Creation of a heterogeneous grain structure is a condition for increasing the low-temperature ductility of nanocrystalline hcp metals.

This article investigates the impact of a heterogeneous (bimodal) grain structure on the ductility of commercial purity (CP) titanium, specifically grade VT1–0, across a low-temperature range of 4.2–395 K. It demonstrates that nanocrystalline (NC) titanium with a uniform grain size below 100 nm exhibits high strength but low ductility at low temperatures due to limited intragrain dislocation activity and absence of deformation twinning. Introducing a heterogeneous grain size distribution, combining a nanocrystalline matrix with a fraction (~15%) of submicron grains, significantly enhances low-temperature ductility by enabling intragrain dislocation slip, dynamic grain growth under tensile stress, and activation of nanotwinning in larger grains. These findings suggest that tailoring grain size heterogeneity offers a strategy to optimize the strength–plasticity balance in hexagonal close-packed (hcp) metals like titanium.