Tensile deformation of fine-grained Mg at 4K, 78K and 298K.

• The mechanical properties of Mg with grain sizes between 0.9 μ m and 9 μ m have been studied at 4K, 78K, and 298 K. • The grain boundary sliding contributes to deformation at 298K in samples with grain sizes below 3 μ m , generating an inverse Hall-Petch behaviour and enhanced ductility. • At 78K and 4K, plastic deformation of Mg proceeds by dislocation glide and twinning regardless of grain size. • The relationship between grain size and mechanical properties as a function of temperature is established. [Display omitted] The impact of grain size, ranging from 0.9 μ m to 9 μ m , on the mechanical properties of commercially pure Mg is investigated at temperatures of 4K, 78K, and 298K. The mechanisms governing plastic flow are influenced by both grain size and temperature. At 4K and 78K, dominant deformation modes in Mg involve dislocation glide and extension twinning, regardless of grain size. The interactions between basal and non-basal dislocations and dislocations with grain boundaries promote an unusually high rate of work hardening in the plastic regime, leading to premature failure. The yield stress follows the Hall-Petch relationship σ y ∼ k / d , with the slope k increasing with decreasing temperature. At 298K, in addition to dislocation glide and twinning, grain boundary sliding (GBS) becomes significant in samples with grain sizes below 3 μ m , considerably enhancing the material's deformability. GBS activation provides an additional recovery mechanism for dislocations accumulating at grain boundaries, facilitating their absorption during sliding and rotation. Analysis of σ Θ relationship suggests that the basal slip is the dominant dislocation mode in Mg at 298K. Decreasing grain size suppresses dislocation activity and twinning and increases GBS, resulting in lower Θ and σ Θ values. Suppressing conventional deformation modes coupled with enhanced GBS yields stress softening, breaking down the Hall-Petch relationship in Mg below 3 μ m grain size, leading to an inverse Hall-Petch behaviour. The work reports new data on the strength, ductility, work hardening and fracture behaviour, and their variations with Mg grain size across different temperature regimes. [ABSTRACT FROM AUTHOR]