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Thứ năm, 19 Tháng tư 2007 |
 Published in the July 1998 issue.There's only one easy way to drop five to eight strokes off your golf score--skip the last hole. But even in friendly games, that's not an option. As a result, golfers continue to fall for two of the biggest marketing scams around. The first is the "No-Matter-What-You're-Doing-It's-Wrong" instructional video (usually hosted by some paunchy guy you've never heard of). The second is the purported technological advancement that's actually a useless gizmo dreamt up by some crackpot who bought a home shop instead of a lottery ticket.
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Thứ năm, 19 Tháng tư 2007 |
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Figure of disorganized elements: In this simulated mixture of elements, the investigators have added small amount of the large element Yttrium to prevent crystal formation and facilitate metallic glass production. | | 
In this figure, two different elements are arranged to form a crystalline lattice structure like that found in an ordinary metal. |
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Thứ năm, 19 Tháng tư 2007 |
 ORIGINATING TECHNOLOGY/ NASA CONTRIBUTION
In the same way that the inventions of steel in the 1800s and plastic in the 1900s sparked revolutions for industry, a new class of amorphous alloys is poised to redefine materials science as we know it in the 21st century.
Welcome to the 3rd Revolution, otherwise known as the era of Liquidmetal® alloys, where metals behave similar to plastics but possess more than twice the strength of high-performance titanium. Liquidmetal alloys were conceived in 1992, as a result of a project funded by the California Institute of Technology (CalTech), NASA, and the U.S. Department of Energy, to study the fundamentals of metallic alloys in an undercooled liquid state, for the development of new aerospace materials. Furthermore, NASA’s Marshall Space Flight Center contributed to the development of the alloys by subjecting the materials to testing in its Electrostatic Levitator , a special instrument that is capable of suspending an object in midair so that researchers can heat and cool it in a containerless environment free from contaminants that could otherwise spoil the experiment. |
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Thứ ba, 17 Tháng tư 2007 |
The strength of a material is assessed most often by means of a tensile test. For a given material with an original cross-section area A0, if the applied maximum tensile force is equal to Fmax, the fracture strength can be calculated by δF=Fmax/A0, as described in the textbooks.[1,2] For a bulk metallic glassy specimen, it often fails in a shear mode, as shown in Figure 1, and the shear fracture surface makes an
angle of ΘT =56° with respect to the tension axis. Such shear fracture behavior has been widely observed in many metallic glasses, as summarized in the literatures[3,4] and Table 1.[5–14] According to the definition in the textbooks,[1,2] the tensile fracture strength of the metallic glass should be equal to rT=Fmax/A0. However, the actual area of the shear fracture surface becomes A0/sin(ΘT) and the applied normal tensile force on the shear plane is Fmax cos(hT), as shown in Figure 1. This will result in another tensile strength Fmaxsin(ΘT)cos(ΘT)/A0, which is different from that (Fmax/A0) defined in textbooks.[1,2] Consequently, this gives rise to some interesting and significant questions. Which is the real tensile strength of a metallic glass, Fmax/A0 or Fmaxsin(ΘT)cos(ΘT)/A0? Why do metallic glasses often fail neither along the maximum normal stress plane (ΘT =90°) nor along the maximum shear stress plane (ΘTT =45 °) under tensile loading[5–14]? What is the physical nature of the materials strength? |
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Thứ hai, 16 Tháng tư 2007 |
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HIROTSU, Yoshihiko and MATSUBARA, Eiichiro Group
MIZUTANI, Uichiro Group
FUKUNAGA, Toshiharu Group
MORI, Hirotaro Group
The main research topics of A02 division are as follows: (1) structure analysis of as-formed and supercooled liquid states of metallic glasses by high-resolution electron microscopy and electron diffraction, and synchrotron X-ray radiation; (2) evaluation of electronic structures of metallic glasses and related compounds by X-ray photo-emission spectroscopy (XPS) and band-structure calculation; (3) analysis of atomic structures and dynamics of metallic glasses by neutron scattering; and (4) direct observation of the glass transition from liquid to glass state on an atomic scale using in-situ high-resolution TEM. |
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Thứ hai, 16 Tháng tư 2007 |
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 An amorphous metal is a metallic material with a disordered atomic-scale structure. In contrast to most metals, which are crystalline and therefore have a highly ordered arrangement of atoms, amorphousglasses", and so amorphous metals are commonly referred to as "metallic glasses" or "glassy metals". However, there are several other ways in which amorphous metals can be produced, including physical vapor deposition, solid-state reaction, ion irradiation, and mechanical alloying. Amorphous metals produced by these techniques are, strictly speaking, not glasses, but materials scientists commonly consider amorphous alloys to be a single class of materials, regardless of how they are prepared. alloys are non-crystalline. Materials in which such a disordered structure is produced directly from the liquid state during cooling are called "
Bulk metallic glasses (BMG) are amorphous metals with critical cooling rates low enough to allow formation of amorphous structure in thick layers (over 1 millimeter). |
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Thứ hai, 16 Tháng tư 2007 |
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> Download Full Paper < It was a long-cherished dream for materials scientists to find a nearly ideal metallic alloy with high strength and super-plasticity concurrently as a super-material both extremely strong and exceptionally hard for human use. Due to the limitation of the deforming mechanism, a material's plasticity usually has to turn down or even to disappear when its strength is raised. This is because the same properties that give metallic glasses their strength also contribute to their propensity to fracture. |
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Thứ hai, 16 Tháng tư 2007 |
Prof. Todd C. Hufnagel (more information! )
Department of Materials Science and Engineering
Johns Hopkins University
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Thứ ba, 10 Tháng tư 2007 |
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Bài viết này được biên dịch bởi Nguyễn Hoàng Việt, NCS tại Nano-particulate Materials Processing, UOU, Hàn Quốc. Nguyên tác:Metallic glasses - Historical background của tác giả P. Duwez Vào thời điểm cuốn sách này được xuất bản (1981) cách đó 20 năm, lúc mà các băng rất mỏng đầu tiên về thủy tinh kim loại được tạo ra. Thực ra là tháng 11 năm 1959, khi 1 chương trình nghiên cứu con mà mục đích của nó là khác xa về tạo ra thủy tinh kim loại, hợp kim có chứa 75%Au và 25%Si được nguội nhanh từ trạng thái lỏng đã hình thành thể vô định hình. |
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