Local-environment dependence of stacking fault energies in concentrated solid-solution alloys

Shijun Zhao,Yuri Osetsky,Yanwen Zhang,G Malcolm Stocks

doi:10.1038/s41524-019-0150-y

Abstract

Concentrated solid-solution alloys (CSAs) based on 3d transition metals have demonstrated extraordinary mechanical properties and radiation resistance associated with their low stacking fault energies (SFEs). Owing to the intrinsic disorder, SFEs in CSAs exhibit distributions depending on local atomic configurations. In this work, the distribution of SFEs in equiatomic CSAs of NiCo, NiFe, and NiCoCr are investigated based on empirical potential and first-principles calculations. We show that the calculated distribution of SFEs in chemically disordered CSAs depends on the stacking fault area using empirical potential calculations. Based on electronic structure calculations, we find that local variations of SFEs in CSAs correlate with the charge density redistribution in the stacking fault region. We further propose a bond breaking and forming model to understand and predict the SFEs in CSAs based on the local structure alone. It is shown that the perturbation induced by a stacking fault is localized in the first-nearest planes for NiCo, but extends up to the third nearest planes for NiFe and NiCoCr because of partially filled d electrons in Fe and Cr.

Highlights

As the accessible stacking fault size is limited both in experimental observations and theoretical atomistic modeling, a value of stacking fault energies (SFEs) for concentrated solid-solution alloys (CSAs) estimated by any technique will depend on local environments, and variations in SFE values are related to the area considered
We report distributions of SFEs in equiatomic CSAs of NiCo, NiFe, and NiCoCr using static simulations based on both empirical potential and first-principles density functional theory (DFT) calculations
We first show the dependence of SFE distribution in CSAs on the stacking fault area

Summary

INTRODUCTION

Single-phase concentrated solid-solution alloys (CSAs) with two or more multiple principal elements situated on a simple lattice have demonstrated remarkable mechanical properties and irradiation resistance.[1,2,3,4,5,6] In particular, several Ni-based face-centered cubic (fcc) CSAs composed of 3d transition metal elements are found to exhibit excellent fracture toughness and damage tolerance under tensile stress at cryogenic temperature.[2,7] It has been shown experimentally that the high strength of CSAs is closely related to the change in deformation mechanisms from conventional dislocation glide to twining with decreasing temperature.[2]. In pure metals and dilute alloys, the SFE is characterized by a single value; in CSAs, it should be regarded as a spatially localized property that affects dislocation properties within a certain range.[8,16] As the accessible stacking fault size is limited both in experimental observations and theoretical atomistic modeling, a value of SFE for CSAs estimated by any technique will depend on local environments, and variations in SFE values are related to the area considered. The relation between a certain SFE and its local environment is of particular interest as it can predict stability of local structures and/or deformation mechanisms Such a relationship should help to understand local dislocation properties in CSAs when short-range order develops or inhomogeneous composition is present, as already found in some CSAs.[17,18] The established dependence of SFEs on local chemical environment may provide guidance for tuning alloy properties of CSAs by tailoring their chemical fluctuations. The mean SFE value is not much influenced by the stacking fault area, suggesting a possibility of estimating the SFE limit for an infinite stacking fault area using a finite supercell as long as the statistical

RESULTS AND DISCUSSION

METHODS

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