Dynamic strain ageing and the boundaries of stable plastic deformation inCu-Mn single crystals

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Abstract
The boundaries of stable plastic deformation, characterized by critical stresses τi(T), are investigated for single crystals of Cu-2 at.% Mn and compared with those of polycrystals. The single crystals were oriented along [100], i.e. for symmetric multiple glide, or for single glide. Strain rate sensitivity was measured between about 300 K and 500 K and for different basic strain rates to deduce activation parameters. The main result is that the form of τi(T) for the [100]-crystals is very similar to that for polycrystals in all respects, whereas it differs appreciably from that for the single-glide crystals. In all cases two different T intervals, labelled α and β, can be distinguished. The activation parameters obtained are the exponent n of the strain rate and the activation energy Ea of the diffusion process inducing jerky flow at τi. Whereas n always equals 1/3, we find for both the single-glide and the [100]-multiple-glide crystals that E α a=0.9eV in the interval α and E β a=1.6eV in the interval β. The values compare well with those for polycrystals and indicate that at least two different diffusion processes occur to induce jerky flow. The differences between the single-glide crystals and the multiple-glide samples are discussed in detail.