High creep strain rates observed in nanocrystalline α-Fe₂O₃ particles by nanoindentation measurement

Nanocrystalline α-Fe₂O₃ with particle sizes in the range 10–24 nm were produced by mechanical milling of micron-sized α-Fe₂O₃ particles. Microstructures of sintered pellets of cold compacted powder were investigated by electron microscopy. Nanoindentation studies showed the creep strain rates had values of the order of 10⁻⁴ s⁻¹ at room temperature with creep increasing to higher values with increase of particle diameter. This was attributed to grain boundary sliding enhancement due to a piezomagnetic-type effect in the particles. Compressive tests at room temperature carried out on bulk samples with nanosized crystallites also showed large creep strain rate behaviour. The result will be helpful in designing ceramic systems with plastic behaviour at room temperature