Crystal Orientation Dependence of the Portevin–Le Chatelier Effect in Instrumented Indentation: A Case Study in Twinning-Induced Plasticity Steels

Xiuxing Peng,Zhiyuan Liang,Wei Xu,Lingyu Wang

doi:10.3390/met12030439

Xiuxing Peng, Zhiyuan Liang + Show 2 more

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https://doi.org/10.3390/met12030439

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Abstract

Instrumented indentation can be effectively used to investigate the Portevin–Le Chatelier (PLC) effect at small scales. It has been shown that the PLC effect in single crystals may depend on the crystal orientation, yet the underlying mechanism is unclear. Here, the orientation dependence of the PLC effect was systematically studied by conducting instrumented indentation tests in the [001]-, [101]- and [111]-oriented grains of a polycrystalline twinning-induced plasticity steel. It is found that the crystal orientation does not affect the PLC effect at relatively high indentation strain rates. In contrast, there is a strong orientation dependence at lower rates, with enhanced difficulty in the formation of serrations in the order of the [001], [111] and [101] orientations. This finding contradicts the previous proposals of the orientation effects, which are associated with the dislocation waiting time. On the basis of both the orientation and rate effects observed here, we proposed that the crystal orientation influences the occurrence of serrations in instrumented indentation by affecting the number of activated slip systems and, therefore, the probability of finding sufficient dislocation sources to accommodate the plastic avalanche.

Highlights

Academic Editor: Eric HugThe Portevin–Le Chatelier (PLC) effect is a phenomenon of plastic instability that manifested as serrations on the stress–strain curves and the formation of PLC bands [1,2]
This finding contradicts the previous proposals of the orientation effects that are associated with the dislocation waiting time
We proposed that the crystal orientation influences the occurrence of serrations in instrumented indentation by affecting the number of activated slip systems and, the probability of finding sufficient dislocation sources to accommodate the plastic avalanche

Summary

Introduction

The Portevin–Le Chatelier (PLC) effect is a phenomenon of plastic instability that manifested as serrations on the stress–strain curves and the formation of PLC bands [1,2]. It is generally accepted that the PLC effect results from negative strain rate sensitivity (nSRS), which is caused by dynamic strain aging (DSA) [3,4]. When dislocations encounter local obstacles and stop temporarily, solute atoms can diffuse to the dislocation cores and pin the dislocations. The dislocations cannot move unless the applied stress is sufficiently high for them to break from obstacles. DSA is the process of dislocations moving and being pinned by solute atoms when they are temporarily arrested [5,6]. DSA occurs when the dislocation waiting time is longer than the solute diffusion time [4,7]

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