Short-range order in multicomponent materials

Abstract

The generalized multicomponent short-range order (GM-SRO) parameter has been adapted for the characterization of short-range order within the highly chemically and spatially resolved three-dimensional atomistic images provided by the microscopy technique of atom-probe tomography (APT). It is demonstrated that, despite the experimental limitations of APT, in many cases the GM-SRO results derived from APT data can provide a highly representative description of the atomic scale chemical arrangement in the original specimen. Further, based upon a target set of the GM-SRO parameters, measured from APT experiments, a Monte Carlo algorithm was utilized to simulate statistically equivalent atomistic systems which, unlike APT data, are complete and lattice based. The simulations replicate solute structures that are statistically consistent with other correlation measures such as solute cluster distributions, enable more quantitative characterization of nanostructural phenomena in the original specimen and, significantly, can be incorporated directly into other models and simulations.

A new approach to the analysis of short-range order in alloys using total scattering

“…More complex formulations, such as the generalised multicomponent short-range order (GM-SRO) parameters [30], also exists that can describe interactions of multiple species.…”

Atomically resolved tomography to directly inform simulations for structure–property relationships

“…A key assumption that we make is that ion detection is effectively a stochastic process, and hence, although a significant fraction of atoms are missing from the final reconstruction, this does not affect the values of the measured SRO, that is, the SRO we measure from a data set with 57% detection efficiency is the same as that which would be measured in a hypothetical 100% detection efficiency data set. The validity of this assumption has been previously investigated 28 . It is also well known that in certain analyses can occur a non-stochastic loss of ions due to a combination of preferential evaporation and detector pile-up effects 30,31 , however, this is not expected to be a significant issue for the alloys chosen for this study.…”

“…It has previously been demonstrated that in many cases, the SRO contains sufficient information to accurately predict the identities of the atoms missing due to finite detection in an APT experiment 28 . MC approaches have previously been developed to drive a simulated atomic system to a specific configuration based on using experimentally measured SRO as target parameter 28,43 .…”

“…MC approaches have previously been developed to drive a simulated atomic system to a specific configuration based on using experimentally measured SRO as target parameter 28,43 . Starting at some initial configuration atoms in a lattice, in each step of an SRO-based MC simulation, the relative positions of two atoms are swapped at random.…”

“…1c) are used by the simulation as target values. Atomic positions continue to be swapped at random until the SRO target values have been restored 28 . A critical constraint applied to this simulation is that the positions of the original (experimentally detected) atoms are not moved from their lattice-rectified positions, only the positions of the restored atoms are swapped.…”