Plastic deformation studies of Zr-based bulk metallic glassy samples with a low aspect ratio D.V. Louzguine-Luzgin a,n , S.V. Ketov a , Z. Wang a , M.J. Miyama a , A.A. Tsarkov b , A.Yu. Churyumov b a WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan b National University of Science and Technology “MISiS”, Moscow, 119049, Russia article info Article history: Received 30 June 2014 Received in revised form 29 July 2014 Accepted 1 August 2014 Available online 11 August 2014 Keywords: Bulk metallic glasses Mechanical properties Relaxation enthalpy Strain abstract In the present work Zr-based bulk metallic glassy samples with low aspect ratio (1:2) were deformed plastically at quasistatic loading conditions in order to study propagation of relatively homogeneous plastic deformation without clear shear localization in a dominant shear band that was observed in the samples with larger aspect ratio. Usage of low aspect ratio allows achieving large plastic deformations without fracture by forming multiple shear bands. The experimental results are discussed and compared with those of molecular dynamics and finite elements model computer simulation. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Bulk metallic glasses (glassy alloys) have been obtained in different alloy systems up to several centimeters in thickness [1,2] by using mold casting or water cooling processes. Zr–Cu- and Pd–Ni- based alloys are the best metallic bulk glass-formers known to date [3]. The glass-forming ability of the quaternary and ternary bulk metallic glasses is significantly higher than that of binary alloys in accordance with the principles for achieving high glass-forming ability [1,4]. Bulk metallic glasses exhibit high hardness, wear resistance and mechanical strength [5,6] but in general suffer from low plasticity at room temperature [7,8]. Strongly localized shear deformation at room temperature limits the practical application of BMGs [9,10] since any shear event may trigger a critical size crack initiation [11,12] and rapid fracture of the sample. On the other hand, the samples of recently developed BMGs, such as Pd–Ni–Si–P [13], Ti–Zr–Cu–Ni–Sn [14] and Zr–Cu– Fe–Al [15] system alloys, exhibit significant room temperature compressive plasticity of several percents and high fracture strength in the glassy state. At the same time, the exact mechan- ism of shear band propagation is still a debatable question [16,17]. Except for the thin film type sample which deforms rather homogeneously [18,19] deformation of metallic glasses takes place by the formation of highly localized shear bands [20,21] in the beginning of plastic deformation process and stick–slip serrated flow behavior localized in a dominant shear band is also observed at the later stage [22,23]. Nanocrystallization was found in the heavily deformed areas under compression [24,25]. Propagation of the shear bands was also studied by a high-speed camera [26] and acoustic emission [27]. Recently, it was found that minor shear bands can be initiated even at stresses which are well below the proof stress [28]. It was also shown that room temperature uniaxial compression of a Zr-based bulk metallic glass at 80% of the yield stress leads to minor homogeneous deformation of the sample [29]. It was found that the mechanical strength variation of BMGs is scaled with the occurrence frequency and volume fraction of cast defects [30]. Also, porous metallic glasses [31,32] and crystal glassy composites exhibit higher plasticity than their metallic glassy counterparts [33,34]. Phase transformations were observed, recently, upon cyclic loading of the Zr 62.5 Fe 5 Cu 22.5 Al 10 bulk metallic glassy samples. It is found that kinetically frozen anelastic deformation accumulates at room temperature and causes crystallization of metallic glassy phase forming either precursors of a metastable crystalline phase [35] or clear crystalline nanoparticles [36] depending on the sample size and the applied load. Such a nanocrystallization may be treated as a consequence of anelastic effects connected with operation of the localized areas of viscoelastic deformation [37], taking place even in the deformation regime that is characterized by the linear character of the stress–strain curve. Cyclic hardening Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/msea Materials Science & Engineering A http://dx.doi.org/10.1016/j.msea.2014.08.006 0921-5093/& 2014 Elsevier B.V. All rights reserved. n Corresponding. author. Tel.: þ81 22 217 5957; fax: þ81 22 217 5956. E-mail address: dml@wpi-aimr.tohoku.ac.jp (D.V. Louzguine-Luzgin). Materials Science & Engineering A 616 (2014) 288–296