材料科学新进展_英文课程课件_Amorphous metals_2015

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Physics Today Feb.(2013)32
Amorphous alloys
Intensity (cps)
Features of amorphous alloys

Introduction---Structure features
800 600 400 200 0 20 30 40 50 60 70 80 90 100
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Amorphous alloys
High corrosion resistance of BMGs
Properties : Corrosion behavior
Structurally homogeneous
Chemically homogeneous
No dislocation, distortions, grain boundaries, fault, phase boundaries and so on
Amorphous alloys
Amorphous Alloys
(Metallic Glasses)
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Amorphous alloys
What is metallic glass (MG)?
Metallic species “frozen” in amorphous glassy state. When a liquid is cooled below its melting temperature TM…… Typically, as the supercooled liquid’s temperature decreases, so do its enthalpy and volume. At what’s known as the glass transition temperature TG, the atoms in the liquid become so tightly packed that they can no longer easily rearrange themselves. In that glassy state, the system behaves like a solid, although liquid-like disorder is “frozen” into its structure. The challenge, then, is to supercool the liquid from TM to TG so fast that there’s no chance for a crystalline phase to nucleate and grow.
The BMG specimen with a large elongation in the supercooled liquid region
J Non-crys Solids 351(2005)209
A large elongation for La55Al25Ni20 BMG (15000%)
Long-range disorder No grain boundaries Short-range order Isotropy
2(degree)
X-ray Diffraction, XRD
5 nm
High Resolution TEM
Selected Area Electron Diffraction
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Amorphous alloys
Representative BMGs
Pd40Ni40P20 25mm D. Turnbull et al.,1984
Prof. David Turnbull
formerly with Harvard University
Pd40Cu30Ni10P20 72 mm A. Inoue et al.,1997
ductile dendrite Ductile metal reinforced BMG matrix composites were prepared via in situ processing The dendritic crystalline phases serve as sites for the initiation of shear bands and confines the propagation of shear bands, leading to the large plasticity for the composite Phys. Rev. Lett. 84(2000)2901
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Acta Materialia 48 (2000) 279
Amorphous alloys
Properties : Mechanical properties
How to avoid premature failure and enhance the compressive plasticity of BMGs?
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Supercooled liquid region
Amorphous alloys
What is metallic glass (MG)?
Formation of metallic glasses by cooling of the melt was first accomplished in 1960 by Duwez by rapid solidification First metallic glasses were binary metallic alloy melts Problem at the time : Extremely high cooling rates (~106 K/sec) were needed. Thickness limited to m ribbons Crystal： Long-range order Grain boundaries (Slow cooling)
Liquid： Random arrangement
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Amorphous alloy: No long-range order No grain boundaries (Fast cooling)
Amorphous alloys
What is metallic glass (MG)?
Any liquid will vitrify, or solidify into a glass, if it’s cooled rapidly enough. Nowadays we know that many alloys can form glasses when cooled at rates below 1000 K/s and as low as 1 K/s. The bulkier a sample is, the more slowly its interior cools. The critical cooling rate required for glass formation also determines the critical casting thickness—the maximum thickness for which the sample can be glass throughout. One can speak of a material’s glass-forming ability (GFA) as being either inversely proportional to its critical cooling rate or proportional to its critical casting thickness. A bulk metallic glass (BMG) is a metal with a critical casting thickness of at least 1 mm.
Mg Ca Sc Ti Y Zr La Hf Fe Co Ni Cu Pd Pt Au
Al
Ce Pr Nd
Sm
Gd
Dy Ho Er Tm
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2015-3-15
Amorphous alloys
Atomic packing in metallic glasses
Ni La Ni La
La Ni
Al89La6Ni5
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Armor-piercing projectile
Amorphous alloys
The deformation is inhomogeneous at room temperature: the strain is localized within a few thin shear bands. The deformation is homogeneous at high temperature, i.e. at supercooled liquid region
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Prof. Akihisa Inoue
Tohoku University
Amorphous alloys
Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 25mm D. Turnbull et al.,1984
California Institute of Technology
Prof. W.L. Johnson
Residual stress Confined deformation ………………
How to achieve tensile ductility？
BMG-matrix composites
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Amorphous alloys
In situ composites
Apparent work hardening; Total strain of 8%
No secondary phase elements, fluctuation component, segregation, and so on.