Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy

G. Laplanche (1) , J. Bonneville (2) , C. Varvenne (3) , W. A. Curtin (4) , E. P. George (5, 6)

1 RUB - Ruhr University Bochum = Ruhr-Universität Bochum
2 PDP - Physique des Défauts et de la Plasticité [Institut Pprime]
3 CINaM - Centre Interdisciplinaire de Nanoscience de Marseille
4 EPFL - Ecole Polytechnique Fédérale de Lausanne
5 ORNL - Oak Ridge National Laboratory [Oak Ridge]
6 The University of Tennessee [Knoxville]

To reveal the operating mechanisms of plastic deformation in an FCC high-entropy alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, sigma(y), the activation volume varies from similar to 60 b(3) at 77 K to similar to 360 b(3) at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with sigma - sigma(y) (Haasen plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-strengthened alloy. These results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms.

Mots clés: High-entropy alloys; CoCrFeMnNi plastic deformation mechanisms; Stress relaxation; Dislocations; Activation volume

Domaines: Mécanique des matériaux [physics.class-ph]

G. Laplanche, J. Bonneville, C. Varvenne, W. A. Curtin, E. P. George. Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy. Acta Materialia, 2018, 143, pp.257-264. ⟨10.1016/j.actamat.2017.10.014⟩. ⟨hal-01688044⟩