Materials Science Forum, Vol.503-504, 31-36, 2006
Local investigations of the mechanical properties of ultrafine grained metals by nanoindentations
The mechanical properties of ultrafine-grained metals processed by equal channel angular pressing is investigated by nano indentations in comparison with measurements on nanocrystalline nickel with a grain size between 20 and 400 nm produced by pulsed electrodeposition. Besides hardness and Young's modulus measurements, the nanoindentation method allows also controlled experiments on the strain rate sensitivity, which are discussed in detail in this paper. Nanoindentation measurements can be performed at indentation strain rates between 10(-3) s(-1) and 0.1 s(-1). Nanocrystalline and ultrafine-grained fee metals as Al and Ni show a significant strain rate sensitivity at room temperature in comparison with conventional grain sized materials. In ultrafine-grained bee Fe the strain rate sensitivity does not change significantly after severe plastic deformation. Inelastic effects are found during repeated unloading-loading experiments in nano indentations.
Keywords:ultrafine-grained metals;nanocrystalline metals;pulsed electrodeposition;nanoindentations;strain rate sensitivity