Two-scale spatial reorganisation of plastic deformation accompanies temperature-dependent mechanical softening in a nanopolycrystalline BCC Al₀.₈NbTiVNi₀.₂ high-entropy alloy

Understanding how localised atomic rearrangements collectively develop into macroscopic plastic deformation remains a central challenge in nanopolycrystalline high-entropy alloys (HEAs), particularly at elevated temperatures. Large-scale molecular dynamics simulations were performed to investigate the tensile deformation of nanopolycrystalline body-centred cubic (BCC) Al₀.₈NbTiVNi₀.₂ at 300, 600, 900 and 1200 K under a constant strain rate of 1 × 10⁹ s−¹. Mechanical behaviour was interpreted using complementary structural, kinematic, energetic and connectivity analyses. Increasing temperature progressively reduced elastic modulus and strength. At the local scale, the most intense non-affine atomic rearrangements became less concentrated within a single dominant connected region and were redistributed among smaller, spatially separated clusters, whereas at the microstructural scale the already connected non-BCC framework progressively expanded and consolidated. These complementary trends demonstrate that temperature-dependent mechanical softening is accompanied by a progressive two-scale spatial reorganisation of plastic deformation within the investigated nanopolycrystalline regime. The present results establish a direct atomistic-to-macroscopic correlation and provide a coherent framework for interpreting temperature-dependent plastic deformation in nanopolycrystalline BCC high-entropy alloys.