain during the initial phase. As oxidation progresses, the weight gain of ZS20 increases sharply. The sample doped with La₂O₃ (ZS20L5) exhibits the lowest oxidation weight gain, with a porosity of only 1.8 % after oxidation. Cyclic ablation tests at the middle-low temperature zones indicate that ZS20L5 exhibits the lowest linear and mass ablation rates. Thermodynamic analyses demonstrate that La₂O₃ preferentially reacts with SiO₂ to form La₂Si₂O₇, which demonstrates a more effective oxygen barrier property compared to ZrSiO₄. Additionally, La₂O₃ enhances the fluidity of the glass phase, effectively filling cracks, sealing pores, and blocking the penetration of oxygen.