Enhanced He irradiation damage resistance at 850 °C of Ni-based alloy via W substitution for Mo: Experiments and DFT calculations

Abstract

The Ni-26W-6Cr alloy was subjected to He ion irradiation at 850 °C with gradient-fluence (1, 3, and 5 × 10¹⁶ ions/cm²), and the defect evolution and hardening behavior were characterized. Theoretical analyses were then conducted, including: He bubble pressure estimation via Young-Laplace and equation of state, hardness increment analysis using the dispersion barrier hardening model, and defect property calculations via first-principles DFT. Competitive defect evolution under different fluences was summarized and compared with Ni-Mo-Cr. The results show that under low-to-medium (L-M) fluences, dislocation loops grow accompanied by a decrease in number, while He bubbles preferentially occupy nucleation sites to form dense high-pressure networks, thereby restricting the growth of dislocation loops. Under medium-to-high (M-H) fluences, He bubbles increase in size and decrease in number via the migration and coalescence, forming sparse low-pressure networks that enable dislocation loops to break through restrictions and grow further. This defect evolution difference caused severe hardening in the L-M stage but a negligible hardness increase in the M-H stage. Compared with the Ni-Mo-Cr alloy, the sizes of He bubbles and dislocation loops in the Ni-W-Cr alloy are reduced by 3.24 nm and 9.01 nm, respectively, and the hardness increment decreased by 0.40 GPa, which confirms the inhibitory effect of W substitution for Mo on irradiation damage at 850 °C. Density functional theory (DFT) reveals the advantages of W substitution at the atomic scale. DFT results indicate that the excellent properties of the Ni-26W-6Cr alloy originate from the easy formation of W vacancies capable of dissolving He, as well as the reduced damage to lattice stability caused by He substitution defects.