Oxidation and Strength Retention of Monolithic Si₃N₄ and Nanocomposite Si₃N₄‐SiC with Yb₂O₃ as a Sintering Aid

Abstract

O 3 as a sintering aid were investigated. The specimens were exposed to air at temperatures between 1200°and 1500°C for up to 200 h. Parabolic weight gains with respect to exposure time were observed for both specimens. The oxidation products formed on the surface also were similar, i.e., a mixture of crystalline Yb 2 Si 2 O 7 and SiO 2 (cristobalite). However, strength retention after oxidation was much higher for the nanocomposite Si 3 N 4 -SiC compared to the monolithic Si 3 N 4 . The SiC particles of the nanocomposite at the grain boundary were effective in suppressing the migration of Yb 3+ ions from the bulk grain-boundary region to the surface during the oxidation process. As a result, depletion of yttribium ions, which led to the formation of a damaged zone beneath the oxide layer, was prevented.

Oxidation resistance and strength retention of ZrB2–SiC ceramics

“…An increase in strength after oxidation have been previously observed from silicon based ceramics such as SiC and Si 3 N 4 . 13,14 This increase was attributed to the formation of a thin, dense oxide layer that could heal the surface flaws resulting from sample processing and machining. Surface flaw healing was effective only when the oxide layer was dense and very thin.…”

“…To better drive high-temperature engineering applications of non-oxide ceramics, an understanding of the effects of oxidation on the room-temperature flexural strength of the material is essential. Considerable studies have reported strength retention for SiC and Si 3 N 4 ceramics after oxidation, 13,14 but only limited experimental work involves strength retention of ZrB 2 -based ceramics after oxidation. 15,16 Guo et al compared the flexural strength of ZrB 2 -SiC composites with nano-sized or micro-sized SiC particles before and after oxidation in dry air at 1400 • C for 10 h. 16 After oxidation, the flexural strength increased for ZrB 2 -SiC containing nanosized SiC particles, whereas the strength of the ZrB 2 -SiC with micro-sized SiC particles decreased.…”

Silicon Nitride for High‐Temperature Applications

“…The different oxidation mechanism of the Si 3 N 4 and the Si 3 N 4 –SiC composite materials has been the subject of several recent studies 109–114 . Oxygen penetrates through the protective oxidation layer (consisting of SiO 2 and silicates from the sintering additive, e.g., Y 2 Si 2 O 7 ) during operation at elevated temperatures in air.…”

Mechanical and dielectric properties of porous Si3N4–SiC(BN) ceramic

“…The technique for fabricating nano-sized ceramic by pyrolyzing polymer precursor has attracted particular interest because it possesses many unique advantages over conventional powder-based ceramic processing, such as fabricating unconventional structures [24][25][26]. In addition, the polymer-derived SiC interface plays a key role in increasing the intensity of induced second-harmonic generation [27].…”