Influence of oxidation healing for cracks on the strength of hot-pressed ZrB ₂-SiC-AlN ceramics

Precracks were made using a Vickers indenter on hot-pressed ZrB ₂-20 vol% SiC-10 vol% AlN ceramics (sample ZSA). The residual strength for the preindented samples oxidized at 1000°C for different durations of time was examined using a three-point bending test. According to the analysis of SEM and EDS on the surface and cross-section of the ZSA composite, the evolution of the oxidizing layer was obtained for the precracked samples. The influence of oxidation on the crack healing and residual strength was also investigated. The residual strength of the samples after oxidation increased with an increase of the oxidation time. The oxidation layer versus oxidation time and the crack-healing mechanism were also studied. When the oxidation time approached 60 min, the strength reached the maximum value. With the continuous increase of the oxidation time, the residual strength began to decrease.