Materials Science and Engineering A 487 (2008) 144–151 Ductile to brittle transition of Cu 46 Zr 47 Al 7 metallic glass composites J.T. Fan a , Z.F. Zhang a,∗ , F. Jiang b , J. Sun b , S.X. Mao a,c a Shenyang National Laboratory for Materials Science, Institute of Metal Research, The Chinese Academy of Science, Shenyang 110016, People’s Republic of China b State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China c Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA Received 1 August 2007; received in revised form 30 September 2007; accepted 16 October 2007 Abstract The ductile to brittle transition behaviors of Cu 46 Zr 47 Al 7 metallic glass and its composite with different microstructures were systematically evaluated by Vickers hardness and small punch test, on the base of the uniaxial compression properties reported before. It was found that the metallic glass composite containing different volume fraction of primary crystallization phases displayed a transition from ductility to brittleness, which can be well revealed by both the Vickers hardness and the small punch tests. For example, the number of shear bands appearing around the indentation of Vickers hardness trends to decrease with the increase in the volume fraction of primary crystallization phases in the metallic glass composites. After small punch tests, the shear deformation and failure behaviors were also found to display obvious ductile to brittle transition. And even the small punch test can distinguish the difference in their intrinsic shear deformation ability more delicately. Based on the experimental results above, the ductile to brittle transition in the metallic glass composite was discussed. © 2007 Elsevier B.V. All rights reserved. Keywords: Metallic glass; Shear bands; Ductility; Brittleness; Small punch test 1. Introduction Bulk metallic glasses (BMGs) have been found in many alloy systems, which has attracted tremendous attention since their first emergence about 40 years ago [1–5]. At the same time, they also offer unique potential as structural materials for high strength, high hardness, good wear and corrosion resistance [6,7]. Unfortunately, these properties cannot be fully exploited in monolithic amorphous metals due to the lack of plasticity in unconfined loading geometries. In order to improve the plastic- ity, many investigations have been carried out by introducing a reinforcing phase into the BMG matrix, which introduces a new kind of material, the BMG matrix composite [8,9]. Recently, it is interesting to find that the Zr–Cu–Al ternary alloys have a better combination of high strength, good ductility and lower production cost, compared with the other BMG alloys [10–12]. It was reported that Cu 47.5 Zr 47.5 Al 5 BMG exhibited sound “work hardening” and large plastic strain of 18% together with a high-compressive strength of up to 2265 MPa [13]. Besides, ∗ Corresponding author. E-mail address: zhfzhang@imr.ac.cn (Z.F. Zhang). plasticity-improved Zr–Cu–Al BMG matrix composites were also fabricated with many martensite phases [14]. However, the small size, seldom larger than 4 mm in diameter, limits its appli- cation as structural materials. To reveal the deformation and fracture mechanism of metallic glasses and their composites, the conventional experimental tests, for example uniaxial compres- sion, tension, bending and so on, were always employed [5,15]. It is widely observed that metallic glasses often exhibit brittle frac- ture under tension, and different plasticity under compression [5,12–17]. This gives rise to an interesting question: whether one can find some novel testing method to further reveal the dif- ference in the deformation and fracture mechanisms of different metallic glasses and their composites? In this paper, a Cu 46 Zr 47 Al 7 alloy was cast into wedge shape with thickness up to 9 mm. The different thickness of the bulk samples led to varying cooling rates upon solidification, and furthermore resulted in different microstructures and volume fraction of primary crystallization phases. Therefore, it is con- venient to compare the transition in the mechanical properties and the corresponding deformation and fracture mechanism. For better understanding such transition, besides the conven- tional Vickers hardness tests, we employed a new test method, i.e., small punch test, to further reveal the difference in the 0921-5093/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.10.036