Work-hardening and work-softening of face-centred cubic metal crystals

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Abstract
The present paper investigates by experiment and theory the mechanisms governing work-hardening, work-softening and slipband formation in face-centred cubic metals. The rapid hardening stage (stage II) of the stress-strain curve is investigated by flow-stress measurements at different temperatures, combined tensile and torsion experiments, and by the observation of the length of slip lines as a function of prestrain. Stage III of the stress-strain curve and the work-softening phenomena associated with it are investigated with the electron microscope, showing that the principal surface patterns (slip bands, fragmentation) are due to cross slip. It is argued that in stage II the slip distance is decreased continually by the formation of Lomer-Cottrell dislocations. This also accounts for various observations on the end of the easy glide region. The temperature dependence of work-hardening in stage III is caused by screw dislocations circumventing the sessile Lomer-Cottrell dislocations by cross dip. The mechanisms through which cross slip causes glide band formation and fragmentation are discussed in some detail.

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