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Damage behavior of He-irradiated sintered SiC at high temperatures
(Elsevier, 2025) Zhang J.; Wu Z.; Huang J.; Li J.; Wei J.; Zhang T.; Li B.; Polcar T.; Daghbouj N.
Understanding the effects of high-temperature helium (He) irradiation on the damage behavior of sintered silicon carbide (SiC) is crucial for assessing the material's stability in advanced nuclear reactors. In this study, we investigate the impact of 230 keV He ions on SiC at temperatures of 800 °C and 1000 °C, utilizing three different irradiation fluences: 2 × 1016/cm2, 4 × 1016/cm2, and 1.6 × 1017/cm2. Raman spectroscopy and transmission electron microscopy were employed to analyze various damage features, including irradiation-induced lattice strain, platelet formation, dislocation loops, and helium bubbles. Our findings indicate that over-pressurized platelets predominantly formed on the (0001) plane, with a limited number of dislocation loops detected nearby. In contrast, numerous black spot defects were observed near grain boundaries, where platelets were absent. This variation in defect distribution underscores the unique damage behavior associated with high-temperature He irradiation. The insights gained from this study are essential for understanding the structural changes and integrity of SiC materials under conditions relevant to nuclear reactor applications.
Exceptional radiation resistance of hardened amorphous SiC under high-temperature hydrogen ion implantation
(Elsevier Science, 2025) Che S.; Zhang L.; Jiang W.; Ji R.; Wang R.; Wang T.; Daghbouj N.; Polcar T.
This study provides a compelling comparison of the structural and mechanical responses of single-crystal silicon carbide (sc-SiC), nanocrystalline silicon carbide (nc-SiC), and amorphous silicon carbide (am-SiC) to hydrogen ion implantation at 650 ℃ across varying fluences. While both sc-SiC and nc-SiC exhibit blistering, microcracking, and exfoliation, am-SiC remains free of blisters, demonstrating superior resilience. Notably, nc-SiC, with its high density of stacking faults (SFs), requires a higher fluence to initiate blistering compared to sc-SiC. In sc-SiC, blistering leads to increased hardness, whereas in nc-SiC, the degradation of the SF structure results in a reduction in hardness. In contrast, am-SiC undergoes structural relaxation during irradiation, resulting in a significant increase in hardness while maintaining its structural integrity, with only the formation of nano-sized spherical bubbles observed. These findings highlight the exceptional suitability of am-SiC for nuclear applications, where resistance to radiation-induced microcracking is critical
Ab initio study of helium behavior near stacking faults in 3C-SiC
(IOP Publishing, 2024) Wang R.; Zhang L.; Jiang W.; Ejaz A.; Wang Z.; Chen L.; Wang T.; Daghbouj N.; Polcar T.
First-principles calculations are used to investigate the effects of stacking faults (SFs) on helium trapping and diffusion in cubic silicon carbon (3C-SiC). Both extrinsic and intrinsic SFs in 3C-SiC create a hexagonal stacking sequence. The hexagonal structure is found to be a strong sink of a helium interstitial. Compared to perfect 3C-SiC, the energy barriers for helium migration near the SFs increase significantly, leading to predominant helium diffusion between the SFs in two dimensions. This facilitates the migration of helium towards interface traps, as confirmed by previous experimental reports on the nanocrystalline 3C-SiC containing a high density of SFs. This study also reveals that the formation of helium interstitial clusters near the SFs is not energetically favored. The findings from this study enhance our comprehension of helium behavior in faulted 3C-SiC, offering valuable insights for the design of helium-toleran SiC materials intended for reactor applications.
Exploring radiation damage in (Hf0.2Zr0.2Ta0.2Ti0.2Nb0.2)C high-entropy carbide ceramic: Integrating experimental and atomistic investigations
(Elsevier, 2024) Zhang G.; Wang T.; Zhang J.; Zhang T.; Li J.; Zhou J.; Xu S.; Wang R.; Wu L.; Ge F.; Han W.; Li B.; Fang Z.; Polcar T.; Daghbouj N.; AlMotasem A.T.
This study investigates the intricate mechanisms that govern irradiation damage in high-entropy ceramic materials. Specifically, we synthesized (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high-entropy carbide ceramics (HECC) with a single-phase rock-salt structure using spark plasma sintering. These ceramics were then subjected to irradiation with 1.08 MeV C ions, resulting in a dose of 7.2 dpa (dpa: displacements per atom) at both room temperature (RT) and 500 ◦C. To understand the resulting damage structure, we analyzed bulk irradiated HECC samples using Grazing Incidence X-ray Diffraction (GIXRD) and Transmission Electron Microscope (TEM) at both irradiation temperatures. GIXRD analysis revealed an average tensile strain out-of-plane of 0.16% for RT irradiation and 0.14% for irradiation at 500 ◦C. In addition, TEM analysis identified a buried damaged band, approximately 970 nm thick, under both irradiation temperatures. By employing the bright field TEM imaging technique under kinematic two-beam conditions, dislocation loops of both a/3 〈111〉{111} and a/2 〈110〉{110} types within the damaged band were observed. Furthermore, our analysis indicated an increase in the average size of the total dislocation loops within the band from 1.2 nm to 1.4 nm as the density decreased. Importantly, no amorphization, precipitates, or voids were detected in the damaged band under both irradiation temperatures. Density functional theory (DFT) simulations indicated that carbon predominantly resides in 〈110〉split interstitial sites causing lattice expansion, while vacancies, particularly Nb, induced compression along the c-axis. Carbon atoms tend to bond when collectively present in the <110> split interstitial sites, contributing to the formation of interstitial loops.
AlAsqalani, Ahmed Tamer