The Effects of Grain Size on Dislocations organization and Internal Stresses developed under Tensile Loading in f.c.c. metals

Xavier Feaugas (1) , Haddou Hakim (2)

1 LEMMA - Laboratoire d'Etude des Matériaux en Milieux Agressifs
2 Roberval - Roberval

The relation between deformation and dislocation properties has been studied for pure polycrystalline nickel and austenitic stainless steel AISI 316L in stage III. Special care was taken to study statistically the effects of the grain size and grain orientation on dislocations densities and distribution. It is shown that the nature of dislocations cells depends on the grain size and crystallographic orientation. The dimensional parameters which depend on the grain size, i.e. the inter-boundary spacing (Λ) and the boundary thickness (e) define three domains of crystallographic orientation and depend on the grain size. Scaling hypotheses reveal two physical mechanisms which, at this level of plastic strain, are correlated to a specific value of the noise, associated with the distribution functions. A similitude between structural parameters and dislocation densities in each phase (walls and inter-walls spacing) is identified and discussed in terms of kinetic equations describing dislocation density evolutions and of fluctuations of certain physical parameters. This similitude provides a physical signification of the scaling distribution obtained on Λ and e in terms of a stochastic approach of dislocation distribution. The origin of Hall-Petch behaviour observed at large strain is interpreted in terms of an interaction between inter-granular and intra-granular long-range internal stresses, which depends on the grain size. We conclude that, at high strain, the Hall & Petch phenomenological relation is a consequence of plastic strain history and of strain gradient in grains. From this last point naturally arises a length scale which depends on stacking fault energy.

Mots clés: Physical Sciences

Domaines: Sciences de l'ingénieur [physics]

Xavier Feaugas, Haddou Hakim. The Effects of Grain Size on Dislocations organization and Internal Stresses developed under Tensile Loading in f.c.c. metals. Philosophical Magazine, 2007, 87 (07), pp.989-1018. ⟨10.1080/14786430601019441⟩. ⟨hal-00513785⟩