Abstract
Strain hardening dominates the deformation process in fine-grained A1-7475 alloy in the temperature range 400 to 515 °C. It is shown that anomalously low stress exponents are obtained as a result of strain hardening in strain-rate-change tests. In order to measure stress exponents in a quasi-steady state condition, the samples must be initially deformed at a relatively high stress (≍ 10 MPa) to a relatively high strain (≍ 0.5) before initiating a strain-rate-change test. Such a procedure revealed that a stress exponent about equal to two and an activation energy (141 kJ/mole) nearly equal to the activation energy for lattice diffusion are obtained. The results are interpreted in terms of a model involving grain boundary sliding accommodated by slip following the Gifkins' “core and mantle” concept. It is proposed that strain hardening is associated with the development of a boundary-dislocation structure in the mantle region in a manner similar to the development of subgrains in the core of a grain when slip is the principal deformation mode.
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Adabbo, H.E., González-Doncel, G., Ruano, O.A. et al. Strain hardening during superplastic deformation of A1-7475 alloy. Journal of Materials Research 4, 587–594 (1989). https://doi.org/10.1557/JMR.1989.0587
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DOI: https://doi.org/10.1557/JMR.1989.0587