Study on Dislocation-Dopant Ions Interaction in Ionic Crystals by the Strain-Rate Cycling Test during the Blaha Effect

Yohichi Kohzuki

doi:10.3390/cryst8010031

Abstract

The interaction between a dislocation and impurities has been investigated by measurements of yield stress and proof stress, micro-hardness tests, direct observations of dislocation, internal friction measurements, or stress relaxation tests so far. A large number of investigations has been carried out by the separation of the flow stress into effective and internal stresses on the basis of the temperature dependence of yield stress, the strain rate dependence of flow stress, and stress relaxation. Nevertheless, it is difficult to investigate the interaction between a dislocation and obstacles during plastic deformation by the mentioned methods. As for the original method which combines strain-rate cycling tests with the Blaha effect measurement, the original method is different from above-mentioned ones and would be possible to clear it up. The strain-rate cycling test during the Blaha effect measurement has successively provided the information on the dislocation motion breaking away from the strain fields around dopant ions with the help of thermal activation, and seems to separate the contributions arising from the interaction between dislocation and the point defects and those from dislocations themselves during plastic deformation of ionic crystals. Such information on dislocation motion in bulk material cannot be obtained by the widely known methods so far. Furthermore, the various deformation characteristics derived from the original method are sensitive to a change in the state of dopant ions in a specimen by heat treatment, e.g., the Gibbs free energy (G0) for overcoming of the strain field around the dopant by a dislocation at absolute zero becomes small for the annealed KCl:Sr2+ single crystal (G0 = 0.26 eV) in comparison with that for the quenched one (G0 = 0.39 eV).

Highlights

The interaction between a dislocation and point defects has been investigated by measurements of yield stress (e.g., [1,2,3,4,5,6,7]) and proof stress (e.g., [8,9]), micro-hardness tests (e.g., [10,11,12,13,14]), direct observations of dislocation (e.g., [15,16,17,18,19,20,21]), internal friction measurements (e.g., [22,23,24,25,26,27]), or stress relaxation tests (e.g., [28,29]) so far
This means that the process of plastic deformation does not affect the decrease of flow stress due to superposition of oscillatory stress
By the original method which combines strain-rate cycling tests with the Blaha effect measurement, the dislocation-Sr2+ ions (I-V dipoles) interaction has been investigated during the plastic deformation of bulk material (KCl:Sr2+ single crystal)

Summary

Introduction

The interaction between a dislocation and point defects has been investigated by measurements of yield stress (e.g., [1,2,3,4,5,6,7]) and proof stress (e.g., [8,9]), micro-hardness tests (e.g., [10,11,12,13,14]), direct observations of dislocation (e.g., [15,16,17,18,19,20,21]), internal friction measurements (e.g., [22,23,24,25,26,27]), or stress relaxation tests (e.g., [28,29]) so far. As for direct observations, electron microscopy provides the information on the interaction between a dislocation

Methods

Results

Conclusion