Tyranno SA3 fiber–ZrB2 composites. Part II: Mechanical properties

Abstract

Part II of this article deals with the thermo-mechanical characterization of ZrB2-based composites containing 15vol% short Tyranno SA3 fiber. Fracture toughness of the composites, strength behavior at room and high temperature and local fiber properties are correlated to the microstructural features outlined in Part I. The fracture toughness increased of 20–35% as compared to the unreinforced matrix, owing to a combination of pinning, crack deflection and bridging phenomena. The room temperature mechanical strength nearly halved owing to the introduction of 100–200μm long reinforcement. However, the strength at 1200°C remained around 350–450MPa, always higher than the unreinforced material, thanks to the beneficial effect of the fiber showing an increased pullout contribute at this temperature. Flexural strength at 1500°C in air dropped to 80–280MPa, depending on the sintering additive, due to fiber oxidation. The in situ properties of the fiber and matrix were measured by nanoindentation. Comparisons with analogous composites containing short Hi-Nicalon fibers are also presented and local/bulk properties correlated to microstructural features.