Z.S. You

Microstructural evolutions and stability of gradient nano-grained copper under tensile tests and subsequent storage

A gradient nano-grained (GNG) surface layer is produced on a bulk coarse-grained Cu by means of a surface mechanical grinding treatment. Homogeneous grain coarsening induced by mechanical deformation is observed in the GNG Cu layer under tensile tests at both 300 K and 123 K. The concurrent grain coarsening during tensile deformation is proven to be also thermally activated, because the extent of grain coarsening of the GNG Cu layer is less significant at 123 K than at 300 K, although a higher flow stress is achieved at 123 K. During the subsequent storage at 258 K after tensile tests, no obvious change can be found for the grain size in the GNG Cu layer deformed at 300 K. In contrast, widespread abnormal grain coarsening is frequently observed in the GNG Cu layer deformed at 123 K and stored for 100 days, which may be caused by the higher stored energy in the non-equilibrium grain boundary structures.

Kinematic and isotropic strain hardening in copper with highly aligned nanoscale twins

ABSTRACT The kinematic and isotropic strain hardening was investigated in columnar-grained copper with preferentially oriented nanoscale twins deformed at two different strain rates of 5 × 10−5 and 5 × 10−3 s−1. A significant back stress is caused majorly by threading dislocation pile-up and accumulation at the grain boundaries and is strain rate independent. The isotropic hardening associated with an increment in the local effective stress stems from dislocation storage at twin boundaries, and a high strain rate is beneficial for enhancing isotropic strain hardening and tensile ductility. Impact statement Long-range back stress was detected to develop during plastic deformation of nanotwinned structures, majorly caused by pile-up and accumulation of threading dislocations at grain boundary regions. GRAPHICAL ABSTRACT