Pressureless sintered in situ toughened ZrB2–SiC platelets ceramics

ZrB2–SiC composite ceramics were densified by pressureless sintering with addition of Si3N4 or MoSi2 at temperatures that induced SiC anisotropic growth from particles to platelets, within a ZrB2 matrix with rounded grains. Si3N4 addition resulted in the formation of large amounts of liquid phase which enhanced mass transfer mechanisms in terms of matrix grain growth and homogeneous distribution of SiC platelets having an aspect ratio of 3. On the contrary, MoSi2 helped the densification with local formation of liquid phases leading to a finer matrix with finer SiC platelets, though more agglomerated and with a lower aspect ratio (about 2). These different microstructures had very different fracture properties values, namely a toughness of 3.8 MPa m1/2 and a strength of 300 MPa for the Si3N4-doped composite; toughness of 5 MPa m1/2 and strength of 410 MPa for the MoSi2-doped one.