Plastic Deformation of Metal Thin Films without Involving Dislocations and Anomalous Production of Point Defects

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Abstract
Evidence for plastic deformation of crystalline metal thin films without involving dislocations is presented. Direct observation of the films during deformation under an electron microscope confirmed the absence of dislocations even for heavy deformation. In fcc metals, including aluminum, deformation leads to the formation of an anomalously high density of vacancy clusters, in the form of stacking fault tetrahedra. These vacancy clusters distribute uniformly when deformation is completed rapidly, but they disappear upon additional deformation, leading to nonuniform distribution of vacancy clusters. Vacancy cluster formation is suppressed when deformation speed is below a certain limit, and this is explained by the escape of deformation-induced vacancies during deformation. Some clusters are formed directly by deformation, and they grow by absorbing deformation-induced vacancies. A new atomistic model for plastic deformation of crystalline metals without involving dislocations is proposed, in which 'glide elements' execute deformation and their reaction produces point defects. Conditions required for operation of the new deformation mechanism is sought in the increase of internal stress under conditions where dislocations tend not to be generated. The possibility of high-speed deformation of bulk materials by this new mechanism is suggested.