Micro-deformation evolutions of the constituent phases in duplex stainless steel during cyclic nanoindentation

Yuan-Yuan Cui,Yun-Fei Jia,Fu-Zhen Xuan

doi:10.1038/s41598-018-24589-4

Yuan-Yuan Cui, Yun-Fei Jia + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-24589-4

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Abstract

Cyclic elastoplastic deformation behaviors of austenite phase and ferrite phase in a duplex stainless steel were investigate by load-controlled cyclic nanoindentation with a Berkovich indenter. During the tests, the maximum penetration depth per cycle increased rapidly with cycle number at transient state, and reached stable at quasi-steady state. Plastic dissipated energy was quantitatively proved to be the driving force for the propagation of deformation zones during cyclic nanoindentation tests. Transmission electron microscopy combined with FIB was used to reveal the deformation mechanisms of both phases underneath indents with cycles. After quasi-static single loading, nucleation and concentration of dislocations were observed in both austenite phase and ferrite phase under the indenter. After cyclic loading, dislocations propagated to further regions in both phases. Besides, slip bands were generated within single nanoindentation and propagated during the subsequent cyclic nanoindentation. The sizes of the deformation regions for both phases under the indents after cyclic indentation observed by TEM were consistent with those calculated by the expansion model of spherical cavity.

Highlights

Duplex stainless steels (DSS) are composed of approximately equal amounts of two constituents, such as austenite phase and ferrite phase, or ferrite phase and martensite phase
In order to figure out the deformation mechanisms of materials under the indentation pit, some researchers have used microscopy observation, such as Scanning Probe Microscope (SPM), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM), combined with sample preparation technology of Focused Ion Beam (FIB) milling
The present study offers a better understanding of cyclic deformation behaviors and mechanisms of austenite phase and ferrite phase at the micro scale

Summary

Introduction

Duplex stainless steels (DSS) are composed of approximately equal amounts of two constituents, such as austenite phase and ferrite phase, or ferrite phase and martensite phase. To have a deeper understanding of the mechanical properties of DSS, it is necessary to investigate the local deformation behaviors of each constituent phase at the scale of crystalline. To our knowledge, few studies focused on the cyclic indentation behaviors of the constitute phase of duplex stainless steel and on the deformation mechanisms evolution underneath the indent with indentation cycles. The load-controlled cyclic indentation tests on the respective phase of an austenite/ferrite duplex stainless steel were performed to investigate the dynamic deformation behaviors of austenite phase and ferrite phase, and TEM observations combined with FIB milling technology were used to reveal the deformation mechanisms of the respective phases under indentations with cycles. The present study offers a better understanding of cyclic deformation behaviors and mechanisms of austenite phase and ferrite phase at the micro scale

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