LAUSR

The yield strength σ0.2 of titanium polycrystals in tension and in the temperature range of 4.2–395 K is studied as a function of grain size (d) ranging from micro- to nanometer dimensions. It was found that at temperatures below ∼180 K, the σ0.2 (d) dependences are not described by the classical Hall–Petch relation, shifting instead to higher stresses at nanometer size (d). The characteristics of grain-boundary hardening observed at low temperatures are explained using theoretical models, according to which in nanometer-size grains, the diameter of a dislocation loop originating at a grain boundary is proportional to d, with the nucleation stress being σ ∼ 1/d. The critical value dnc is estimated, below which the ratio σ0.2 ∼ 1/d holds at a fixed temperature. It is established that the dnc value decreases with an increase in the temperature of the experiment.The yield strength σ0.2 of titanium polycrystals in tension and in the temperature range of 4.2–395 K is studied as a function of grain size (d) ranging from micro- to nanometer dimensions. It was found that at temperatures below ∼180 K, the σ0.2 (d) dependences are not described by the classical Hall–Petch relation, shifting instead to higher stresses at nanometer size (d). The characteristics of grain-boundary hardening observed at low temperatures are explained using theoretical models, according to which in nanometer-size grains, the diameter of a dislocation loop originating at a grain boundary is proportional to d, with the nucleation stress being σ ∼ 1/d. The critical value dnc is estimated, below which the ratio σ0.2 ∼ 1/d holds at a fixed temperature. It is established that the dnc value decreases with an increase in the temperature of the experiment.