Research Article Transition of Dislocation Structures in Severe Plastic DeformationandItsEffectonDissolutioninDislocationEtchant Muhammad Rifai , 1 Ebad Bagherpour , 2 Genki Yamamoto, 3 Motohiro Yuasa, 1 and Hiroyuki Miyamoto 1 1 Department of Mechanical Engineering, Doshisha University, Kyoto, Japan 2 Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran 3 Graduate School of Science and Engineering, Doshisha University, Kyoto, Japan Correspondence should be addressed to Muhammad Rifai; rmuhamma@mail.doshisha.ac.jp Received 27 September 2017; Revised 11 December 2017; Accepted 18 December 2017; Published 30 January 2018 Academic Editor: Alicia E. Ares Copyright©2018MuhammadRifaietal.isisanopenaccessarticledistributedundertheCreativeCommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Transition of dislocation structures in ultrafine-grained copper processed by simple shear extrusion (SSE) and its effects on dissolutionweremanifestedbysimpleimmersiontestsusingamodifiedLivingstondislocationetchant,whichattacksdislocations and grain boundaries selectively. e 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. e weight loss in the immersion tests reflected the variationintheinternalstrain:namely,itincreaseduntileightpassesandthendecreasedwithfurtherextrusiontotwelvepasses. Taking our previous report on microstructural observation into account, it is suggested that variation in the internal strain is causedbyboththevariationindislocationdensityandstructuralchangeofgrainboundariesfromequilibriumtononequilibrium statesorviceversa.Decreaseddislocationdensityandstructuralchangebacktoequilibriumstateofgrainboundariesinveryhigh strainrangebypossiblydynamicrecoveryaspointedoutbyDallaTorrewerevalidatedbyX-rayanddissolutioninthemodified Livingston etchant in addition to the direct observation by TEM reported in our former report. 1.Introduction Grainrefinementtograinsizesbelow1 μmbysevereplastic deformation (SPD) is now well known for improving strengthofbulkmetallicmaterialsforstructuralapplication [1]. Simple shear extrusion (SSE) technique is one of the SPD methods wherein deformation proceeds by pressing the material through a die with a specifically created direct extrusion path [2]. 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, whichmaycauseuniquephysicalandmechanicalproperties [3]. Dislocation density increases to the order of 10 15 m -2 withincreasingnumberofpassesinSPD,formingfinallythe so-called deformation-induced grain boundaries with some dislocations remained inside grains. However, we reported inthepreviousstudythatthesofteningoccurredwithfurther passesafterUFGformationinpurecopperprocessedbySSE, and this softening was considered as a result of a decrease in dislocation density, which was revealed by scanning trans- mission electron microscope (STEM). is decrease in dis- location density after UFG formation may be caused by the dynamic recovery [3–5]. As a classic approach, a dislocation etchant has been used to locate discrete dislocations and its densityinlowplasticstrain[6].However,itwasreportedthat the dissolution rate in a modified solution becomes sensitive todislocationdensityinveryhighrangeandgrainboundaries statewithresidualdislocationsafterSPD,andthedissolution ratewaschangedbytheflushannealinginspitethatgrainsize 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 dislo- cationsandtoexaminethedissolutionbehaviorofUFGcopper. Hindawi Advances in Materials Science and Engineering Volume 2018, Article ID 4254156, 6 pages https://doi.org/10.1155/2018/4254156