Structural rejuvenation in a bulk metallic glass induced by severe plastic deformation W. Dmowski a, * , Y. Yokoyama b , A. Chuang a , Y. Ren c , M. Umemoto d , K. Tsuchiya e , A. Inoue b , T. Egami a,f,g a Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996-2200, USA b Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan c Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA d Department of Production Systems Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan e National Institute for Materials Science, Tsukuba 305-0047, Japan f Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996-1200, USA g Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6376, USA Received 11 June 2009; received in revised form 1 September 2009; accepted 9 September 2009 Available online 6 October 2009 Abstract Using high-energy X-ray diffraction we examined the atomic structure in bulk metallic glass samples which underwent severe plastic deformation by the high-pressure torsion (HPT) technique. We obtained the atomic pair distribution function (PDF) and determined the changes in the PDFs due to deformation. The observed changes in the PDF clearly show structural disordering, which suggests structural rejuvenation by heavy deformation. However, the changes cannot be explained simply in terms of creating excess free volume, and they indicate that much more extensive atomic rearrangements take place as a consequence of deformation. Also, we suggest that the observed structural change may well be an outcome of local heating due to deformation and may not directly provide the knowledge of the atom- istic mechanism of strain localization. Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: X-ray diffraction; Bulk amorphous materials; Plastic deformation; Pair distribution function 1. Introduction Metallic glasses (MGs) are structurally disordered solids which are typically obtained by rapid quenching from the melt. MGs have been studied vigorously since the first report on amorphous gold–silicon alloy back in 1960 [1]. The devel- opment of bulk metallic glasses (BMGs) [2–5] made it possi- ble for glassy samples to reach a centimeter in size. The large samples allow the study of mechanical properties for engi- neering applications. The random atomic arrangement in metallic glass contributes to many outstanding properties such as high strength [6], high elastic limits [7,8], and good corrosion resistance [9,10], among others. However, limited macroscopic plastic deformability at room temperature is a major drawback, which severely restricts structural applica- tions of BMGs. The amorphous metallic alloys deform in a highly localized mode, where a large amount of plastic strain is accumulated in very thin 10 nm narrow regions known as shear bands, and exhibit a strain-softening behavior (e.g. [11,12]). Once the sample starts to yield in most cases it is soon followed by a catastrophic failure. Although the plastic strain is high in the localized area, the macroscopic plasticity is extremely low (e.g. [12]). This inhomogeneous mode of deformation occurs at large applied stresses and low temperatures [13]. Understanding the initiation and operation of shear bands is critical for both fundamental research and practical application. Since the deformation appears to be localized in the shear bands, most of the structural studies were done so 1359-6454/$36.00 Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.actamat.2009.09.021 * Corresponding author. Tel.: +1 865 974 2268; fax: +1 865 974 4115. E-mail address: wdmowski@utk.edu (W. Dmowski). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 58 (2010) 429–438