Deformation-induced Nanocomposites

Abstract

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Composite approaches, e.g. with mutually immiscible constituents or including at least one refractory phase, present a viable and maybe even necessary route for stabilizing massive nanostructured materials against detrimental coarsening under thermal and/or mechanical loading conditions. A different way for nanoscaled composite formation is presented by the nanocrystallization of marginally glass-forming amorphous alloys, such as Al-rich alloys with rare earth and transition metal additions. Such composite systems that are stabilized at nanometer-scaled structure sizes due to diffusion limitations have conventionally been processed by supplying thermal energy for initiating the nanocrystal formation. New opportunities for fabricating massive nanocrystalline composites in bulk quantities and with improved microstructures from such alloys might be based on the plastic deformation of the amorphous quenching products, as indicated by the observation of nanocrystallization in shear bands. Here, different deformation methods with largely different strain and pressure levels have been applied on rapidly quenched Al-rich metallic glasses in order to investigate the strain-induced nanocrystal formation. The results indicate e.g. that shear straining under a high pressure and to large strain values can produce uniform nanocrystalline structures in bulk samples, which is essential to their functional performance. Moreover, detailed structure analyses indicate that the amorphous structure of the entire sample volume, and not only the shear band regions, might be affected by the plastic deformation. In addition to the significance concerning the understanding of the deformation of glasses, the results also indicate the applicability of the new processing routes for synthesizing massive, porosity-free nanocrystalline materials.