Pressureless sintering of ZrB2-SiC composite laminates using boron and carbon as sintering aids

A processing method common to composite ceramics with very different ZrB 2 /SiC ratios was developed in order to exploit ZrB 2 -SiC laminates comprising alternate layers with different compositions for thermal protection systems of re-entry vehicles. Ceramic laminates were made using SiC, ZrB 2 and composites with a SiC/ZrB 2 ratio ranging from 100 vol.-%SiC to 100 vol.-%ZrB 2. The preparation was performed by tape casting of a slurry, layer stacking, debinding and pressureless sintering. Boron and carbon proved to be suitable sintering aids for SiC laminates as well as for composite laminates containing SiC. In the case of composites with a ZrB 2 matrix, the second phase of SiC acted as a sintering aid. This process obtains very similar densification for specimens with very different compositions (ranging from 100%SiC to 80ZrB 2 -20SiC). The stiffness of ZrB 2 -SiC laminates increased with the ZrB 2 content increase, while the bending strength was not affected by the ZrB 2 /SiC ratio.