Preparation and Mechanical Properties of Hafnium-based Bulk Metallic Glasses
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Preparation and Mechanical Properties of Hafnium-based Bulk Metallic Glasses Xiaofeng Gu, Li-qian Xing and T. C. Hufnagel Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218, U.S.A.
ABSTRACT We have prepared bulk metallic glasses of composition (HfxZr1-x)52.5Cu17.9Ni14.6Al10Ti5 (with x=0-1) by an arc melting/suction casting method. The density of these alloys increases by nearly 67% with increasing Hf content, which is advantageous for their potential use as kinetic energy armor-piercing projectile materials. The glass transition temperature and the melting temperature increase linearly with increasing Hf content. The reduced glass transition temperature (Tg/Tm) decreases from 0.64 (x=0) to 0.62 (x=1), indicating reduced glass-forming ability for the Hfbased alloy. The fracture strength in uniaxial compression at quasi-static strain rates also increases with increasing Hf content, reaching ~ 2.2 GPa for Hf52.5Cu17.9Ni14.6Al10Ti5. INTRODUCTION Multi-component Zr-based bulk metallic glasses have been produced by simple casting methods with cooling rates of 102 K/sec or less since 1990s [1-3]. The reduced glass transition temperature (Trg, defined as the ratio of glass transition temperature to the melting temperature) of these alloys approaches the theoretically predicted value of 2/3 [4]. As a result, these metallic glasses can be made in relatively large dimensions and have a wide supercooled liquid range, which makes it convenient to investigate both mechanical and thermal properties. Due to the absence of crystalline slip, the mechanical properties of metallic glasses are quite unlike those of conventional crystalline materials. A good example is that shear deformation is highly localized in metallic glasses. As a result, metallic glasses exhibit relatively low fracture toughness and very small macro-plasticity [5-10]. In kinetic energy armor-piercing projectiles, however, formation of shear bands allows the penetrator to slough off the deformed material. This prevents a “mushroom” head from building up on the penetrator during impact, allowing it to penetrate more effectively [11]. A potential limitation, however, is that the density of existing Zr-based metallic glasses (~ 6.6 g/cm3) is too low for this application. In this paper, we report successful preparation of a series of Hf-based glass-forming alloys with the composition (HfxZr1-x)52.5Cu17.9Ni14.6Al10Ti5 ( x=0, 1/3, 1/2, 2/3, 1). The density of these alloys increases significantly with increasing Hf content, reaching a maximum of 11.09 g/cm3 for Hf52.5Cu17.9Ni14.6Al10Ti5. Due to the chemical similarity of Zr and Hf, these alloys still retain good glass-forming ability. The reduced glass transition temperature decreases slightly. The fracture strength of these alloys also increases with increasing Hf content, reaching a maximum of ~ 2.2 GPa for Hf52.5Cu17.9Ni14.6Al10Ti5.
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EXPERIMENTAL DETAILS We arc-melted mixtures of pure elements (>99.95%) with the nominal composition of (HfxZr1-x)52.5Cu17.9Ni14.6Al1
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