Phase composition, densification behavior and high-temperature strength of carbon-doped ZrB2–ZrSi2 ceramics

Sintering additive of ZrSi 2 is beneficial to low-temperature densification of ZrB 2 -based ultra-high temperature ceramics (UHTCs), nevertheless, residual ZrSi 2 would severely reduce the high-temperature strength of UHTCs. In the current work, to achieve low-temperature preparation of ZrB 2 -based UHTCs with good high-temperature strength, active carbon (C) was added into ZrB 2 –ZrSi 2 ceramics to convert the sintering additive into refractory phases of SiC/ZrC. C-doped ZrB 2 –ZrSi 2 powders were hot-pressed at different temperatures to investigate the phase composition, microstructure and densification behavior. TG-DSC, XRD and SEM results indicated that ZrSi 2 was almost entirely converted into SiC and ZrC at 1600 °C for 2h, meanwhile, a fully-dense C-doped ZrB 2 –ZrSi 2 ceramic was obtained at such sintering conditions. In addition, the high-temperature (1800 °C) strength of C-doped ZrB 2 –ZrSi 2 ceramic was 390 ± 21 MPa, which was much higher than that of the C-undoped one. The excellent high-temperature mechanical properties could be attributed to the transformation of low-melting-point phases into refractory phases.