Abstract :
[en] The mechanical behaviour of face centered cubic metals is deeply affected when specimen dimensions decrease from a few The millimeters to a few micrometers. At room temperature, a critical thickness (t) to grain size (d) ratio (t/d)c, was previously highlighted, under which the sofiening of mechanical properties became very pronounced both in terms of Hall-Petch relation and work hardening mechanisms. In this work, new experimental results are provided concerning the influence of temperature on this size effect for copper, nickel and Ni-20wt.%Cr, representative of a wide range of deformation mechanisms (i.e. dislocation slip character). It is shown that multicrystalline samples (t/d < (t/d)c) are not deeply affected by an increase in temperature, independently of the planar or wavy character of dislocation glide. For pronounced wavy slip character metals, surface effects in polycrystals (t/d > (t/d)c) are not significant enough to reduce the gap between polycrystal and multierystal mechanical behaviour when the temperature increases. However, a transition from wavy slip to planar glide mechanisms induces a modification ofthe polycrystalline behaviour
which tends tovard multicrystalline one with a moderate increase in temperature. This
work demonstrates that surface effects and grain size influence can be successfully
disassociated for the three studied materials using an analysis supported by the Kooks-
Mecking formalism. All these results are supported by microscopic investigations of
dislocation substructures and compared to numerical simulations using a stress gradient
plasticity model.
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