Activation parameters for deformation of ultrafine-grained aluminium as determined by indentation strain rate jumps at elevated temperature

The hardness and strain rate sensitivity of ultrafine-grained (UFG) aluminium was examined as a function of temperature using in situ strain rate jump indentation in a SEM at temperatures up to 250 °C. Measured strain rate sensitivities were in good agreement with earlier bulk compression measurements. Activation energies and volumes for deformation were extracted and discussed. Transitions in the deformation mechanism are observed at lower temperatures for smaller grain sizes.