Mapping the fracture regimes of nanocrystalline 3C-SiC: a multi- parameter molecular dynamics study on grain size, crack, and thermo- mechanical loading

QY Li and CK Song and K Guan and ZY Lu and XH Yang and LT Bai and QF Zeng and JT Liu, JOURNAL OF MATERIALS SCIENCE, 60, 22757-22775 (2025).

DOI: 10.1007/s10853-025-11757-x

Silicon carbide (SiC) ceramics are renowned for their exceptional mechanical properties under extreme conditions. However, the complex fracture mechanisms within coupled temperature-strain rate fields- particularly the link between microstructure and macroscopic response- remain inadequately understood. This raises a fundamental question: Is there a universal, competitive, and synergistic mechanism at the atomic scale-interacting among crystal structure, pre-existing defects, temperature, and strain rate-that governs the fracture mode transition in 3C-SiC? To explore this, we develop a comprehensive computational framework using molecular dynamics simulations, which encompass pristine single crystals and polycrystalline structures containing central cracks. Our simulations reveal a critical grain size of approximately 8 nm in polycrystalline systems, where optimal mechanical performance (ultimate stress of 48.92 GPa) is achieved. This marks the transition between the Hall-Petch and inverse Hall-Petch effects, with results aligning well with theoretical predictions (d_critical approximate to 7.9 nm). Additionally, we observe a significant 246.7% increase in the strain rate sensitivity coefficient as temperature rises from 300 to 1500 K (from 0.045 to 0.156), indicating a fundamental shift from brittle fracture to quasi-plastic deformation. Stress contour analysis further identifies three distinct fracture modes governed by the temperature-strain rate coupling: brittle cleavage (low temperature/high strain rate), microvoid coalescence (medium temperature/medium strain rate), and quasi-plastic network fracture (high temperature/high strain rate). These findings provide essential insights into the micro-damage mechanisms of SiC under extreme conditions and establish a microstructural foundation for optimizing ceramic material performance in next-generation aerospace and energy systems.

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