Effects of Zr and Si on the Glass Forming Ability and Compressive Properties of Ti-Cu-Co-Sn Alloys
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BULK metallic glasses (BMGs) have drawn great research interest in material science and engineering owing to their extraordinary properties arising from their disordered atomic structure.[1 5] Since the first discovery of Au-Si metallic glass in 1960,[6] a variety of BMGs have been developed in Mg-, La-, Zr-, Pd-, Ti-, Fe-, Co-, Ni-, and Cu-based systems.[1] Of the developed glassy alloys, Ti-based BMGs are especially attractive due to their low density, high specific strength, low elastic modulus, good corrosion resistance, and excellent biocompatibility.[7 12] Up to now, a number of Ti-based BMGs, such as Ti-Cu-Ni-Sn,[13] Ti-Cu-Ni-Si-B,[14] TiCu-Ni-Sn-Be,[15] Ti-Zr-Cu-Ni-Be,[7] Ti-Cu-Ni-Al-Zr-SiB,[16] Ti-Zr-Hf-Cu-Ni-Si,[17] Ti-Zr-Cu-Ni,[18] Ti-Zr-CuNi-Sn,[19] Ti-Zr-Hf-Cu-Ni-Si-Sn,[20] Ti-Zr-Cu-Pd-Sn,[21] Ti-Zr-Be, Ti-Zr-Be-Cr,[22] Ti-Zr-Be-V,[23] and Ti-Zr-BeAl-Cu,[8] have been developed by the composition design. It is found that all of these Ti-based BMGs exhibit two compositional features. (1) Some Ti-based BMGs consist of biological toxic elements, Be and Ni, to improve their glass forming ability (GFA). The release of nickel ions may not only cause biological effects, but also is the origin of the most widespread contact allergy.[24] (2) Noble metals such as Pd and Ag have been added, which confines the extensive industrial application of Ti-based BMGs. Therefore, it is of
TAN WANG, YIDONG WU, and JIAJIA SI, Ph.D. Candidates, and XIDONG HUI, Professor, are with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: xdhui@ustb. edu.cn Manuscript submitted April 29, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
significance to explore a new kind of Ti-based BMGs free of noble metals and toxic elements. It is also seen that most Ti-based BMGs contain Zr elements. The addition of Zr has been proven to play an important role in the glass formation, thermal stability, and properties of BMGs.[25] Kim et al.[7] increased the critical diameter of glass formation from 2 to 5 mm through replacement of Ti by Zr in the Ti-Cu-Ni-Sn-Be alloy system. The addition of Si in Ti-based BMGs has a remarkable effect on the GFA and mechanical properties. The minor addition of Si increased the critical diameter from 2.2 to 5 mm[17] in Ti-Zr-Hf-Cu-Ni alloys. The enhancement in GFA was considered to originate from the intrinsic role of the alloying elements in destabilizing the competing crystalline phase and stabilizing the undercooled liquid phase.[26] In contrast, the research by Zhu et al.[27] indicated that the addition of Si caused the decrease of GFA and the increase of supercooled liquid region as the concentration of Si was higher than 2 pct in Ti-based alloys. They pointed out that the fragility of Ti-based alloy increased, although the addition of Si improved the thermal stability. Angell introduced the concept of fragility,[28] which is an effective way to evaluate relaxation dynamics and the GFA of the supercooled liquids.
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