Dislocation avalanche mechanism in slowly compressed high entropy alloy nanopillars

Yang Hu,Peter K Liaw,Li Shu,Jian-Min Zuo,Wei Guo,Karin A Dahmen,Qun Yang

doi:10.1038/s42005-018-0062-z

Abstract

Crystals deform by the intermittent multiplication and slip avalanches of dislocations. While dislocation multiplication is well-understood, how the avalanches form, however, is not clear, and the lack of insight in general has contributed to “a mass of details and controversy” about crystal plasticity. Here, we follow the development of dislocation avalanches in the compressed nanopillars of a high entropy alloy, Al0.1CoCrFeNi, using direct electron imaging and precise mechanical measurements. Results show that the avalanche starts with dislocation accumulations and the formation of dislocation bands. Dislocation pileups form in front of the dislocation bands, whose giveaway trigs the avalanche, like the opening of a floodgate. The size of dislocation avalanches ranges from few to 102 nm in the nanopillars, with the power-law distribution similar to earthquakes. Thus, our study identifies the dislocation interaction mechanism for large crystal slips, and provides critical insights into the deformation of high entropy alloys.

Highlights

Crystals deform by the intermittent multiplication and slip avalanches of dislocations
How intermittent dislocation activities stem from complex dislocation patterns, how these activities impact the dislocation pattern formation, and how this trend leads to crystal slip, are all unresolved critical questions[5,13,14]
The composition and structure of the high entropy alloys (HEAs) sample were characterized by atom probe tomography (APT), electron imaging, and diffraction

Summary

Introduction

Crystals deform by the intermittent multiplication and slip avalanches of dislocations. Our study identifies the dislocation interaction mechanism for large crystal slips, and provides critical insights into the deformation of high entropy alloys. How intermittent dislocation activities stem from complex dislocation patterns, how these activities impact the dislocation pattern formation, and how this trend leads to crystal slip, are all unresolved critical questions[5,13,14]. To start addressing these questions, we followed the dislocation motions inside a slowly compressed nanopillars using the brightfield (BF) TEM, while simultaneously we measured the load and displacement using a pico-indenter (model PI 95, Hysitron, MN, USA). The avalanche mechanism that we identified is based on interactions between the dislocation pileup and the dislocation band, and between the pileup and dislocation pinning centers

Methods

Results

Conclusion