Helium bubble size and density dependence of tensile mechanical properties in 3C-SiC: A molecular dynamics study

In fusion reactor environment, the accumulation of helium (He) bubbles in silicon carbide (SiC) significantly compromises its mechanical integrity. This study employs molecular dynamics (MD) simulations to investigate the influence of He bubble size and density on the uniaxial tensile deformation behavior of cubic SiC. A comprehensive range of bubble diameters (2-5 nm) and number densities (0.7-11.2 × 1023 m−3) are examined under uniaxial tension at 900 K. The introduction of He bubbles disrupts the structural integrity of SiC, resulting in a monotonous reduction in both tensile strength and Young’s modulus with increasing bubble size and density. The presence of He bubbles reduces the effective load bearing cross-section of SiC, and induces significant stress concentration around the bubble-matrix interface during tensile loading. When the He bubble volume fraction exceeds a critical threshold, these bubbles serve as preferential sites for dislocation nucleation, triggering extensive dislocation generation and propagation. This mechanism results in a premature brittle-to-ductile transition (BDT) at temperatures substantially below the intrinsic BDT threshold of pristine SiC. These findings elucidate the dual role of He bubbles in simultaneously facilitating fracture initiation while enhancing macroscopic ductility, which may have important implications for the applications of SiC-based materials in extreme nuclear environments.