Effect of Strain Rate on Evolution of the Deformation Microstructure and Texture in Polycrystalline Copper and Nickel
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INTRODUCTION
DEFORMATION texture evolution in a variety of materials has been studied extensively under different deformation modes such as tension, compression, rolling, and torsion. Most of these studies have been carried out for processing at normal strain rates and temperature.[1] Only a few reports are available that investigate texture evolution under nonambient conditions like very high strain rates (dynamic loading condition) and pressure.[2,3] It is expected that the material response to imposed stress and strain boundary conditions may differ significantly from one under normal conditions. This could be a result of the presence of additional accommodation mechanisms like twinning and even phase transformation in certain cases under these conditions.[4] It is, therefore, expected that texture evolution under nonambient conditions would be substantially different than under normal testing conditions. Of particular interest is the material behavior under dynamic loading conditions, as various crystal-plasticity-based deformation texture evolution models consider slip to be rate insensitive.[5,6] In the present investigation, a study has been carried out to examine the rate effects on texture evolution for NILESH P. GURAO, Ph.D. Student, and SATYAM SUWAS, Assistant Professor, are with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India. Contact e-mail: [email protected] RAJEEV KAPOOR, Scientist at Materials Division, is with Bhabha Atomic Research Centre, Mumbai 400085, India. Manuscript submitted August 12, 2009. Article published online July 22, 2010 2794—VOLUME 41A, NOVEMBER 2010
oxygen-free high thermal conductivity (OFHC) copper and nickel over seven orders of magnitude of strain rate ranging from 3 9 104 to ~2.0 9 10+3 s1. The facecentered cubic (fcc) metals are characterized by medium and high stacking fault energy (SFE) with the values cCu = 78 mJ/m2 and cNi = 130 mJ/m2, respectively. However, they possess similar normalized SFE (c/Gb, where G is the shear modulus and b is the Burger vector) and, therefore, are best suited for high strain rate studies, as additional deformation mechanisms like twinning are not expected to play a dominant role under dynamic loading conditions. This helps in studying the rate effect on texture evolution only caused by slip. Experimental investigations pertaining to texture evolution as a function of strain rate have been sparse. The most profound investigation carried out to date is by Leffers,[7] who reported that rolling texture evolution in Cu-5 pct Zn is rate dependent. Leffers and Pederson[8] showed that a combination of strain rate and temperature can be used to get a particular type of texture in rolling of Cu-5 pct Zn. It was proposed that the activation energy for cross slip that governs the evolution of texture is not only temperature dependent but also strain rate dependent, which was attributed to the dependence of texture evolution on strain rate. Kocks and Mecking[9] showed that the increase in strain rate leads
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