On the Influence of Grain Boundary Misorientation on the Severe Plastic Deformation of Aluminum Bicrystals: A Three-Dime
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TRODUCTION
GRAIN boundaries (GBs) are one of the most important features for metallic materials since they act as obstacles to dislocation motion during plastic deformation.[1–5] The pileup of dislocations at the site of GBs significantly increases the yield strength of deformed metals.[6] Therefore, the formation of more GBs when producing ultrafine-grained metals entails an increase in yield strength with the decrease of the grain size, a phenomenon known as the Hall–Petch relation.[7,8] In general, low-angle grain boundaries (LAGBs) are not able to resist the plastic flows compared to high-angle
M. LIU, S. NAMBU, and T. KOSEKI are with the Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656, Japan. Contact e-mail: [email protected] K. ZHOU is with the School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. P.F. WANG is with the CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei 230027, China. G. LU is with the Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Vic 3122, Australia. C. LU and K.A. TIEU are with the School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, Wollongong, NSW 2522, Australia. Manuscript submitted September 24, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
grain boundaries (HAGBs) because the dislocations can easily penetrate them and glide into the neighboring crystal. The deformation mechanism of GBs has been extensively studied for polycrystalline metals.[1,9,10] However, there is a limitation by using polycrystalline materials to conduct the research of an individual GB because one single grain is connected by different grains and its mechanical properties may also be affected by other GBs. Therefore, bicrystalline metals are the best candidates for discovering the influence of an individual GB on the mechanical properties and misorientation evolutions of two adjacent grains. The deformation behaviors of bicrystals have also been systematically studied by different materials, such as aluminum,[11,12] copper,[13] and magnesium.[14] Despite the fact that numerous research studies of GBs have been done by using bicrystals, none of them were under severe plastic deformation (SPD) conditions, e.g., high-pressure torsion, surface mechanical attrition treatment, twist extrusion,[15] and accumulative roll bonding, owing to the complicated deformation process. There is a concern about how a GB will behave during SPD. Fortunately, equal-channel angular pressing (ECAP) as one of the SPD methods can be used to investigate the GB behavior since it is a comparatively simple process to conduct. To date, there is only limited research related to the bicrystals subjected to ECAP deformation. Han et al.[16] carried out one-pass ECAP experiments using Cu bicrystals to investigate the evolution of GBs with
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