Evidence for plastic deformation of crystalline metal thin foils without dislocations is presented. Direct observation during deformation under an electron microscope confirmed the absence of the operation 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. The dependency of vacancy cluster formation on temperature and deformation speed indicates that the clusters are formed by the aggregation of deformation-induced vacancies. Conditions required for the absence of the dislocation mechanism are explained, and a new atomistic model for plastic deformation of crystalline metals is proposed.
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