Effect of oxidation at 1100 °C on the strength of ZrB2–SiC–graphite ceramics

One standard surface crack was introduced at the center of the tension surface of the test specimens with a Vickers indenter to investigate the effect of oxidation on the strength of ZrB2–SiC–graphite ceramic. The flexural strength of the pre-cracked specimen was 371.7 MPa, which was lower than the strength of ∼500 MPa for the original ceramic. Oxidation in dry or moist air was employed for 30, 60, or 90 min. The flexural strength of the oxidized specimens increased as the oxidation time increased up to 60 min and then the flexural strength did not further increase. The flexural strength of specimens oxidized in dry air was greater than those specimens oxidized in moist air, which revealed that the compounds of glassy structure could better heal the cracks on the surface of the specimen than the compounds of lamellar structure. The strength of the oxidized specimen was comparable to the strength of the pre-cracked specimens.

► This paper is first to report the effect of the surface oxides on the flexural strength.
► The effect of flaw-healing conditions on flexural strength was investigated in detail.
► The surface microstrtucture after oxidation at 1100 ̊C in air was also investigated.