Dynamic recrystallization in high-purity aluminum single crystal under frictionless deformation mode at room temperature
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Heung Nam Han Department of Materials Science and Engineering and center for Iron and Steel Research, RIAM, Seoul National University, Seoul 151-744, Korea
Suk Hoon Kang and Jinsung Jang Nuclear Material Research Division, Korea Atomic Energy Research Institute, Yuseong-gu, Daejeon 305-353, Korea
Jun Hyun Hana) Department of Nanomaterials Engineering, Chungnam National University, Daejeon 305-764, Korea (Received 6 April 2013; accepted 30 August 2013)
Dynamic recrystallization (DRX) of 99.9999% aluminum single crystal at room temperature was examined under frictionless deformation mode. To exclude the self-heating of the specimen due to applied high strain, a microcrack that localizes the stress at a very small region was intentionally introduced by controlled local necking. For the in situ observation of DRX, a specially designed in situ microdeformation device was positioned inside an electron backscattered diffraction system chamber. Recrystallized grains showed relatively random texture and preferred growth direction. The subgrains with low-angle grain boundaries formed by dynamic recovery transformed into small grains with high-angle grain boundaries, acting as nuclei for discontinuous dynamic recrystallization and growing by further deformation. The DRX in pure aluminum can take place under frictionless tensile deformation conditions at room temperature, and the stress localization and high purity are key issues for the DRX of aluminum at room temperature.
I. INTRODUCTION
When a metallic material is deformed plastically at high temperature, the storage and elimination of dislocations can occur simultaneously, which is known as “dynamic recrystallization” (DRX).1–4 For DRX, a large number of dislocations is accumulated and eliminated by the migration of high-angle grain boundaries (HAGBs). In general, there are two types of DRX: (i) continuous dynamic recrystallization (CDRX), which involves the transformation of low-angle grain boundaries (LAGBs) into HAGBs due to increases in misorientation (h) by the progressive accumulation of dislocations at subgrain boundaries, and (ii) discontinuous dynamic recrystallization (DDRX), which occurs by the nucleation and growth mechanisms of grains with HAGBs.5–13 However, the high stacking fault energy of aluminum results in the cross-slip and climb of dislocations, such that the value of the stored energy is too low to cause DRX. Therefore, the energy restoration of aluminum generally takes place not through DRX but through dynamic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.265 J. Mater. Res., Vol. 28, No. 20, Oct 28, 2013
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recovery (DRV).14 Nevertheless, several researchers have reported that DRX could take place in aluminum in special conditions, such as equal channel angular extrusion, cyclic deformation, and hot compression at high temperature.5,15–20 Most previous reports indicated that appropriate temperature was necessary for the occurrence of DRX. Yamagat
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