Synthesis of Bulk Nanocrystalline Materials and Bulk Metallic Glasses by Repeated Cold Rolling and Folding (RCR)

Repeated cold rolling with intermediate folding (RCR) represents a technique to obtain severe plastic deformation that avoids excessive heating at the internal interfaces and that proceeds without the simultaneous action of a high pressure in the range of several GPa. Aside from the opportunity to obtain amorphous bulk samples, the processing pathway also allows for synthesizing dense, bulk nanocrystalline materials. The sequential combination of different processing routes that drive a material to a different extent -, with different rates - and by different means from thermodynamic equilibrium present new and attractive processing opportunities to obtain bulk nanocrystalline or massive ultrafine grained materials that are widely unexplored. Here, an overview is presented concerning the sequential application of different deformation methods with largely different strain and pressure levels. The basic underlying mechanisms that can lead to ultrafine grained or nanocrystalline microstructures for pure metals or to two-phase nanocomposites or bulk metallic glasses for alloys are discussed and the current state of nanostructure control is highlighted by selected examples.