Elevated temperature, micro-compression transient plasticity tests on nanocrystalline Palladium-Gold: Probing activation parameters at the lower limit of crystallinity

Wehrs, Juri; Deckarm, Michael J.; Wheeler, Jeffrey M.; Maeder, Xavier; Birringer, Rainer; Mischler, Stefano; Michler, Johann

Acta Materialia 129 (2017)

In this study, we probe the activation parameters and time-dependent plastic behavior of a nanocrystalline Palladium-Gold alloy by means of elevated temperature micropillar compression experiments. All tests were conducted on a stable, displacement-controlled in situ SEM indenter. A series of strain rate jump tests, where the strain rates were varied from 10−4 s−1 up to 10−2 s−1, allowed us to extract strain rate sensitivity and average activation volumes in the order of 8 b3. Repeated load relaxation tests yielded lower activation volumes in the range of 4 b3. From the variation of test temperatures up to 125 °C, we extracted an apparent activation energy of ∼0.77 eV. The possible deformation mechanisms at such extremely small crystallite sizes are discussed within the framework of pertinent literature.