Papers by Keyword: Bulk Metallic Glass (BMG)

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Authors: Hui Qiang Li, Long Fei Liu
Abstract: With the effects of electronic structure and atomic size being introduced, a revised model to calculate the viscosity of the bulk metallic glass alloys was proposed and the viscosity of ternary Zr-Al-Cu, Zr-Ni-Al and quaternary Zr-Al-Ni-Cu systems are calculated in this paper, and the computed results agree well with the empirical one. The sequence of viscosity of different systems is: VZr-Al-Cu <VZr-Al-Ni<.VZr-Al-Ni-Cu. To Zr-Al-Cu and Zr-Ni-Al, the highest viscosity locates in the composition range of XZr=0.37-0.86, XCu=0-0.40 and XZr = 0.45-0.79, XAl = 0.12-0.50, respectively. And to the Zr-Ni-Al-Cu system with 66.67% Zr, the highest viscosity is obtained in the region of XAl= 0.63-0.80, XNi = 0.14-0.24.
Authors: Tiburce A. M. Aboki
Abstract: We have subjected Zr59Cu20Al10Ni8Ti3 glassy sample to internal friction thermal cycle (IFTC) measurements under various conditions involving changes in heating/cooling rate, strain amplitude and frequency. Additional low temperature internal friction peaks (ALTIFP) were found to occur with the characteristic low temperature internal friction peak (CLTIFP) observed for some glassy alloys. The ALTIFP were enhanced on heating and reduced on cooling. Their strength increase following the number of IFTC can be related to a stress concentration in some zones of the glassy structure, which is abruptly relaxed by the viscous flow creating interfaces in the glassy structure. These interfaces are likely to be formed between atomic clusters. The growth of the ALTIFP increases significantly the whole IF level (IFL) from 10-4 to 10-2 enhancing the damping capacity of the glassy sample.
Authors: Alain Reza Yavari, S. Pang, Dmitri V. Louzguine-Luzgin, Akihisa Inoue, N. Lupu, N. Nikolov, G. Heunen
Authors: Akihiko Hirata, Yoshihiko Hirotsu, Kenji Amiya, Nobuyuki Nishiyama, Akihisa Inoue
Abstract: Nanoscale structural change in (Fe0.5Co0.5)72B20Si4Nb4 bulk glassy alloy on annealing has been investigated using transmission electron microscopy. On annealing at temperatures above 773K, electron diffraction intensity analysis showed a clear structure change for a Cr23C6-type local atomic ordering. The local structure formation of Cr23C6-type nanophase was confirmed by nanobeam electron diffraction. A development process of dense precipitates of the Cr23C6-type nanophase was further studied by high-resolution electron microscopy. It was found that the formation of the highly-dense nanoprecipitates provides an increase in Vickers hardness.
Authors: Jian Sheng Gu, Hui Feng Bo, Hong Li, Zhan Xin Zhang
Abstract: Shear banding characterization of Zr64.13Cu15.75Ni10.12Al10 and Zr65Cu15Ni10Al10 BMGs was studied by using Rockwell indention method. Well-developed shear band pattern can be found for both BMGs after indentation. The significant difference in plastic deformation ability can be ascribed to different shear banding features.
Authors: Qing Wang, Chun Lei Zhu, Yan Hui Li, Jiang Wu, Chuang Dong, Jian Bing Qiang, Wei Zhang, Akihisa Inoue
Abstract: The present paper investigates the bulk metallic glass formation in Co-based alloy systems with the guidance of the cluster line and minor-alloying principles. The selected basic ternary Co-B-Si alloy compositions are intersecting points of cluster lines, defined by linking special binary clusters to the third element. Then these basic ternary alloys are further minor-alloyed with Nb and quaternary bulk metallic glasses are obtained only by 4-5 at. % Nb minor-alloying of the basic composition Co68.6B25.7Si5.7 that is developed from dense-packed cluster Co8B3. The bulk metallic glasses are expressed approximately with a unified simple composition formula: (Co8B3)1(Si,Nb)1. In addition, a quantity of Fe substitution for Co further improves the glass-forming abilities.
Authors: Ya Juan Sun, Ri Ga Wu, Hong Jing Wang
Abstract: The mechanical properties of a new Zr-based bulk metallic glass at low temperatures were investigated. The results indicate that the fracture strength increases significantly (4.9%) and the global plasticity increases somewhat when testing temperature is lowered to 123K. The stress-strain curve of the sample deformed exhibits more serrations and smaller stress drop due to formation of more shear bands at low temperature than at room temperature.
Authors: J.K. Lee, H.J. Kim, Taek Soo Kim, Seung Y. Shin, Jung Chan Bae
Abstract: Bulk metallic glass (BMG) composites combining a Cu54Ni6Zr22Ti18 matrix with brass powders or Zr62Al8Ni13Cu17 metallic glass powders were fabricated by spark plasma sintering. The brass powders and Zr-based metallic glass powders added for the enhancement of plasticity are well distributed homogeneously in the Cu-based metallic glass matrix after consolidation. The matrix of the BMG composite remains as a fully amorphous structure after spark plasma sintering. The BMG composites show macroscopic plasticity after yielding, and the plastic strain increased to around 2% without a decrease in strength for the composite material containing 20 vol% Zr-based amorphous powders. The proper combination of strength and plasticity in the BMG composites was obtained by introducing a second phase in the metallic glass matrix.
Authors: S.K. Sharma
Abstract: Amorphous alloys, in general, exhibit superior mechanical and chemical properties as compared to their crystalline counterparts, which is attributed to their chemical homogeneity and to the absence of crystal-like structural defects. Nanocrystalline and fully crystallized forms of these alloys can be easily obtained by a suitable thermal annealing treatment. It is important to have the knowledge of corrosion/oxidation behavior of amorphous and nanocrystalline alloys for various possible applications. In contrast to many investigations on corrosion and oxidation behavior of amorphous alloys reported in the literature, only limited studies have been carried out on comparison of corrosion/oxidation behavior of amorphous and nanocrystalline states of the same alloy. With this motivation potentiodynamic polarization studies were carried out on amorphous and nanocrystalline states of the alloy Ti60Ni40 in several aqueous media at room temperature. The oxidation in air was also investigated in the temperature range 2800C-3800C using a thermogravimetric analyzer. It was found from these investigations that nanocrystalline state exhibits the maximum corrosion/oxidation resistance in comparison to amorphous and crystalline states. The better corrosion/oxidation resistance of nanocrystalline state can be explained in terms of the nature of the nanocrystalline phase/phases and the size of the crystallites. The results of the present study are supported by other similar studies reported in the literature. A short review on comparison of corrosion/oxidation behaviour of amorphous and nanocrystalline Ti-based alloy is also presented in the paper.
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