Evolution in Microstructures and Mechanical Properties of Pure Copper Subjected to Severe Plastic Deformation
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Evolution in Microstructures and Mechanical Properties of Pure Copper Subjected to Severe Plastic Deformation Mingya Zhang1 · Li Liu1 · Shan Liang1 · Jinghui Li1 Received: 24 April 2019 / Accepted: 23 July 2019 © The Korean Institute of Metals and Materials 2019
Abstract Considering the great advantage of improving the pressing speed in reducing the number of repeated deformation passes and grain size, high-speed equal channel angular pressing (ECAP) technology has been applied to achieve the perfect distribution of grain size in a sample volume of pure copper. The microstructures and mechanical properties of pure copper suffering ECAP are investigated. The results show that the well refined grains are obtained through three stages, during which the grain reorientation and recrystallization occurs. After ECAP, the volume fraction of high-angle grain boundaries is reduced, but shows an obvious increase in the population for high-pass extruded sample. Besides, ECAP can significantly increase the proportion of the special boundaries probably through the transformation from annealing twins to deformation twins. The tensile strength of ECAP-ed sample greatly increased to 1.87 times larger than that of the annealed bar, and then improved slowly regardless of increasing strain. The relationship between strength and grain size still obeyed Hall–Petch formula. The cloud maps of microhardness distribution illustrated that the hardness is severely improved after the first three passes, but leveled off after that. Besides, the cloud maps also present the moderate inhomogeneity of microhardness with higher values in the edge and lower values towards the center. Keywords Severe plastic deformation · Pure copper · Microstructure · Mechanical property
1 Introduction Producing ultrafine grained (UFG) or nanostructural materials is perspective due to their unique combination of constructional and functional properties, such as the high strength, fatigue resistance combined with good ductility, as well as excellent superplasticity and even corrosion resistance compared with common macrocrystalline analogs [1–5]. Among various methods to produce these materials, severe plastic deformation (SPD) technologies are of more efficiency to fabricate UFG or even bulk nanostructural materials avoiding contamination or porosity. Equal channel angular pressing (ECAP) as the most widespread SPD method is first proposed by a team of Segal [6] and subsequently developed by Valiev and his coworkers [1, 7]. As one of the most widely used electric material, pure copper is short of high-strength. ECAP can solve this * Jinghui Li [email protected] 1
School of Metallurgical Engineering, Anhui University of Technology, Ma’anshan 243002, China
problem well in this respect. Dalla Torre et al. [8] employed ECAP to fabricate UFG pure coppers yielding the size of 200 nm and illustrated that the maximum value of the strength and hardness is achieved after four passes. Han et al. [9] carried out intermediate annealing and cyclic ECAP on pure copper. This
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