•Guru Prasad Dinda, Harald Roesner und Gerhard Wilde
Forschungszentrum Karlsruhe, Institute of Nanotechnology, P.O.B. 3640, 76021 Karlsruhe

Repeated cold rolling with intermediate folding 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. In the present work, massive nanocrystalline samples with average grain sizes below 20 nm have been synthesized at ambient temperature from both pure metals (Zr, Ti, Ni etc.) and alloys (NiTi intermetallic compound). The development of the microstructure in dependence of deformation was investigated by X-ray diffraction and scanning and transmission electron microscopy. The development of the nanoscale microstructure during intense deformation - including the early and the late stages of deformation-induced nanocrystal formation - is analyzed in terms of the major thermodynamic and mechanical properties that govern grain refinement and intermixing. In terms of the achievable minimum grain size, repeated folding and rolling presents an attractive low-cost option to obtain nanocrystalline bulk structure that appear to be similar to material obtained by torsion-straining under ultrahigh pressure. This work is supported by the DFG via the Emmy-Noether Program.