Coupled Strengthening Effects by Lattice Distortion, Local Chemical Ordering, and Nanoprecipitates in Medium-Entropy Alloys

Xiaolei Wu,Wenqiang Cheng,Fuping Yuan

doi:10.3389/fmats.2021.767795

Abstract

Extraordinary mechanical properties can be achieved in high-entropy alloys (HEAs) or medium-entropy alloys (MEAs) with nanoprecipitates. In the present study, the extra coupled strengthening effects by lattice distortion, local chemical ordering, and nanoprecipitates in the HEAs and MEAs with nanoprecipitates have been systematically investigated by large-scale molecular dynamics simulations. The moving of the dislocation can be slowed down, and the dislocation line shows a wavy configuration due to lattice distortion and local chemical ordering, resulting in strengthening. The degree of the wavy configuration increases and the sliding velocity of the dislocation decreases with increasing degrees of local chemical ordering. It is clearly indicated that the dislocation moves via nanoscale segment detrapping mechanism due to the effects of lattice distortion and local chemical ordering, resulting in roughened dislocation pathways for strengthening. The activated nanoscale segments are observed to be easier to detrap from the regions with stronger Co-Cr local chemical ordering and then propagate into the regions without such chemical ordering. These moving characteristics of the dislocation can delay the unpinning process from nanoprecipitates; thus, extra coupled strengthening effect has been revealed in the HEAs and MEAs with nanoprecipitates compared to pure Orowan’s strengthening.

Highlights

INTRODUCTIONHigh-entropy alloys (HEAs) (Yeh et al, 2004; Cantor et al, 2004; Gludovatz et al, 2014; Schuh et al, 2015; George et al, 2020; LaRosa et al, 2019; Li et al, 2016; Lei et al, 2018; Jo et al, 2017; George et al, 2019; Shi et al, 2019) and/or medium-entropy alloys (MEAs) (Gludovatz et al, 2016; Miao et al, 2017; Yang M. et al, 2018a; Ma et al, 2018; Yang M. et al, 2019a; Wu et al, 2020; Sohn et al, 2019; Slone et al, 2019; Ding et al, 2018) are solid solution alloys consisting of three or more elements generally with equal atomic fraction
The original contributions presented in the study are included in the article/Supplementary Material, and further inquiries can be directed to the corresponding author
All authors contributed to manuscript revision, read, and approved the submitted version

Summary

INTRODUCTION

High-entropy alloys (HEAs) (Yeh et al, 2004; Cantor et al, 2004; Gludovatz et al, 2014; Schuh et al, 2015; George et al, 2020; LaRosa et al, 2019; Li et al, 2016; Lei et al, 2018; Jo et al, 2017; George et al, 2019; Shi et al, 2019) and/or medium-entropy alloys (MEAs) (Gludovatz et al, 2016; Miao et al, 2017; Yang M. et al, 2018a; Ma et al, 2018; Yang M. et al, 2019a; Wu et al, 2020; Sohn et al, 2019; Slone et al, 2019; Ding et al, 2018) are solid solution alloys consisting of three or more elements generally with equal atomic fraction. These two strengthening effects might be coupled, and extra strengthening/hardening could be obtained due to this coupled effect, while the deformation mechanisms for this possible coupled effect are still unclear In this regard, large-scale MD simulations have been conducted in the present study to investigate the a/2 < 110> edge dislocation sliding behaviors in a CoCrNi MEA with a wide variety of local chemical ordering and with/without nanoprecipitates. For the samples without nanoprecipitates, the A-atom potential (Sadigh et al, 2012) was used to differentiate and identify the effects of lattice distortion and local chemical ordering on the strengthening/hardening, besides the regular EAM potential. In which gray color is for fcc atoms, red color is for hcp atoms (SF), and green color is for dislocation cores and free boundary atoms

RESULTS AND DISCUSSIONS

SUMMARY AND CONCLUDING REMARKS

DATA AVAILABILITY STATEMENT