Effect of different sintering aids on thermo–mechanical properties and oxidation of SiC fibers – Reinforced ZrB2 composites

Reinforced zirconium diboride composites containing 15 vol% of Hi Nicalon SiC chopped fibers were hot pressed with addition of various sintering additives, Si3N4, ZrSi2 or MoSi2. Depending on the sintering aid, different densification temperatures were set in the range 1650–1750 °C. Temperature and additive strongly influenced the matrix/fiber interface, which in turn had a strong impact on the mechanical properties and the oxidation behavior at 1650 °C. Even the workability, performed either by conventional machining or electro discharge machining, varied depending on the sintering additive and the secondary phases formed in the system. The system containing Si3N4 turned out to have the highest mechanical properties, but intermediate oxidation resistance; the composite containing ZrSi2 had the lowest sintering temperature, but displayed the worst oxidation resistance, and finally the composite containing MoSi2 showed intermediate mechanical properties, but the highest oxidation resistance and lowest degree of damage upon machining. Preliminary measurements of thermal shock resistance by the water quenching method were also carried out.