Plasticity of the ω-Al7Cu2Fe phase

Polycrystalline samples with the Al0.693Cu0.201Fe0.106 composition, corresponding to the tetragonal P4/mnc omega-Al7Cu2Fe crystallographic structure, were synthesised by spark plasma sintering and deformed in compression under constant strain-rate conditions, (epsilon) over dot = 2 x 10(-4) s(-1), over the temperature range 650 K-1000 K. A brittle-to-ductile transition is evidenced between 700 K and 750 K. The stress-strain curves exhibit a yield point followed by softening or steady state conditions only. The upper yield stress, sigma(UYS), shows a strong temperature dependence suggesting that the rate controlling deformation mechanisms are highly thermally activated. The strain-rate sensitivity of stress characterised either by stress exponents, n(exp), or by activation volumes, V-exp, was measured by the load relaxation technique. High n(exp) values, i.e., larger than 7, associated with low V-exp, typically smaller than 1 nm(3), are measured. The Gibbs free activation energy, Delta G, deduced by integrating V-exp with respect to stress varies from nearly 2 eV at 790 K to 4 eV at 1000 K. Because plasticity of the omega-Al7Cu2Fe phase takes place at temperatures at which diffusion processes are considered as dominant, the results are interpreted in the frame of dislocation climb models proposed to account for high temperature plasticity of crystalline phases. (C) 2016 Published by Elsevier B.V.