Cross-slip and fatigue in metals at low temperatures

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Abstract
The mutual annihilation of jogged screw dislocations approaching one another on non-parallel slip planes is shown to give rise to a type of recovery which accounts satisfactorily for the pronounced decline in the rate of work-hardening observed in f.c.c. metal crystals above a certain shear stress, frequently denoted by τIII(T). The relation τIII = (τIII)o[1 - (mkT/Q)], deduced from the model, where (τIII)a = τIII(0), m =30 and Q the energy of vacancy formation, agrees well with the experimental data for aluminium, copper, gold and nickel up to about 0·15 T m, where T m (°k) is the temperature of melting. It is suggested that the heat evolved during such dislocation annihilations facilitates the clustering of slip into bands observed at stresses above r III by catalyzing further destructive interactions, and that condensation of vacancies formed in the process of cross-slip provides the crack nuclei in slip clusters from which fatigue fractures spread. The temperature dependence of the fatigue limit appears to be the same at that of τIII.

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