Nanomaterials have been produced in the past mainly by bottom-up methods: by producing single or clusters of nanocrystals by inert gas condensation, ball milling and electrodeposition, or by thermal growth from the amorphous state. In all cases, the sample size has been limited to just a few millimeters. This fact has limited their application as functional materials so far, especially for commercial use.
Over the past decade, the severe-plastic-deformation (SPD) technique has proven to be the most-promising top-down processing route. It allows bulk, dense, nanostructured samples of a size far beyond 10 mm in each dimension. The most-commonly used SPD method, equal channel angular pressing (ECAP), has the highest potential in this respect.
Bulk nanomagnets and nanostructured shape memory alloys processed by SPD represent activities of the recently established Austrian National Research Network ‘High-Performance Bulk Nanocrystalline Materials’ of the Austrian Science Fund. This network comprises five research institutions from Vienna, Leoben and Graz and includes the realization of massive nanomaterials with functional properties.
Now, in new work, a team of researchers from these institutions give different examples of functional properties of nanomaterials. They present promising results of reaching functional properties in SPD-processed bulk nanocrystalline magnetic alloys, bulk shape memory nanoalloys, as well as nanometals and alloys for hydrogen storage. The report also shows problems with other functional properties, like those of thermoelectricity, occurring in non-metallic nanomaterials.
The presented examples expose that at present bulk nanocrystalline materials with an enhanced shape memory effect and hydrogen-storage properties can be achieved already. They possess the highest chance for commercial use. The potential of bulk shape memory nanoalloys effects for applications such as for new medical devices is very large. Bulk nanomaterials for hydrogen storage seems to possess the highest potential to be used together with fuel cells for the generation of electric power in a clean, inexpensive, safe and efficient manner.
For SPD nanomagnets and especially SPD thermoelectrics, however, further basic research and development is required.