Affiliation: | a The Oarai Branch, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313, Japan b Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan c Academic Frontier Research Center for Ultra-high-speed Plastic Deformation, Hiroshima Institute of Technology, Hiroshima 731-5193, Japan |
Abstract: | Vacancies and vacancy clusters in Ni, Cu, and Fe induced by high- and low-speed deformations are studied systematically by positron annihilation techniques and are compared with those induced by the conventional-rolling. To clarify the nature of the defects, the experimental results are compared with our superimposed-atomic-charge calculations of the positron lifetimes in the vacancy clusters as a function of their size. It is found that the deformation-induced defects in the fcc and bcc metals are significantly distinct. In the fcc metals of Ni and Cu, monovacancies with high number densities are induced by the high- and low-speed deformations and by heavy conventional-rolling (>10% in Ni and >40% in Cu). Vacancy clusters are observed after the high- and low-speed deformation for Ni and after the conventional-rolling for Cu. On the contrary, dislocations and vacancy clusters are introduced in bcc Fe regardless of the type or degree of deformation. |