Lirong Xiao

Warm rolling at temperatures ranging from 25 °C to 500 °C was conducted on the dual-phase heterostructured low-carbon steel to investigate the effect of deformation temperature on the structural refinement and mechanical properties. Defying our intuition, the grain size and strength of the rolled steels do not deteriorate with the increase in deformation temperature. Warm rolling at 300 °C produces a much finer lamellar structure and higher strength than steels rolled at both room temperature and elevated temperature. It is supposed that the enhanced interactions between carbon atoms and defects (interfaces and dislocations) at 300 °C promote dislocation accumulation and stabilize the nanostructure, thus helping with producing an extremely finer structure and higher strength than other temperatures.

Commercial‐purity aluminum with 99.7% purity is processed by rotational accelerated shot peening (RASP) and cold‐rolling. RASP samples are rolled at room temperature to a thickness reduction of 20% and 30%, for the purpose of surface roughness reduction and strengthening. Detailed microstructural characterization and hardness tests reveal that cold‐rolling cause grain growth at the surfaces of RASP samples from ≈472 to ≈1000 nm. Moderate cold‐rolling is effective in smoothing the surface of RASP samples, while improving strength and maintaining ductility. However, cold‐rolling to more than 30% thickness reduction eventually diminishes the gradient nanostructure. During cold‐rolling of RASP samples, a transition zone with strong strain incompatibility is noticed by a sharp rise in hardness at some point of the hardness‐distribution curve from the surface to the core of the sample. This transition zone is a result of quick generation of geometrically necessary dislocations. Although the transition zone with strong strain incompatibility is short‐lived, it is anticipated to be common among gradient‐nanostructured materials under cold‐rolling condition.