Comparison of Structure and Properties of Nanomaterials Processed by Ball Milling and High Pressure Torsion

Cu nanomaterials processed by Ball Milling (BM) and High Pressure Torsion (HPT) were investigated by microhardness, multiple whole X-ray profile analysis, and differential scanning calorimetry (DSC). The strength of BM samples and its dependence on milling time (equivalent to strain) is much higher than that of HPT samples, which can be related to the huge difference between coherent domain sizes (CSD) after BM and HPT, respectively. Therefore, very high values of fatigue strength in BM samples can be expected. The stored energy of BM samples derived from DSC again is much higher than those of HPT, but strongly decreases with increasing milling time finally reaching the level of HPT. Since neither dislocation density nor CSD can account for this behaviour, the extra high energy stored in BM samples is attributed to a very high concentration of deformation induced vacancy type defects which appear to gradually anneal with increasing milling time.