Local Strain in Tensile Fracture of Metal Foils Estimated from Deformation of Pb Precipitates in Al Matrix

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Abstract
Recently, Kiritani et al. have proposed a new mechanism of plastic deformation without dislocations after conducting a study of tensile fracture of metal foils. The present study treated tensile fracture of Al containing Pb precipitates, and paid special attention to the deformation of precipitates so as to examine local strain and the deformation mechanism. In smooth necking area extending more than 100 w m, precipitates were elongated linearly along the tensile direction by reduction in thickness. Dislocation cell structure was observed all over the specimen, except for sawtooth-shaped thin foils (less than 1 w m in size) formed at the fracture tip, where a large number of vacancy-type defect clusters were observed. Maximum tensile strain was 30-50 in the area that was deformed in conjunction with the dislocation mechanism. In addition, a tensile strain of 20-30 was superposed in the formation of thin foils through the new deformation mechanism. Total tensile strain and the strain rate in the thin foils were estimated at 10 3 and 10 5 s m 1 , respectively. The mode of deformation was discussed on the basis of observation of deformed precipitates; e.g. , a zig-zag pattern on {111} planes observed in the profile of precipitates.