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

ZrB 2 -20SiC (ZS20) composite and its derivatives doped with 5 vol% Sc 2 O 3 , Y 2 O 3 , and La 2 O 3 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 La 2 O 3 (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 La 2 O 3 preferentially reacts with SiO 2 to form La 2 Si 2 O 7 , which demonstrates a more effective oxygen barrier property compared to ZrSiO 4 . Additionally, La 2 O 3 enhances the fluidity of the glass phase, effectively filling cracks, sealing pores, and blocking the penetration of oxygen.