Equilibrium versus non-equilibrium stacking fault widths in NiCoCr

C. Baruffi (1) , M. Ghazisaeidi (2) , David Rodney (3) , W.A. Curtin (1, 4)

1 EPFL - Ecole Polytechnique Fédérale de Lausanne
2 Department of Materials Science and Engineering [Colombus]
3 iLM - MMCI - iLM - Modélisation de la matière condensée et des interfaces
4 Brown Engineering - School of Engineering

First principles calculations in the NiCoCr medium-entropy alloy predict a negative stacking fault energy (SFE) at T=0 K, implying an infinite Shockley partial dissociation distance. Many experiments at room temperature (RT) show however a finite dissociation. This discrepancy has been suggested due to solute strengthening that prevents the partial separation. Here, atomistic simulations in a model NiCoCr alloy having a negative SFE show that solute strengthening can limit partial separation at T=0 K but, the solute-induced barriers are easily overcome at RT and time scales of only 1 ns. Under experimental conditions (time scales of hundreds of seconds and longer), solute pinning is therefore insufficient to limit dissociation. Finite partial separations are thus presumably due to a positive stacking fault free energy at RT or short-range-order effects. It is argued here that the former is more likely than the latter.

Mots clés: Molecular dynamics (MD); ENERGIES; 1ST-PRINCIPLES; DISLOCATIONS; Stacking fault energy; Plasticity; Metal and alloys; Dislocation mobility

Domaines: Physique [physics]

C. Baruffi, M. Ghazisaeidi, David Rodney, W.A. Curtin. Equilibrium versus non-equilibrium stacking fault widths in NiCoCr. Scripta Materialia, 2023, 235, pp.115536. ⟨10.1016/j.scriptamat.2023.115536⟩. ⟨hal-04173099⟩