Effects of interstitial content and grain size on the strength of titanium at low temperatures

Abstract

The effects of interstitial solute content (0.1 to 1.0 at.% O eq) and grain size (1–23 μ) on the deformation kinetics and strain hardening in titanium were investigated over the temperature range of 4.2 to 650°K and compared with previous results on single and polycrystals. The flow stress is given by τ ≈ τ ∗(T,⋗g, C i) + 0.5 μb{ρ(γ, d, C i)} 1 2 where T is the temperature, ⋗g the strain rate, C i the interstitial solute content, μ the shear modulus, b the Burgers vector, ρ the dislocation density, γ the shear strain and d the grain size. Good agreement occurred between polycrystalline results, those for prism slip in single crystals and dislocation velocity measurements when a Taylor factor of 5 was used. τ ∗ is proportional to √ C i , the proportionality constant increasing with decreasing temperature and being 0.05 μ, at 4.2°K. The deformation kinetics obey an Arrhenius-type rate equation with a Gibbs free energy of activation ΔG at τ ∗ = 0 and 0°K equal to ~1.5 eV (~0.21 μ 0 b 3). It is concluded that the rate-controlling mechanism is the thermally activated overcoming of interstitial solute atoms by dislocations moving on the first-order prism planes. The effects of grain size and interstitial content on strain hardening are principally through their influence on the dislocation density.