ABSTRACT
Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. This chapter reports a hetero-structured lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. The hetero-deformation-induced (HDI) strain hardening is caused by the piling up and accumulation of geometrically necessary dislocations. With increasing tensile strain, dislocation sources in the softer microcrystalline lamellae are activated first. However, the soft lamellae are surrounded and constrained by hard Ultrafine-grained (UFG) lamellae, which are still deforming elastically. In addition to HDI stress, dislocation hardening, which is related to the increase in total dislocation density, should also have contributed to the observed high strain hardening. The HL structure promotes the generation and accumulation of two types of the dislocations during the testing.
