TEM characterization of hot-pressed ZrB2-SiC-AlN composites

The impact of the AlN additive on the microstructural features and consolidation behavior of the ZrB2-SiC system was studied. For this objective, different weight percentages of AlN were added to the ZrB2-30 vol% SiC ceramics, in which 4 wt% phenolic resin was used as a binder. All specimens were hot-pressed at sintering circumstances of 1900 °C under 10 MPa for a dwelling time of 120 min. The addition of AlN had a remarkable effect on the sintering behavior of ZrB2-SiC, attaining fully dense composite samples. Although the thermodynamic study suggested the formation and consumption of several compounds over the hot-pressing, only the peaks related to carbon was detected in the XRD patterns. The thermodynamic assessment also implied the generation of a liquid phase over the sintering as the main factor in boosting the sinterability of specimens. The microstructure of as-produced ceramics was also inspected using FESEM and HRTEM images. Such micrographs endorsed the beneficial role of liquid phase sintering mechanism in forming coherent and strong interfaces among the available phases. Fractographical evaluation manifested the transgranular type as the dominant fracture mode for all hot-pressed composites.