metallic glasses (amorphous alloys)shengguo.weebly.com/uploads/1/6/9/3/16931630/bmgs... · 2018-09-07 · Chalmers University of Technology Amorphous alloys/ metallic glasses An amorphous

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]


Outline

What are metallic glasses Historical development Alloy(composition) design strategy Unique properties Typical applications Scientific and technical challenges


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)


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


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)


Some histories

W Klement, R Willens, P Duwez, Non-crystalline Structure in Solidified Gold-Silicon Alloys, Nature, 1960, 187: 869

Au75Si25 P Duwez

Presenter

Presentation Notes

The purpose of the research program initiated in June 1959 was to obtain a solid solution in binary alloys of Cu and Ag. The fact that the CuAg phase diagram is a eutectic type is in contradiction to the generally accepted Hume-Rothery rules. Since the separation of the homogeneous liquid into Cu-rich and Ag-rich phases during cooling is a rate process, I thought that by cooling the melt very rapidly, the Cu and Ag atoms would not have time to cluster and would be forced into a nonequilibrium solid solution. An unexpected and surprising result however occurred when a quenched alloy containing 23 at. % Ge was found to be a hexagonal close-packed phase which does not exist in equilibrium. This was the first nonequilibrium crystalline phase obtained by liquid quenching, and since then more than 100 such phases have been reported. The next move was a lucky one leading to the first metallic glass. The alloy system Au-Si is very similar to Ag-Ge and it was expected that a hexagonal close-packed phase would also be obtained in Au-Si alloys. Instead the x-ray diffraction pattern of the quenched Au-20 at. % Si alloy indicated the absence of crystallinity.


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)


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


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)


Bulk Metallic Glasses

•From Liquidmetal Technologies

Structural


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)


Blow moulding of BMGs (Yale Schroers Lab)


SIM tray tool

BMGs and Apple products


Soft magnetic properties Soft magnetic materials: • High saturation magnetization • Low coercivity • High electrical resistivity

(Survanarayana, Bulk Metallic Glasses) amorphous transformer core

Presenter

Presentation Notes

In some magnetic materials, saturation is the state reached when an increase in applied external magnetic field H cannot increase the magnetization of the material further, so the total magnetic flux density B more or less levels off. (It continues to increase very slowly due to the vacuum permeability.) It is a characteristic particularly of ferromagnetic (and ferrimagnetic) materials, such as iron, nickel,cobalt and their alloys. In materials science, the coercivity, also called the magnetic coercivity, coercive field or coercive force, is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. An analogous property, electric coercivity, is the ability of a ferroelectric material to withstand an external electric field without becoming depolarized.


(Telford, Mater Today, 2014)

Seeing is believing I: high elastic strain


Seeing is believing II: excellent formability (Kumar et al., Nature, 2009)

upon crystallization


shear banding

Achilles heel: (Tension) Brittleness

(Inoue et al., Nat Mater, 2003)

(Cambridge web page)

Presenter

Presentation Notes

In Greek mythology, Achilles (/əˈkɪliːz/; Ancient Greek: Ἀχιλλεύς, Akhilleus, pronounced [akʰilːéu̯s]) was a Greek hero of the Trojan War and the central character and greatest warrior of Homer's Iliad. His mother was the nymph Thetis, and his father, Peleus, was the king of the Myrmidons. In Greek mythology, when Achilles was a baby, it was foretold that he would die young. To prevent his death, his mother Thetis took Achilles to the River Styx, which was supposed to offer powers of invulnerability, and dipped his body into the water. But as Thetis held Achilles by the heel, his heel was not washed over by the water of the magical river. Achilles grew up to be a man of war who survived many great battles. But one day, a poisonous arrow shot at him was lodged in his heel, killing him shortly after.


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)

Documents

metallic glasses (amorphous alloys)shengguo.weebly.com/uploads/1/6/9/3/16931630/bmgs... · 2018-09-07 · Chalmers University of Technology Amorphous alloys/ metallic glasses An amorphous