Densification, microstructure evolution and mechanical properties of ultrafine SiC particle-dispersed ZrB2 matrix composites

The densification behavior along with the microstructure evolution and some mechanical properties of four ultrafine SiC particle-dispersed ZrB2 matrix composites were studied. The SiC-ZrB2 composites, with a SiC content of 5, 10, 15 and 20 vol%, were densified to near full density by vacuum hot pressing at 1,900°C under a maximum uniaxial pressure of 45 MPa. The presence of SiC greatly improved the sinterability of ZrB2. Grain growth of the diboride matrix was increasingly inhibited for larger amounts of SiC added. Elastic modulus, Poisson ratio, microhardness, flexural strength and fracture toughness were measured at room temperature. Unexpectedly, no obvious effect of the increasing amount of SiC on flexural strength and fracture toughness was found. The former property ranged from 650 to 715 MPa but was actually affected by the exaggerated size of several tenths of micrometers of sintered SiC clusters which acted as dominant critical defects. Also fracture toughness did not receive a marked contribution from the increase of the SiC content. As for the matrix, the prevailing fracture mode of the composites was intragranular, regardless of the SiC content.