Nanoscale strain evolution and grain boundary-mediated defect sink behavior in irradiated SiC: insights from N-PED and DFT

Abstract

Understanding irradiation-induced strain in silicon carbide (SiC) is essential for designing radiation-tolerant ceramic materials. However, conventional methods often fail to resolve nanoscale strain gradients, especially in polycrystalline forms. In this study, we employ nano-beam precession electron diffraction (N-PED) to perform high-resolution, multi-directional strain mapping in both single-crystal 4H-SiC and polycrystalline α-SiC subjected to helium and hydrogen ion irradiation. The high-resolution X-ray diffraction (HR-XRD) simulations of He + H irradiated single-crystal 4H-SiC closely match the strain profiles obtained from N-PED, demonstrating the reliability and accuracy of the N-PED method. In He-irradiated polycrystalline α-SiC at high temperatures, a bubble-depleted zone (BDZ) near the grain boundary (GB) reveals that GBs act as active sinks for irradiation-induced defects. N-PED further shows strain amplification localized at the GBs, reaching up to ∼2.5 %, along with strain relief within the BDZ. To explain this behavior, density functional theory (DFT) calculations of binding and migration energies indicate a strong tendency for Si, C, and He atoms to segregate toward the GB core. This segregation reduces the availability of vacancies to accommodate He atoms and leads to local strain relaxation near the GB. Furthermore, first-principles tensile simulations reveal that Si and C interstitials mitigate He-induced GB embrittlement. Charge density and DOS analyses link this effect to the bonding characteristics between point defects and neighboring atoms at GB. These insights underscore the importance of grain boundary engineering in enhancing radiation tolerance of SiC for nuclear and space applications.

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