Deformation mechanism maps for polycrystalline galena

Abstract

A deformation mechanism map, depicting the fields of stress and temperature in which modes of plastic flow are dominant (i.e. provide the fastest strain rate) has been calculated for polycrystalline, stoichiometric galena for each of two grain sizes; namely, 10 and 10 3 μm. The deformation mechanisms considered were dislocation glide, dislocation creep (i.e. creep involving dislocation climb), Nabarro-Herring creep and Coble creep. During folding and related tectonic deformation in the earth's crust steady-state flow of galena may occur by either dislocation or diffusion creep at very low differential stresses (typically ranging from 100 bars down to 10 −2 bar, or less). The dislocation creep field will be enlarged at the expense of that for diffusion creep, however, if (a) the stress dependence of strain rate for dislocation creep decreases at low stresses and if the grain size is greater than 10 μm, or (b) diffusion creep rates decline at high strains due to the presence of second-phase particles in the grain boundaries. It is probable that dislocation glide will be the dominant deformation mechanism in galena only at low temperatures and fast strain rates and it is unlikely to be the dominant mechanism during folding. Kinking may have some potential as an indicator of these temperatures and strain rates.