Indentation creep study on ultrafine-grained Zn processed by powder metallurgy

Ultrafine-grained Zn (UFG-Zn) with the grain size of about 200 nm was processed by Spark Plasma Sintering at 300 °C from fine Zn powder. The grain boundaries in the consolidated material were decorated by ZnO dispersoids with a mean thickness of ~20 nm. The creep behavior was studied by indentation tests in the homologous temperature range of 0.87-0.91. The activation energy of the creep for UFG-Zn was found to be much larger (211-252 kJ/mol depending on the oxide content) than the value determined previously for coarse-grained Zn (152-159 kJ/mol). The activation energy increased with increasing ZnO content in UFG-Zn. X-ray line profile analysis revealed that the population of the different dislocation slip systems changed during creep deformation, indicating a considerable dislocation activity.