Effect of hot pressing time and temperature on the microstructure and mechanical properties of ZrB₂–SiC

Structure–property relations were examined for ZrB₂ containing 30 volume percent SiC particulates. Two grades of ZrB₂ with initial particle sizes of 2 and 6 μm were used. Billets of ZrB₂–SiC were produced by hot pressing at 1850, 1950 or 2050 °C for 45 min. In addition, the material prepared from ZrB₂ with an initial particle size of 2 μm was hot pressed at 2050 °C for 90 and 180 min. Microstructures and mechanical properties were characterized to determine the effects of the initial particle size, hot pressing time, and hot pressing temperature on the final grain size and morphology. The average grain size of the ZrB₂ phase ranged from 2.2 to 4.7 μm. Similarly, the average grain size of the SiC phase ranged from 1.2 to 2.7 μm. Hardness and modulus of elasticity were not affected by the processing conditions with average values of 22 and 505 GPa, respectively. However, flexural strength decreased as grain size increased from a maximum of ∼1050 MPa for the finest grain sizes to ∼700 MPa for the largest grain sizes. Analysis suggested that the strength of ZrB₂–SiC was limited by the size of the SiC inclusions in the ZrB₂ matrix.