Annealing-induced microstructure and mechanical property evolution of helium-irradiated Cr coatings

Post-irradiation annealing (PIA) is a highly effective approach for investigating the impacts of irradiation temperature. In this work, annealing at 350–800 °C was conducted on helium ion irradiated (300 keV, 6.85 × 10¹⁵ ions/cm²) chromium coatings, and the impact of annealing temperature on irradiation defects and mechanical properties of chromium was investigated. A critical temperature threshold of 700 °C (0.45 T_m) was identified, beyond which helium bubbles exhibited a pronounced transition in coarsening behavior: gradual growth below 700 °C transitioned to rapid coarsening dominated by migration-coalescence mechanisms at higher temperatures. Concurrently, grain boundaries emerged as preferential defect sinks, facilitating bubble nucleation and growth. The swelling rate of the coating is primarily governed by bubble size and increases with temperature. Dislocation loops displayed coevolution with helium bubbles, mirroring temperature-dependent growth trends. Irradiation hardening primarily originated from dislocation pinning by both loops and bubbles. Depth-resolved nanoindentation analysis via the Nix-Gao model quantified intrinsic hardness gradients, revealing deviations from theoretical predictions attributed to unaccounted defects below 2 nm and grain-coarsening effects.