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

Abstract

A processing method common to composite ceramics with very different ZrB₂/SiC ratios was developed in order to exploit ZrB₂–SiC laminates comprising alternate layers with different compositions for thermal protection systems of re-entry vehicles. Ceramic laminates were made using SiC, ZrB₂ and composites with a SiC/ZrB₂ 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 ZrB₂ 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 80ZrB₂–20SiC). The stiffness of ZrB₂–SiC laminates increased with the ZrB₂ content increase, while the bending strength was not affected by the ZrB₂/SiC ratio.

Keywords:

• Thermal protection system
• Pressureless sintering
• Tape casting
• Composites
• Mechanical properties
• ZrB₂
• SiC

This work has been performed within the framework of the European Project ‘SMARTEES’ (G.A. n. 262749) with the financial support by the European Community. The paper only reflects the view of the authors, and the European Community is not liable for any use of the information contained therein.