Mechanical and Tribological Behavior of Polymer‐Derived Ceramics Constituted from SiC_xO_yN_z

Abstract

Polymer-derived ceramics (PDCs) are a new class of ceramics that are obtained from direct pyrolysis of densely crosslinked polymers. In this article, we report the mechanical and tribological properties of silicon-based PDCs. The density, the elastic modulus, the hardness, and the fracture toughness of silicon oxycarbonitride ceramics are related to their tribological (friction and wear) behavior. The mechanical properties show a strong relationship with the oxygen/nitrogen ratio in the ceramic, which was varied by annealing the specimens in nitrogen at high temperatures and pressure. The properties are enhanced by a higher nitrogen-to-oxygen ratio. In dry environments, the tribological behavior is divided into two regimes: a low-friction regime with a coefficient of friction, l, of about 0.2, and a highfriction regime with lB0.7. The transition occurs at a critical value of contact stress. This transition stress appears to be related to the onset of fracture of the ceramic, and moves to a higher value with higher modulus and hardness of the ceramic. The transition stress is successfully analyzed in terms of the influence of the elastic modulus on the fracture stress. The analysis leads to the suggestion of a residual tensile stress in the surface of the specimens of approximately 1 GPa equivalent of the contact stress. In a humid environment, the transition stress apparently moves beyond the experimentally accessible regime. In this environment, the coefficient of friction remains unchanged at lB0.2. Two hypotheses, one related to the effect of humidity on the work of fracture, and the other to the formation of a hydrated film on the surface of silicon nitride, the counterface in the tribological experiments, are proposed for this behavior.

Tribology–Structure Relationships in Silicon Oxycarbide Thin Films

“…Very little running‐in phase was observed for these samples, and friction coefficients were observed to increase with oxygen content over a range from 0.3 to 0.8. The tests were remarkably reproducible for the various radii that were used for each specimen, and the values observed were similar to those found in the literature for a nominal silicon oxycarbide material derived from silazane 29 …”

Development of Dense Filler‐Free Polymer‐Derived SiOC Ceramics by Field‐Assisted Sintering

“…The hardness values are comparable to the literature data available for SiOC specimens, 5,8,11 although the high amount of free carbon in the present samples can be detrimental for hardness. Measured hardness values are lower than those reported for SiCN or SiOCN ceramics 6,7 . This can be due to the missing rigid Si–N bonds in SiOC.…”

Additive Manufacturing of Ceramics Enabled by Flash Pyrolysis of Polymer Precursors with Nanoscale Layers

“…The coatings were characterized by Raman spectroscopy to ascertain that the polymer precursor had fully pyrolyzed. The ceramic phase contains graphene networks which yield the characteristic G and D peaks that serve as the signature of the PDC phase …”