Plastic deformation of bcc metal thin foils without dislocation

Heavy plastic deformation of fee metal thin foils to fracture has been found recently to proceed without involving dislocations, and it results in the formation of high density of vacancy clusters. Thin foil specimens of bee metals such as V and Mo were plastically deformed to fracture in in situ elongation experiments under an electron microscope. Morphology of thinning and fracture was found to be similar to fee metals, and no dislocation was observed during heavy deformation. Electron diffraction analysis at the tip of a crack during deformation confirmed a large elastic deformation of up to 5%. Unlike in fee metal thin foil specimens, point defect clusters were not observed near fractured tips. This difference is attributed to the difference in vacancy reaction, though the deformation in bee metals without dislocation most likely does produce vacancies. (C) 2002 Published by Elsevier Science B.V.