13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Failure mode transition of Zr-based bulk metallic glass Fan Zeng1, LanHong Dai1,* 1State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, PR China * Corresponding author: lhdai@lnm.imech.ac.cn Abstract Zr41.2Ti13.8Cu10Ni12.5Be22.5 (Vit 1) bulk metallic glass (BMGs) exhibits different failure modes under low strain rate (10-4s-1) and high strain rate (103s-1) uniaxial compression at room temperature. Quasistatically deformed samples often fail along one dominant shear band and fracture into two large millimeter-scale blocks, whereas at impulsive loading, the samples usually break into many small scale fragments with rough fracture surfaces, such as non-uniformly distributed vein patterns and micro multiple shear bands (network-like shear bands). A theoretical model that takes into account the balance between the energy dissipation within shear band and the stored energy released in the vicinity of the shear band to fuel shear localization is developed. Furthermore, the underlying mechanisms of one dominant shear band and network-like multiple shear bands controlling the failure mode transition are revealed. Keywords: Compression test; Bulk metallic glass; Failure mode; Shear bands. 1. Introduction Because of their unique properties such as high room-temperature(RT) strength and large elastic limit, bulk metallic glasses (BMGs) as a potential engineering and structural material have triggered extensive scientific interest over the years [1-5].However, the poor macroscopic plastic deformation ability of BMGs limits their application. Therefore, the need for a more fundamental understanding of the deformation and failure mechanisms in BMGs has motivated numerous experimental investigations, especially under high strain rate. It has been found that some tough amorphous metals, such as Zr- and Pd-based metallic glasses, often fail along a narrow shear band both under quasi-static and dynamics compressive loading[6-10]. But some authors reported that the dynamically BMG samples fractured into several fragment similar to the failure behavior of some brittle Mg-,Fe-,and Co-based metallic glasses subjected to quasi-static loading[11, 12]. In this paper, we find that the failure mode of Zr41.2Ti13.8Cu10Ni12.5Be22.5 (Vit1) bulk metallic glass (BMGs) was dependent of the strain rate in compression at room temperature. And, we develop local evolution model of the shear band, as to why Zr-based metallic glass exhibit the different failure modes. 2. Experimental The Zr41.2Ti13.8Cu10Ni12.5Be22.5 bulk metallic glass was prepared by arc melting high purity composition elements together in a Ti-gettered purified argon atmosphere. Each ingot was re-melted several times to ensure homogeneity and then prepared by suction-casting the molten alloy into a copper mold to form rods (Φ5×100mm). Quasi-static and dynamic compression tests were performed on a MTS-810 material testing machine and SHPB using cylinders 5 mm in diameter and 7.5 mm height. In quasi-static compressive test, the strain rate was fixed at 1.0×10-4s-1. In dynamic compression, the strain rate ranged from 1.0×103s-1 to 2.5×103s-1. After testing, the scanning electron microscopy (SEM) was used to characterize the fracture morphology of all specimens. 3. Results
RkJQdWJsaXNoZXIy MjM0NDE=