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Chalmers University of Technology
A brief introduction to metallic glasses (amorphous alloys)
Sheng Guo Assistant Professor
Materials and Manufacturing Technology Department Chalmers University of Technology
E-mail: [email protected]
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Chalmers University of Technology
Outline
What are metallic glasses Historical development Alloy(composition) design strategy Unique properties Typical applications Scientific and technical challenges
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Chalmers University of Technology
Amorphous alloys/ metallic glasses An amorphous metal, also known metallic glass or glassy metal, is a solid metallic material, usually an alloy, with a disordered atomic-scale structure.
Amorphous materials, like window glass o have no long-range order, so no translational symmetry o not truly random, have short-range order
(Cambridge Univ. TLP library) (Telford, Mater Today, 2014)
(Kaban et al., Acta Mater, 2013)
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Chalmers University of Technology
Signs for amorphism
High-resolution TEM (halo)
(Li et al., J Alloy Compd, 2010)
Differential scanning calorimetry (Tg) (Karpukhina et al., Chem Soc Rev, 2014)
X-ray diffraction (hump)
(Lacasse et al., Pfonline.com)
o have no long-range order/translational symmetry o shows the glass transition behavior
amorphous
amorphous
amorphous
crystalline crystalline
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Chalmers University of Technology
Some concepts
* Glass transition
(Debenedetti et al., Nature, 2001)
* Supercooled liquid region: ∆T=Tx-Tg
A gauge of thermal stability of metallic glasses, also quite often characterizes the glass forming ability
(Zhang et al., Mater Trans, 1990)
* Critical cooling rate
(Cornell web page)
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Chalmers University of Technology
Some histories
W Klement, R Willens, P Duwez, Non-crystalline Structure in Solidified Gold-Silicon Alloys, Nature, 1960, 187: 869
Au75Si25 P Duwez
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Chalmers University of Technology
MGsBulk Metallic Glasses (BMGs)
Pd42.5Cu30Ni7.5P20 BMG
Φ80*85 mm
(Nishiyama et al, Intermetallics, 2012)
melt spinning
3.4 Kg!
BMGs: the smallest dimension of
MGs>1mm
(Telford, Mater Today, 2014) (Wikipedia)
suction casting (Survanarayana, Bulk Metallic Glasses)
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Chalmers University of Technology
A Inoue (1990) Inoue’s three empirical rules to prepare BMGs at least 3 alloying elements; large mismatching atomic sizes of constituent elements large negative heat of mixing among major alloying elements
Alloy design strategy for BMGs
(Greer, Mater Today, 2009) (Lu et al., J Mater Sci, 2004) (Guo et al., Intermetallics, 2013)
atomic size distribution heat of mixing
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Chalmers University of Technology
Attractive properties of BMGs
High strength : >2000 MPa High hardness: 600-1300 DPH High fracture toughness: >70 MPa . m1/2
High elastic strain: ~ 2% elastic strain Good formability: >1000% elongation Superior aqueous corrosion resistance Good wear resistance Excellent soft magnetic properties: Fe-base MGs Other interesting optical and physical properties
(Demetriou et al, Nat Mater, 2011)
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Chalmers University of Technology
Bulk Metallic Glasses
•From Liquidmetal Technologies
Structural
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Chalmers University of Technology
Micro-devices: micro-gears made of MGs Only one casting process
100µm
Super-precision gear mold Super-precision gear parts made of glassy alloy
Newly developed gear
Diameter = 647 mm Teeth = 14 p Module = 40 mm
Conventional machined gear
Diameter = 288 µm Teeth = 9 p Module = 25 µm
Human hair (d= 80 µm )
(Nishiyama et al, 2005)
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Chalmers University of Technology
Blow moulding of BMGs (Yale Schroers Lab)
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Chalmers University of Technology
SIM tray tool
BMGs and Apple products
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Chalmers University of Technology
Soft magnetic properties Soft magnetic materials: • High saturation magnetization • Low coercivity • High electrical resistivity
(Survanarayana, Bulk Metallic Glasses) amorphous transformer core
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Chalmers University of Technology
(Telford, Mater Today, 2014)
Seeing is believing I: high elastic strain
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Chalmers University of Technology
Seeing is believing II: excellent formability (Kumar et al., Nature, 2009)
upon crystallization
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Chalmers University of Technology
shear banding
Achilles heel: (Tension) Brittleness
(Inoue et al., Nat Mater, 2003)
(Cambridge web page)
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Chalmers University of Technology
Glass transition is still a mystery
“What is the nature of glassy state?” was selected as one of the most important 125 scientific questions to be resolved this century--- Science, 2005
“Glass transition is one of the deepest and most important unsolved problems in condensed matter physics” ---- Nature Materials, 2008
(Debenedetti et al., Nature, 2001)