Enhanced helium irradiation resistance in Cr-doped TiVTa refractory multi-principal element alloys via integrated multiscale modeling and experiment

Refractory multi-principal element alloys (RMPEAs) hold significant promise as structural materials for future fusion blanket systems, yet realizing outstanding irradiation resistance with low-activation compositions, high phase stability and excellent mechanical properties remains a considerable challenge. This work presents a systematic experimental and computational investigation of a Cr-doped TiVTa-based RMPEA (Ti₃₃V₃₃Ta_33.5Cr_0.5) with single-phase body-centered cubic structure, high phase stability, good mechanical properties, and enhanced resistance to He bubble formation, along with minimal irradiation hardening after He ion irradiation (2 MeV, 2 × 10¹⁶ ions·cm⁻² at 773 K). Ti₃₃V₃₃Ta_33.5Cr_0.5 achieves a reduction by more than 30 times in He bubble density (0.88 × 10⁻⁵ nm⁻³) relative to V-4Cr-4Ti, with comparable average bubble sizes (3.77 nm), and a considerably low irradiation hardening rate. First-principles calculations reveal that the introduction of 0.5 at% Cr increases the local lattice distortion parameter to 7.315 × 10⁻³, elevates the vacancy formation energy by 0.12 eV, and He solution energy to 2.55 eV, thereby suppressing vacancy generation and enhancing He trapping. Molecular dynamics simulations further demonstrate significantly retarded He diffusion and suppressed growth of large He clusters within Ti₃₃V₃₃Ta_33.5Cr_0.5 after irradiation. This integrated multiscale modeling and experimental results provide fundamental insights into the mechanisms underlying enhanced helium irradiation resistance and establish the potential of compositionally optimized TiVTa RMPEAs for advanced fusion structural materials.