Dislocation cross-slip in fcc solid solution alloys

Abstract

Cross-slip is a fundamental process of screw dislocation motion and plays an important role in the evolution of work hardening and dislocation structuring in metals. Cross-slip has been widely studied in pure FCC metals but rarely in FCC solid solutions. Here, the cross-slip transition path in solid solutions is calculated using atomistic methods for three representative systems of Ni-Al, Cu-Ni and Al-Mg over a range of solute concentrations. Studies using both true random alloys and their corresponding average-alloy counterparts allows for the independent assessment of the roles of (i) fluctuations in the spatial solute distribution in the true random alloy randomness and (ii) average alloy properties such as stacking fault energy. The results show that the solute fluctuations dominate the activation energy barrier, i.e. there are large sample-to-sample variations around the average activation barrier. The variations in activation barrier correlate linearly with the energy difference between the initial and final states. The distribution of this energy difference can be computed analytically in terms of the solute/dislocation interaction energies. Thus, the distribution of cross-slip activation energies can be accurately determined from a parameter-free analytic model. The implications of the statistical distribution of activation energies on the rate of cross-slip in real alloys are then identified.

Tunable stacking fault energies by tailoring local chemical order in CrCoNi medium-entropy alloys

“…We note that a heterogeneous distribution of "local" SFEs may affect the plastic deformation mechanisms, considering the existence of both "weak" and "strong" close-packed atomic planes that is in contrast with conventional crystalline alloys. A similar example can be found in studying the dislocation cross-slip affected by the fluctuations in the spatial solute distribution in random solid solutions(27).The average SFE, isf γ and esf γ in CrCoNi alloys can be quantitatively correlated with the degree of chemical SRO, reflected by the total nonproportional number of local atomic pairs, sum δ ∆ , as shown respectively in Fig. 4B-C.…”

A comparison study of dislocation density, recrystallization and grain growth among nickel, FeNiCo ternary alloy and FeNiCoCrMn high entropy alloy

“…Based on these studies, a reduction of the SFE increases the total dislocation density and the flow stress, and promotes the splitting of a dislocation, which leads to the suppression of recombining the dissociated dislocations and annihilating the dislocations by cross-slip [32,38]. The SFE of materials can be controlled by adjusting alloying elements [41]. Several studies have been reported regarding the effect of alloying elements to Ni-based alloys on the magnitude of the SFE.…”

Influence of the stress state on the cross-slip free energy barrier in Al: An atomistic investigation

“…These atomistic strategies have been used to determine the influence of different chemical species, such as hydrogen [23] or solid solution Al atoms in Ni [24], on the energy barrier for cross-slip. More recently, an atomistically based model has been proposed to compute the energy barrier for cross-slip as a function of the type and volume fraction of solute atoms [25,26]. Additionally, Chen et al [27] studied the effect of vacancy clusters on the cross-slip activation energy in pure Ni, employing the free-end nudged elastic band methodology.…”