REVIEWS DOI: 10.1002/adem.200700078 The Innovation Potential of Bulk Nanostructured Materials By Ruslan Z. Valiev , Michael J. Zehetbauer , Yuri Estrin, Heinz Werner Höppel , Yulia Ivanisenko, Horst Hahn, Gerhard Wilde, Hans J. Roven, Xavier Sauvage and Terence G. Langdon* 1. Introduction Over the last decade the development of Bulk Nanostruc- tured Materials (BNM) has become one of the most topical di- rections in modern materials science. [1,2] This interest arises because the development of nanostructures in metals and al- loys paves the way to obtaining unusual properties that are very attractive for various structural and functional applica- tions. [3,4] The use of Severe Plastic Deformation (SPD) pro- cessing techniques [5] has attracted special attention because these techniques provide new opportunities for developing different fabrication technologies for various bulk semi-prod- ucts in the form of sheets, rods, thin foils and wires. Out- standing progress has been made in this area in recent years where new and unusual properties have been demonstrated, including very high strength and ductility, record-breaking fatigue life endurance and superplastic forming capabilities, for a wide range of different metals and alloys. [2–6] The inno- vation potential of this research area is high and accordingly this report focuses on very recent developments demonstrat- ing the potential of using BNM for advanced and functional applications in engineering and medicine. 2. New Trends in BNM Processing and Forming Processing by SPD has now become the established proce- dure for the fabrication of bulk metals, alloys and intermetal- lics having ultrafine-grained (UFG) structures. Furthermore, SPD techniques are now emerging from the domain of labora- tory-scale research into the commercial production of various UFG materials. This change is becoming evident in several ways. Firstly, investigations have extended beyond pure met- als to include metallic alloys, intermetallics and composites so that SPD processing is now under evaluation as a means of enhancing the properties of a very wide range of existing commercial alloys. Secondly, it is apparent that the require- ments for producing nanostructured metals and alloys are be- coming economically feasible. Thirdly, very significant prog- ress has been made in taking SPD products and shaping them into rods, sheets and foils and also in forming articles with complex shapes. Therefore, it is important to examine these new achievements in SPD processing and to highlight some of the more recent developments. Equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) represent the first SPD techniques used for the production of nanostructured metals and alloys possessing submicrometer or even nanometer-sized grains. [7] Since the time of these early experiments, processing regimes and routes have been established for many metallic materials with special emphasis on the procedures required for producing uniform UFG structures and achieving enhanced properties. Recently, numerous alternative techniques for SPD process- ing have also become available including twist extrusion (TE), multi-directional forging (MDF), accumulative roll- bonding (ARB) and cyclic extrusion and compression (CEC): the principles of these various processes were described re- cently. [8] An alternative and attractive processing method is repetitive corrugation and straightening (RCS) which was re- cently developed to process metal sheets and rods in a contin- uous manner. [9] Nevertheless, the SPD techniques in their original designs have some limitations due primarily to the relatively short lengths of the work-pieces so that SPD pro- cessing tends to be a discontinuous process with low produc- tion efficiency and relatively high cost. In addition, the ends ADVANCED ENGINEERING MATERIALS 2007, 9, No. 7 © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 527 The innovation potential is high for bulk nanostructured materials (BNM) produced by methods of se- vere plastic deformation and accordingly this report focuses on very recent developments demonstrat- ing the potential of using BNM for advanced and functional applications in engineering and medicine.