桃李不言

各位同行：

鉴于iblog近期经常出现各种各样的问题，博主决定迁址至http://amorphous.ycool.com/，本博客即日起停止更新，感谢你们一直以来的关注！

Relationship between structure, dynamics, and mechanical properties in metallic glass-forming alloys

Y. Q. Cheng,¹ H. W. Sheng,² and E. Ma¹

¹Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA

²Department of Computational and Data Sciences, George Mason University, Fairfax, Virginia 22030, USA

(Received 23 June 2008; published 30 July 2008)

Using Cu-Zr models, we demonstrate icosahedral ordering as a microscopic origin of the non-Arrhenius dynamical slowing down in metallic supercooled liquids. This correlation between the structural and dynamical heterogeneities underlies the evolution of the energy barrier for relaxation upon undercooling, as well as the eventual glass transition that leads to the formation of bulk metallic glasses (MGs). Our analysis of the energy barrier to plastic relaxation in MGs relates their macroscopic strength and plasticity to the local structures developed in the MGs. The structure-dynamics perspective explains not only the composition-dependent mechanical properties but also the known correlation between the strength of MGs and the glass transition temperature.

1.New processing possibilities for highly toughened metallic glass matrix composites with tensile ductility
Pages 684-687
Douglas C. Hofmann, Jin-Yoo Suh, Aaron Wiest and William Johnson

2.Dynamic compression of a zirconium-based bulk metallic glass confined by a stainless steel sleeve
Pages 688-691
M. Martin, L. Kecskes and N.N. Thadhani

3.Homogeneous deformation of bulk amorphous alloys during elastostatic compression and its packing density dependence
Pages 710-713
Kyoung-Won Park, Chang-Myeon Lee, Masato Wakeda, Yoji Shibutani, Eric Fleury and Jae-Chul Lee

Perspectives

MATERIALS SCIENCE:

Bulk Metallic Glasses

Cormac J. Byrne and Morten Eldrup^*

How BMGs measure up. (Bottom) A comparison of the strength and fracture toughness of a few selected BMGs with those of some crystalline metals and plastics. BMG properties are becoming increasingly competitive compared with those of other engineering materials. (Top) A sine diffraction grating prepared by pressing a Ni die into a MgCuY bulk metallic glass above its glass transition temperature (~165°C). The nanometer-scale replication is small enough to allow light to be diffracted.
CREDIT: COURTESY OF N. H. PRYDS (18)

1.A Dy-based bulk metallic glass with high thermal stability and excellent magnetocaloric properties
Pages 30-33
L. Liang, X. Hui, C.M. Zhang and G.L. Chen

2.Influence of low-temperature annealing on magnetic properties of (Nd_0.625Ni_0.375)₈₅Al₁₅ metallic glass
Pages 226-229
Feng Xu, Zhiming Wang, Guang Chen, Jianzhong Jiang and Youwei Du

3.Formation of centimeter Fe-based bulk metallic glasses in low vacuum environment
Pages 246-249
Jie Pan, Qi Chen, Ning Li and Lin Liu

4.Thermal stability and primary phase of Al–Ni(Cu)–La amorphous alloys
Pages 328-332
Zhenghua Huang, Jinfu Li, Qunli Rao and Youhe Zhou

Commentary

Nature Materials 7, 603 - 605 (2008)
doi:10.1038/nmat2234

Materials research in China

Lian Zhou¹, Hengde Li² & Changxu Shi³

Microstructure and magnetic property of Fe₅₃Nd₃₇Al₁₀ alloy

Q. Bai^a, H. Xu^a, X.H. Tan^a, H. Man^a, S.J. Wu^a and P.P. Cai^a

^aInstitute of Materials, Shanghai University, Shanghai 200072, PR China

Received 28 April 2008; revised 1 June 2008; accepted 4 June 2008. Available online 26 July 2008.

Abstract

The effect of cooling rate on microstructure and magnetic properties of Fe₅₃Nd₃₇Al₁₀ alloy prepared by different methods, i.e. suction casting and melt spinning, have been investigated. The Fe₅₃Nd₃₇Al₁₀ melt-spun ribbon exhibits a high coercivity, while the bulk alloy prepared by suction casting shows soft magnetic property. The hard magnetic property of the amorphous phase in the ribbon is attributed to the existence of the magnetically anisotropic face-centered cubic structure (a = 0.549 nm), which is correspondent with the metastable A_x phase in the as-cast Nd₆₀Fe₃₀Al₁₀ alloy. The amorphous phase with fully disordered microstructure is the reason for the soft magnetic property of the as-cast Fe₅₃Nd₃₇Al₁₀ alloy.

Keywords: Amorphous materials; Quenching; Anisotropy

Mechanical alloying of Fe_100−x−yNb_xB_y (x = 5, 10; y = 10, 15): From pure powder mixture to amorphous phase

J.J. Ipus^a, J.S. Blázquez^a, V. Franco^a and A. Conde^a

^aDepartamento de Física de la Materia Condensada, ICMSE-CSIC, Universidad de Sevilla, P.O. Box 1065, 41080 Sevilla, Spain

Received 25 April 2008; revised 10 June 2008; accepted 13 June 2008. Available online 26 July 2008.

Abstract

The mechanical alloying process of Fe₇₅Nb₁₀B₁₅ and Fe₈₅Nb₅B₁₀ systems has been studied from an initial mixture of elemental powders. The amorphization process is monitored by X-ray diffraction and Mössbauer spectrometry. An amorphous phase is formed after 400 h milling only for Fe₇₅Nb₁₀B₁₅ alloy, whereas a bcc supersatured solid solution is the final product after milling Fe₈₅Nb₅B₁₀ alloy. For both cases, a dispersion of  10% in the Fe content of the powder particles persists after 400 h milling. Powder particle size, Cr content and lattice parameter of bcc phase are larger for the alloy with the highest Nb content.

Keywords: A. Nanostructured intermetallics; A. Magnetic intermetallics; C. Mechanical alloying and milling

Preparation of a Zr-based bulk glassy alloy foam

Takeshi Wada^a, Xinmin Wang^a, Hisamichi Kimura^a and Akihisa Inoue^a

^aInstitute for Materials Research, Tohoku University, Katahira 2-1-1, Aobaku, Sendai, Miyagi 980-8577, Japan

Received 29 May 2008; revised 23 June 2008; accepted 13 July 2008. Available online 22 July 2008.

A Zr₄₈Cu₃₆Al₈Ag₈ bulk metallic glass (BMG) containing spherical pores with 3.9% porosity was prepared by melting a Zr₄₈Cu₃₆Al₈Ag₈ powder under 1.0 MPa pressurized helium. Annealing treatment of the porous alloy in a supercooled liquid region causes expansion of the pores. Highly porous BMG with a cellular structure was prepared by sudden reduction of the helium pressure in the crucible before quenching. The porous alloys exhibited significant plasticity due to a high density of shear bands initiated from pores.

Keywords: Metallic glass; Porous material; Foaming; Shear bands

Correlation between plasticity and fragility in Mg-based bulk metallic glasses with modulated heterogeneity

E. S. Park,¹ J. Y. Lee,¹ D. H. Kim,¹ A. Gebert,² and L. Schultz²

¹Center for Non-crystalline Materials, Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, South Korea
²Leibniz-Institute for Solid State and Materials Research IFW Dresden, P.O. Box 270016, nb vc01171 Dresden, Germany

A correlation between the kinetic fragility index (m) and enhanced plasticity is presented in Mg-based bulk metallic glasses (BMGs) with modulated heterogeneity by both suitable minor addition and optimal cooling rate. As case study, with minor addition of Gd in Mg₆₅Cu_7.5Ni_7.5Zn₅Ag₅Y_10−xGd_x BMG, plasticity as well as glass-forming ability improves in a wide composition range (2.5x7.5  at. %). Furthermore, the cooling rate can affect the structural heterogeneity and the deformability of BMGs. With increasing diameters for the alloy x=5, the compressive fracture strain increases from 2.97% at d=1  mm up to 3.74% at d=2  mm and then largely decreases. In particular, the variation of heterogeneity, which can directly affect in the property of BMG, can be evaluated by comparing the m values reflecting the inherent structure of BMGs. This concept can be used as a means of guiding alloy design and processing to alleviate brittleness of BMGs. ©2008 American Institute of Physics

Diffusion and structural relaxation in compositionally modulated amorphous metal films

M. P. Rosenblum, F. Spaepen, and D. Turnbull

Division of Applied Sciences, Harvard Unviersity, Cambridge, Massachusetts 02138

The interdiffusivity in compositionally modulated (25 Å) amorphous (Pd₈₅Si₁₅)₆₁/(Fe₈₅B₁₅)₈₉ and (Pd₈₀Au₇Si₁₃)₇₀/Fe₃₀ films has been measured by monitoring the satellite of the (000) x-ray scattering peak during isothermal anneals in the range 210–250 °C. Diffusivities as low as 10⁻²² cm² s⁻¹ have been measured. It was observed that the diffusivity decreased continuously during the annealing as a result of structural relaxation and settled down to a constant value only after many hours of annealing. The activation energy of the isoconfigurational diffusivity in the Pd-Au-Si/Fe films is 167 kJ mol⁻¹. This value and the time scale of the relaxation are similar to those observed in earlier viscosity measurements, indicating a similarity between the structural defects controlling both transport processes. Applied Physics Letters is copyrighted by The American Institute of Physics.

Shear band melting and serrated flow in metallic glasses

K. Georgarakis,¹ M. Aljerf,¹ Y. Li,¹ A. LeMoulec,¹ F. Charlot,¹ A. R. Yavari,¹ K. Chornokhvostenko,² E. Tabachnikova,² G. A. Evangelakis,³ D. B. Miracle,⁴ A. L. Greer,⁵ and T. Zhang⁶

¹Euronano, SIMaP-CNRS, Institut National Polytechnique de Grenoble, BP 75, Saint Matrin d'Heres campus 38402, France
²Kharkiv Polytechnical Institute, 61002 Ukraine
³Department of Physics, University of Ioannina, Ioannina 45110, Greece
⁴Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio 45433, USA
⁵Department of Materials Science and Metallurgy, Cambridge University, CB2 3QZ United Kingdom
⁶Beijing University of Aeronautics and Astronautics, Beijing 100083, People's Republic of China

1.Diffusion in metallic glasses: Analysis from the atomic bond defect perspective
Pages 3550-3557
A. Zhu, G.J. Shiflet and S.J. Poon

2.Alloy compositions of metallic glasses and eutectics from an idealized structural model
Pages 3613-3621
Ling-Ling Shi, Jian Xu and Evan Ma

Corrosion behavior of Fe-based ferromagnetic (Fe, Ni)–B–Si–Nb bulk glassy alloys in aqueous electrolytes

Z.L. Long^{a, b}, C.T. Chang^b, Y.H. Ding^a, Y. Shao^b, P. Zhang^a, B.L. Shen^b and A. Inoue^b

^aInstitute of Fundamental Mechanics and Material Engineering, Xiangtan University, Xiangtan, Hunan 411105, China

^bInstitute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan

Received 20 October 2007; revised 10 May 2008. Available online 21 July 2008.

Abstract

Fe-based ferromagnetic [(Fe_1−xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ (x = 0, 0.2 and 0.4) bulk glassy alloys (BGAs) with a diameter of 2 mm were prepared by copper mold casting. The corrosion behavior of glassy alloy rods obtained was investigated in 0.5 M NaCl, 0.5 M NaOH and 0.5 M H₂SO₄ aqueous electrolytes, respectively, using weight loss and electrochemical polarization measurements. It was found that the corrosion rates significantly decrease with an increase in Ni content in all examined solutions. The Ni-containing BGAs are spontaneously passivated with wide passive regions and low passive current densities in NaCl and NaOH solutions, but exhibit the active–passive–transpassive behavior in H₂SO₄ solution. The partial substitution of Ni for Fe results in a considerable improvement on the corrosion resistance of [(Fe_1−xNi_x)_0.75B_0.2Si_0.05]₉₆Nb₄ BGAs, because of the structural and chemical homogeneousness of the amorphous phase and the effect of Ni on promoting the formation of a passive film. Besides their high glass-forming ability (GFA), excellent soft-magnetic properties and good mechanical performance, which have been reported before, these FeNi-based BGAs also feature rather high corrosion resistance.

Glass-forming ability and mechanical properties of Ti-based bulk glassy alloys with large diameters of up to 1 cm

S.L. Zhu^a, X.M. Wang^a and A. Inoue^a

^aInstitute for Materials Research, Tohoku University, Aoba-ku Hirakata 2-1-1, Sendai 980-8577, Japan

Received 12 February 2008; revised 17 April 2008; accepted 29 May 2008. Available online 21 July 2008.

Abstract

Ti–Zr–Cu–Pd–Sn bulk glassy alloys have been synthesized by copper mold casting. The thermal properties, glass-forming ability (GFA) and mechanical properties were examined by differential scanning calorimetry (DSC), differential thermal analysis (DTA), X-ray diffractometry (XRD) and compression test. The series of bulk glassy alloys is expected to be used as biomedical materials because of the absence of toxic elements such as Ni, Al and Be. The 10 mm rods with full glassy structure can be obtained for the Ti₄₀Zr₁₀Cu₃₄Pd₁₄Sn₂ and Ti₄₀Zr₁₀Cu₃₂Pd₁₄Sn₄ alloys by copper mold casting. The Ti₄₀Zr₁₀Cu_36−xPd₁₄Sn_x (x = 0, 2, 4, 6) glassy alloys have a large supercooled liquid region of over 50 K. The Ti₄₀Zr₁₀Cu₃₄Pd₁₄Sn₂ bulk glassy alloy exhibits good plasticity of 3.5% during compressive applied load at ambient temperature in conjunction with distinct yield strain of 2.2% and high fracture strength of about 2050 MPa.