Transition of Dislocation Structures in Severe Plastic Deformation and Its Effect on Dissolution in Dislocation Etchant

Muhammad Rifai,Hiroyuki Miyamoto,Motohiro Yuasa,Ebad Bagherpour,Genki Yamamoto

doi:10.1155/2018/4254156

Muhammad Rifai, Hiroyuki Miyamoto + Show 3 more

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https://doi.org/10.1155/2018/4254156

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Abstract

Transition of dislocation structures in ultrafine-grained copper processed by simple shear extrusion (SSE) and its effects on dissolution were manifested by simple immersion tests using a modified Livingston dislocation etchant, which attacks dislocations and grain boundaries selectively. The SSE process increased the internal strain evaluated by X-ray line broadening analysis until eight passes but decreased it with further extrusion until twelve passes. The weight loss in the immersion tests reflected the variation in the internal strain: namely, it increased until eight passes and then decreased with further extrusion to twelve passes. Taking our previous report on microstructural observation into account, it is suggested that variation in the internal strain is caused by both the variation in dislocation density and structural change of grain boundaries from equilibrium to nonequilibrium states or vice versa. Decreased dislocation density and structural change back to equilibrium state of grain boundaries in very high strain range by possibly dynamic recovery as pointed out by Dalla Torre were validated by X-ray and dissolution in the modified Livingston etchant in addition to the direct observation by TEM reported in our former report.

Highlights

Grain refinement to grain sizes below 1 μm by severe plastic deformation (SPD) is well known for improving strength of bulk metallic materials for structural application [1]
We reported in the previous study that the softening occurred with further passes after ultrafine grain (UFG) formation in pure copper processed by Simple shear extrusion (SSE), and this softening was considered as a result of a decrease in dislocation density, which was revealed by scanning transmission electron microscope (STEM). is decrease in dislocation density after UFG formation may be caused by the dynamic recovery [3,4,5]
It was reported that the dissolution rate in a modified solution becomes sensitive to dislocation density in very high range and grain boundaries state with residual dislocations after SPD, and the dissolution rate was changed by the flush annealing in spite that grain size is not changed [4, 7]. is study was carried out in order to evaluate dislocation density in very high strain range using a modified Livingston etchant which is very sensitive to dislocations and to examine the dissolution behavior of UFG copper

Summary

Introduction

Grain refinement to grain sizes below 1 μm by severe plastic deformation (SPD) is well known for improving strength of bulk metallic materials for structural application [1]. SSE as well as other SPD techniques represented by equal-channel angular pressing (ECAP) and accumulative roll bonding (ARB) produces ultrafine grain (UFG) materials with residual dislocation inside grains, which may cause unique physical and mechanical properties [3]. It was reported that the dissolution rate in a modified solution becomes sensitive to dislocation density in very high range and grain boundaries state with residual dislocations after SPD, and the dissolution rate was changed by the flush annealing in spite that grain size is not changed [4, 7]. Is study was carried out in order to evaluate dislocation density in very high strain range using a modified Livingston etchant which is very sensitive to dislocations and to examine the dissolution behavior of UFG copper It was reported that the dissolution rate in a modified solution becomes sensitive to dislocation density in very high range and grain boundaries state with residual dislocations after SPD, and the dissolution rate was changed by the flush annealing in spite that grain size is not changed [4, 7]. is study was carried out in order to evaluate dislocation density in very high strain range using a modified Livingston etchant which is very sensitive to dislocations and to examine the dissolution behavior of UFG copper

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