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[资源] 【资源】非晶合金最新文献--10

1。Flow serration and shear-band propagation in bulk metallic glasses

H. M. Chen,1 J. C. Huang,1 S. X. Song,2 T. G. Nieh,2 and J. S. C. Jang3
1Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung, Taiwan 804, Republic of China
2Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
3Department of Materials Science and Engineering, I-Shou University, Kaohsiung, Taiwan 840, Republic of China

Flow serration in bulk metallic glasses (BMGs) was analyzed using high-sensitivity strain gauges. Based on the displacement-time profile for one serration, shear-band propagating speed was determined and found to be insensitive to the applied strain rates. The disappearance of serration at high strain rates is a result that the signal of displacement burst was overwhelmed by the applied strain rate. In comparison with the ductile Pd-based and brittle Mg-based BMGs, the ductility of BMGs appears to be closely related to the dynamics during shear-band propagation. ©2009 American Institute of Physics

2。Synchrotron X-ray Scattering Investigations of Oxygen-Induced Nucleation in a Zr-Based Glass-Forming Alloy

J.J. Walla, J.D. Almerb, S.C. Vogela, P.K. Liawc, H. Chooc, d and C.T. Liuc, d

aLANSCE-LC, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
bAdvanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA
cDept. of Mater. Sci. and Eng., The University of Tennessee, Knoxville, TN 37996, USA
dMater. Sci. and Tech. Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

Received 6 February 2009; revised 2 April 2009; accepted 3 April 2009. Available online 9 April 2009.

Abstract
The metallic glass forming alloy VIT-105 (Zr52.5Cu17.9Ni14.6Al10Ti5) was used to study the effect of oxygen on nucleation. Ex-situ synchrotron x-ray scattering experiments performed on as-cast samples showed that oxygen leads to the formation of tetragonal and/or cubic phases, depending on oxygen content. The samples crystallized into either a primitive tetragonal phase or the so-called FCC “big cube” phase in a glassy matrix. A subsequent discussion on the role of oxygen in heterogeneous nucleation in Zr-based bulk metallic glasses is presented.

3Toughness of as-cast and partially crystallized composites of a bulk metallic glass

R. Raghavana, b, V.V. Shastrya, A. Kumarc, T. Jayakumarc and U. Ramamurtya

aDepartment of Materials Engineering, Indian Institute of Science, Bangalore 560012, India
bEMPA Materials Science and Technology, Feuerwerkerstrasse 39, CH-3602 Thun, Switzerland
cNondestructive Evaluation Division, Indira Gandhi Center for Atomic Research, Kalpakkam 603102, India

Received 19 January 2009; revised 3 March 2009; accepted 11 March 2009. Available online 11 April 2009.

Abstract
The deformation and fracture response of a bulk metallic glass (BMG) post-annealing above the glass transition temperature is examined. The toughness of the glass-matrix composite exhibits a sharp transition beyond a critical volume fraction of crystallization to values as low as that of brittle silicate glass. Instrumented indentation tests supplemented by impact tests were used to study this ductile to brittle transition exhibited by the partially crystallized samples. Indentation on the anneal-embrittled specimens shows lateral cracks in addition to cracks along the corners. The applicability of the Poisson's ratio-toughness correlation with respect to partially crystallized samples is also investigated.

4。Effects of ion implantation on surface structures and properties for bulk metallic glass

Yuan Zheng Yanga, Ping Jun Taoa, Guo Qing Lib, Zhong Xin Mub, Qiang Ruc, Zhi Wei Xiea and Xian Chao Chena

aFaculty of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China
bState Key Laboratory for Materials Modification, Dalian University of Technology, Dalian 116024, China
cSchool of Physics and Communication Engineering, South China Normal University, Guangzhou 510006, China

Received 8 December 2008; revised 7 February 2009; accepted 19 February 2009. Available online 11 April 2009.

Abstract
A plate-like Zr55Cu30Ni5Al10 bulk metallic glass (BMG) was prepared and Co ion implantation was carried out. The effects of ion implantation on surface structures and properties of the BMG have been studied. The results showed, after Co ion implantation, the BMG specimen still maintained an amorphous structure on the whole. Ion implantation changed the thermodynamic parameters and enhanced the thermal stability of the amorphous alloy. Along the depth direction, cobalt element implanted basically existed in a metal state. The maximum enhancement of surface micro-hardness was about 103 Hv or 18%. The average friction coefficients before and after ion implantation were 0.331 and 0.168, respectively, and the corresponding grinding trace widths were 80.23 and 60.17 μm, respectively, i.e., the Co ion implantation has reduced the average friction coefficient and corresponding grinding trace width by about 52.3% and 32.68%, respectively. The reasons of efficient improving the surface performances by ion implantation surface modification in BMG were analyzed and discussed.

5。Flow serration and shear-band viscosity during inhomogeneous deformation of a Zr-based bulk metallic glass

S.X. Songa and T.G. Nieha

aDepartment of Materials Science and Engineering, The University of Tennessee, 420 Dougherty Building, Knoxville, TN 37996, USA

Received 28 December 2008; revised 16 February 2009; accepted 5 March 2009. Available online 10 April 2009.

Abstract
Uniaxial compressive behavior of Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass at room temperature was characterized with high-sensitivity strain gauges directly attached to test samples. Displacement–time curves exhibited micron-size serrations (or bursts) after the onset of yielding, apparently associated with discrete shear band formation. Each displacement burst disclosed three-step (acceleration, steady-state, and deceleration) process in shear band propagation. The viscosity of a propagating shear band was found to be relatively low and, actually, in a similar range usually measured in the supercooled liquid region. A detailed analysis of the experimental results using a self-consistent Vogel–Fulcher–Tamann (VFT) equation based on free volume model suggested that shear band propagation was mainly resulted from free volume accumulation.

6。Defects on Corrosion of Zr-Based Metallic Glasses

B. Vishwanadh1, Geogy J. Abraham1, Jagannath1, S. Neogy1, R. S. Dutta1 and G. K. Dey1

(1) Bhabha Atomic Research Centre, Trombay, Mumbai, 400-085, India

Abstract X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed a fully amorphous structure for as-cast bulk metallic glass (BMG) and melt-spun ribbons of Zr52Ti6Al10Cu18Ni14 prepared by copper mold casting and the melt-spinning technique, respectively. For melt-spun ribbons, the wheel-side surface contained a higher concentration of quenched-in defects (air pockets), whereas surface irregularities were noticed in the air side. Fluctuation microscopy indicated more medium-range order for the as-cast structure of BMG than for the melt-spun ribbon, whereas in the BMG, the medium-range order was located more in the central region than in the periphery. Macro- and microcell electrochemical experiments of the BMG along the cross section and macrocell experiments of each side of the ribbons in dilute acidic chloride environments indicated that the corrosion resistance of the BMG decreased with the increase in the medium-range order; the medium-range order, however, was less deleterious than either the surface irregularities or the quenched-in defects from the viewpoint of corrosion. A surface film formed on the metallic glasses in a dilute acidic chloride environment mainly consisted of oxide of zirconium, in which zirconium was present in the Zr+3, Zr+2, and Zr+1 state in the BMG and in the air-side and wheel-side surfaces, respectively.

7。Extrusion properties of a Zr-based bulk metallic glass
G.S. Yu a, J.G. Lin a,⁎, W. Li a,⁎, C.E. Wen b
a Faculty of Material and Photoelectronic Physics, Key Laboratory of Low Dimensional Materials and Application Technology (Ministry of Education), Xiangtan University,
Hunan, Xiangtan 411105, China
b Centre for Material and Fibre Innovation, Deakin University, Pigdons Road, Geelong, Victoria 3217, Australia

The extrusion behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formabilitywas observed under lowstrain rates at temperatures higher than 395 °C.
The metallic glasses were fully extruded without crystallization and failure within the range of T=395–415 °C
under strain rates from5×10−3 s−1 to 5×10−2 s−1, and the deformation behavior of themetallic glasses during
the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0.

8.Characteristics of near-eutectic and off-eutectic Zr-Al-Ni-Cu glass forming alloys
An-hui. Cai1, 2*, Xiang Xiong1,Yong Liu1, Jiang-hong Li1, Wei-ke An2 and Yun Luo2
1 State Key Laboratory of Powder Metallurgy, Central South University, Changsha, 410083, P.R. China
2 Department of Mechanical and Electrical Engineering, Hunan Institute of Science and Technology,
Yueyang, 414000, P.R. China
Abstract: The glass forming ability (GFA) and behavior of glass transition and onset crystallization for
near-eutectic and off-eutectic Zr-Al-Ni-Cu metallic glasses were investigated by non-isothermal test. The
results show that, as for near-eutectic alloy, the glass transition temperature Tg is more sensitive to the
heating rate than the onset crystallization temperature Tx. The apparent activation energy of glass transition
Eg is greater than that of onset crystallization Ex, and the greatest among metallic glasses studied. Its critical
cooling rate Rc is the lowest among metallic glasses studied. Moreover, the further the distance from
near-eutectic composition, the larger is the Rc for glass forming alloy.

[ Last edited by hslining on 2009-9-12 at 09:05 ]

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