Available online at www.sciencedirect.com ScienceDirect JMST ELSEVIER J.Mater..Sci.Technol..,2011,27(8).673-679. www.JMST.org Quantifying the Microstructures of Pure Cu Subjected to Dynamic Plastic Deformation at Cryogenic Temperature F.Yan,H.W.Zhang',N.R.Tao and K.Lu Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016.China Manuscript received April 12,2011,in revised form May 30,2011] A pure Cu(99.995 wt%)has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1.Three types of microstructures that are related to dislocation slip,twinning and shear banding have been quantitatively characterized by transmission electron microscopy (TEM)assisted by convergent beam electron diffraction (CBED)analysis.Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries(<15)that are spaced in the nanometer scale,whereas most deformation twins are deviated from the perfect >3 coincidence(60/<111>)up to the maximum angle of 9.The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates,and allowed a quantitative analysis of the flow stress-structural parameter relationship. KEY WORDS:Quantitative structural characterization;Cu;Dynamic plastic deformation;Trans- mission electron microscopy;Convergent beam electron diffraction 1.Introduction parameters and to set up the relationship between flow stress and these parameters. There is a current interest in the microstructural The material chosen for investigation was high- refinement by plastic deformation at high strain rates purity Cu (99.995 wt%)processed by dynamic plas- and low temperature-4.Generally,three types of tic deformation (DPD)at cryogenic temperature to deformation mechanisms are activated in metals with a strain of 2.1.TEM (transmission electron mi- low stacking fault energy(SFE)such as Cu and Cu- croscopy)based CBED (convergent beam electron alloy,i.e.dislocation slip,twinning and shear banding diffraction)technique was used to quantify the mi- (SB)12).The microstructural refinement induced by crostructural parameters.The structural characteris- these three mechanisms is different,with the smallest tic as well as the strengthening mechanism has been value(47 nm)by twinning,followed by SB(75 nm) discussed and dislocation slip (121 nm)1.However,detailed 2.Experimental microstructural characters including the structural parameters such as boundary misorientation angles. fraction of high or low angle boundaries and the dis- High-purity polycrystalline Cu (99.995 wt%)in location density between and in the boundaries are the form of cylinder (9 mm in diameter and 12 mm in lacking,whereas these parameters play a crucial role thickness)was subjected to DPD at cryogenic temper- ature (liquid nitrogen),which is denoted as LN-DPD in understanding the deformation mechanism and the structure-strength relationship.It is thus the objec- Cu.Prior to DPD,the sample was annealed at 973 K for 2 h in order to remove the residual stress and to tive of the present study to quantify the structural obtain the fully-recrystallized structures.The start- ing material is composed of equiaxed recrystallized Corresponding author.Tel.:+86 24 23971890;E-mail ad- grains with an average size of 200 um and a fraction dress:hwzhang@imr.ac.cn (H.W.Zhang).J. Mater. Sci. Technol., 2011, 27(8), 673-679. Quantifying the Microstructures of Pure Cu Subjected to Dynamic Plastic Deformation at Cryogenic Temperature F. Yan, H.W. Zhang† , N.R. Tao and K. Lu Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China [Manuscript received April 12, 2011, in revised form May 30, 2011] A pure Cu (99.995 wt%) has been subjected to dynamic plastic deformation at cryogenic temperature to a strain of 2.1. Three types of microstructures that are related to dislocation slip, twinning and shear banding have been quantitatively characterized by transmission electron microscopy (TEM) assisted by convergent beam electron diffraction (CBED) analysis. Microstructures originated from dislocation slip inside or outside the shear bands are characterized by low angle boundaries (<15◦) that are spaced in the nanometer scale, whereas most deformation twins are deviated from the perfect Σ3 coincidence (60◦/<111>) up to the maximum angle of 9◦. The quantitative structural characteristics are compared with those in conventionally deformed Cu at low strain rates, and allowed a quantitative analysis of the flow stress-structural parameter relationship. KEY WORDS: Quantitative structural characterization; Cu; Dynamic plastic deformation; Trans￾mission electron microscopy; Convergent beam electron diffraction 1. Introduction There is a current interest in the microstructural refinement by plastic deformation at high strain rates and low temperature[1–4]. Generally, three types of deformation mechanisms are activated in metals with low stacking fault energy (SFE) such as Cu and Cu￾alloy, i.e. dislocation slip, twinning and shear banding (SB)[1,2]. The microstructural refinement induced by these three mechanisms is different, with the smallest value (47 nm) by twinning, followed by SB (75 nm) and dislocation slip (121 nm)[1]. However, detailed microstructural characters including the structural parameters such as boundary misorientation angles, fraction of high or low angle boundaries and the dis￾location density between and in the boundaries are lacking, whereas these parameters play a crucial role in understanding the deformation mechanism and the structure-strength relationship. It is thus the objec￾tive of the present study to quantify the structural † Corresponding author. Tel.: +86 24 23971890; E-mail ad￾dress: hwzhang@imr.ac.cn (H.W. Zhang). parameters and to set up the relationship between flow stress and these parameters. The material chosen for investigation was high￾purity Cu (99.995 wt%) processed by dynamic plas￾tic deformation (DPD) at cryogenic temperature to a strain of 2.1. TEM (transmission electron mi￾croscopy) based CBED (convergent beam electron diffraction) technique was used to quantify the mi￾crostructural parameters. The structural characteris￾tic as well as the strengthening mechanism has been discussed. 2. Experimental High-purity polycrystalline Cu (99.995 wt%) in the form of cylinder (9 mm in diameter and 12 mm in thickness) was subjected to DPD at cryogenic temper￾ature (liquid nitrogen), which is denoted as LN-DPD Cu. Prior to DPD, the sample was annealed at 973 K for 2 h in order to remove the residual stress and to obtain the fully-recrystallized structures. The start￾ing material is composed of equiaxed recrystallized grains with an average size of 200 μm and a fraction