Investigation on high-temperature evolution and heat resistance of nearly stoichiometric polycrystalline SiC-ZrB2 fibers

Abstract

In this study, near-stoichiometric SiC-ZrB₂ fibers (C/Si atomic ratio = 1.05, oxygen content <0.2 wt%) were derived from amorphous Si-C-O-Zr-B fibers (C/Si atomic ratio = 1.25, oxygen content = 9.3 wt%) through following high-temperature evolution: deoxidation and removal of excess carbon (1280–1400 °C), crystallization and rapid grain growth of β-SiC (1400–1750 °C), and sintering densification (1600–1850 °C). The tensile strength and elastic modulus of SiC-ZrB₂ fibers with an average diameter of 8.5 μm reached 2.1 GPa and 385 GPa, respectively. The fibers possessed a carbon-rich outer surface (∼ 110 nm), a dense surface layer (∼ 3.0 μm), and highly-crystallized microstructure with a SiC grain size of ∼ 250 nm. ZrB₂ crystals and minor free carbon were distributed along SiC grain boundaries. Compared to commercial Hi-Nicalon S, Tyranno SA, and Sylramic fibers, SiC-ZrB₂ fibers exhibited significantly enhanced creep resistance between 1200–1500 °C. Furthermore, the fibers exhibited excellent thermal stability, with tensile strength retention exceeding 95 % after exposure at 1800 °C for 3 h in argon.