vidros metalicos

Introduction to metallic glassesGFA of metallic glasses

Mechanical propertiesOpen questions

Metallic Glasses and Bulk Metallic Glasses

D. Crespo1

1Departament de Fsica i Enginyeria NuclearUniversitat Politcnica de Catalunya

ETSEIB - 08/05/2008 Metallic Glasses and Bulk Metallic Glasses



Why metallic glasses?

(Loading ball_bounce_DSL.wmv)




Why not?

(W.H. Wang, Mat. Sci. Eng. R 2004)

Metallic glasses showoustanding mechanicalproperties.




Outline

1 Introduction to metallic glassesEarly developmentsProduction of bulk metallic glasses

2 GFA of metallic glassesStability of metallic glassesInfluence of the structure

3 Mechanical propertiesAlloys with unconventional propertiesElastic propertiesFracture of metallic glasses

4 Open questionsNew strategies for ductile BMGsPoly-amorphism?




Early developmentsProduction of bulk metallic glasses

Outline









The first amorphous metals.

Rapid solidification by melt spinning.

Metallic glasses are "newcomers" in theglass family.

1960 (Duwez et al.). First amorphousalloy: Au75Si25.Development of Rapid QuenchingTechniques (105 106K/s).1969 (Turnbull et al.). Well-defined glasstransition observed in some alloys.

Geometry limited by the high coolingrates.

Production of ribbons, lines and sheets.Applications as functional materials.





Metallic glasses at sight.

HRTEM of a crystalline metal. HRTEM of a metallic glass





Metallic glasses at sight.

XRD of several rare earth Bulk Metallic Glasses.

Wang, J. App. Phys. 99

(2006) 093506





Conventional metallic glasses.

Table: Values of Tg , and Tl for some typical marginal glass-formingcompositions.

Composition Tg (K) Tl (K)Fe80B20 600 1600Fe40Ni40B20 690 1030Pd80Si20 607 1070Zr65Be35 623 1238Zr50Cu50 670 1219Ni50Nb50 875 1350Au78Si8Ge14 293 629





Outline









Development of Bulk Metallic Glasses.

BMG: Metallic glasses with dimensions of mm.

1974 (Chen et al.) and 1982 (Duwez et al.). First Pd-Cu-Siand Pd-Ni-P bulk amorphous alloys.

Fluxing methods to inhibit heterogeneous nucleation.1989 (Inoue et al.). Exceptional glass forming ability ofRE-Al-(Cu,Ni) alloys.

Critical cooling rates




Development of Bulk Metallic Glasses.

Easier production methods for BMGs.

Rapid solidification by arc melting.

Lower cooling rates allow easierBMG production.

Arc melting.Suction casting.Severe deformation - Superplasticflow.





Bulk metallic glass compositions.

Table: Values of Tg , Tx and Tl of some representative BMG alloys.

Composition Tg (K) Tx (K) Tl (K)Zr46.75Ti8.25Cu7.5Ni10Be27.5 622 727 1185Zr41.2Ti13.8Cu12.5Ni10Be22.5 623 672 996Nd60Al10Ni10Cu20 438 478 755Pd40Ni10Cu30P20 576 656 836Pd40Ni40P20 590 671 991Ce70Al10Ni10Cu10 359 377 714La55Al25Ni20 491 555 941Mg65Cu25Y10 425 479 771Ca50Mg20Cu30 389 408 684





BMG alloys at present.

Parts of BMG produced at the Instituteof Physics of the Chinese Academy of Science

(W.H. Wang, Mater. Sci. Eng. R 2004)

New families constantly appearing.Use of common metals.Use of classical foundry productionmethods.

Commercial applications: Sportsgoods, jewelry, naval and warindustries.




Stability of metallic glassesInfluence of the structure

Outline









Glass formation ability (GFA).

Time-Temperature-Transformation diagram of glass forming

materials

The Time-Temperature-Transformatin diagram definesthe Glass Forming Ability of amaterial.

1: low cooling rates producecrystalline materials.2: critical cooling rate.3: fast cooling rates produceamorphous materials.

Traditional Silicate glasseshave very low critical coolingrates.





Amorphous metals with high GFA.

(W.H. Wang, Mat. Sci. Eng. R

2004)

(A. Inoue, Acta Mater. 2000)

Some BMG-alloys have GFA similar tosilicate glasses.

Best GFA is found in Pd40Ni10Cu30P20,with Rc = 0.10K/s and D = 10cm.Large supercooled liquid regionTx Tg = 135 K is found inZrTiCuNiBe alloys.

BMG-alloys allow to study viscosity,relaxation and diffusion in amorphousmetals.The factors influencing the GFA are notclearly determined.





Factors influencing GFA.

Confusion principle. Increase of GFA with the number ofelements.Inoues guiding principles.

Number of elements > 3.Differences in atomic radii > 12%Negative heats of mixing.

Inhibition of crystal nucleation. Kinetic and thermodynamiceffects.

I = AD exp[G

kT

], G =

16pi3

3 (Gls)2





Thermodynamic factors.

Gls = Hf SfTm TmT

C lsp (T )dT + TmT

C lsp (T )T

dT

Small heat of fusion (Dense packing).Large entropy of fusion(Multicomponent liquids).Rapid stabilization of Gls (T ) oncooling.

Small free volume in the liquid.Tendency to generate short rangeorder in the liquid state.





Kinetic factors.

Low mobility hinders crystalnucleation.

Viscosity of BMG-alloys at meltingpoint: 2 5 Pas.Viscosity of common metals atmelting point: 103 Pas.

Crystal nucleation and crystalgrowth are separated intemperature.





Kinetic factors.

What physical parameter can be related to the viscosity of aliquid? Fragility

In strong liquids (high fragility) follows an Arrhenius behaviour: = exp

( ERT ). Tend to be oftetahedral network structure.In fragile liquids (low fragility) departs from the Arrheniusbehaviour (Vogel-Tamman-Fulcher): = exp

( ER(TT0)

). Highly

coordinated ionic liquids, organicliquids.





Kinetic factors.

The viscosity behaviour near the glass transition classifyBMG as strong liquids.

Table: Values of the fragility parameter for metallic glasses.

Composition mZr46.75Ti8.25Cu7.5Ni10Be27.5 44Zr41.2Ti13.8Cu12.5Ni10Be22.5 50Nd60Al10Fe20Co10 33Pd40Ni10Cu30P20 59Pd40Ni40P20 54Pd77.5Si16.5Cu6 73Pt60Ni15P25 68La55Al25Ni20 35Mg65Cu25Y10 45





Outline









Structure of BMG-alloys. Common features.

Dense random packing.Differences with crystalline compounds ranging from 0.3%to 1%.

Local atomic order markedly different from the competingcrystalline phases.X-ray and neutron diffraction: No presence of pre-peak norsecond peak splitting.

Homogenous short range order and densely packedstructures.





Structure of Metal-Metal glasses.

Icosahedric clusters of less than 8 nm.Icosahedric configuration minimizes the volume of theatomic clusters but does not allow long range ordering.

Tendency to primary I-phase crystallization followed bysecondary crystallization of stable phases.Nucleation of stable phases requires long rangeredistribution in a densely packed icosahedral liquid.





Structure of Metal-Metalloid glasses.

(Fe,Co)80x (Nd,Nb)x (B,P)20 and similar glasses.Strong Metal-Metalloid bonding.Formation of network atomic configurations.Trigonal prisms connected by the "glue" atoms (Nb, Zr orLanthanides).





Structure of (Pd,Pt)-based glasses.

Coexistence of two cluster units.Pd-Ni-P cluster. Trigonal prismcapped with three half-octahedra.Pd-Cu-P cluster. Tetragonaldodecahedron.

The coexistence of the two cluster unitsdifficults rearrangement in crystallineorder.

Distinct GFA between PdNiP andPdNiCuP alloys.





GFA predictability.

Difficult determination of the structure for multicomponentmetallic glasses.The atomic structure has been resolved just in fewwell-known BMG compositions.New BMG-forming alloys are not predicted by the existingmodels.The formation mechanism and the main factors influencingGFA have not been clearly elucidated.




Alloys with unconventional propertiesElastic propertiesFracture of metallic glasses

Outline









Interesting structural properties.

Absence of microstructural features such as grains orphase boundaries. Possible use in small components.High hardness and high yield stress.High resilience and very low elastic loss coefficient.Fracture toughness can be very high.High viscosity of the liquid permits thermoplastic forming.





Unattractive structural properties.

Sever localization of plastic flow. Zero ductility in tension.Metallic glasses can be embrittled by aging and annealing.Fracture toughness can be very low.Instability above the crystallization temperature.





Outline









Measurement of elastic constants.

Experimental determination of theelastic constants, B (bulk modulus) andG (shear modulus), by acousticmeasurements.Mechanical spectroscopymeasurements.

Relaxation times can be calculated.It seems that an excess wing hasbeen detected in some metallicglasses.

Many of these measurements were notpossible in marginal glass-formingalloys.

Frequency dependence of the lossshear modulus of Ce-based BMG.Solid lines are fits using the KWWequation.

(X. F. Liu et al., J. Non-Cryst. Solids 2006)





Influence of structure on elastic constants.

The elastic constants of the glass are inherited from theinfinite frequency response of the liquid.

Shear modulus variation in the liquid and glassy states

Bulk modulus variation in the liquid and glassy states






The elastic constants of the glass are inherited from theinfinite frequency response of the liquid.

Shear modulus variation in the liquid and glassy states Bulk modulus variation in the liquid and glassy states






Densification increases the elasticconstants.Increase of pressure and structuralrelaxation give stiffer elastic constants.The B/G ratio (equivalently thePoissons ratio) increases underpressure and decreases after structuralrelaxation.

Decrease of B/G when reducing theatomic dispersion of the first RDFpeak.Increase of B/G when reducing themean atomic position ot the first RDFpeak.

Elastic moduli as a function of the meanatomic position s and the atomicdispersion of the first-neighbourshell. Calculation performed usinginteratomic pair potentials.

(E. Pineda, Phys. Rev. B 2006)





Relationship between elastic constants and fragility.

The origin of a broad correlationbetween fragility and Poissons ratiois debated at present.The elastic properties of the glassmay be linked with the viscositybehaviour of the liquid and so withthe GFA of the alloy.





Outline









Plastic deformation of amorphous metals.

Absence of dislocations.Increase of free volume duringhomogeneous deformation.Localization of plastic flow in shearbands.Heat release and temperature rise inshear bands.

Melting may be attained at shearbands.Nanocrystallization is observed atshear bands.





Fracture mechanism of amorphous metals.Shear bands are uncommon incrystalline solids but appear ingranular flows under high shear.

Hays et al. Phys. Rev. Lett. 84

(2000) 2901

Fig. 5. (a) Schematic of a plane strain biaxial compression test on drysand. (b) Axial compressive load P vs axial compressive displacement d.The point S marks the formation of a fully developed shear band.Han & Drescher, Soils and Found. 33

(1993) 118.





Fracture mechanism of amorphous metals.

Shear bands are uncommon in crystalline solids but appear ingranular flows under high shear.

NMR measurement of velocity in the gap of Couette Flow of 10% w/vcetylpyridinium chloride/sodium salicylate in brine.Holmes et al. Europhys. Lett. 64

(2003) 274 Hays et al. Phys. Rev. Lett. 84

(2000) 2901





Brittle-ductile bulk metallic glasses.

BMG may have high ductility incompression (Pt, Pd and Zr based).

Upto 20% of strain inPt57.5Cu14.7Ni5.3P22.5. (Schroers et al.,Phys. Rev. Let. 2004)

Ductile-brittle transition may occurby annealing below glass transition.

The same critical value ofPoissons ratio is found for differentalloys and different relaxationstates. (Lewandowski et al., Phil. Mag. Let. 2005)





Annealing of bulk metallic glasses.





Change of the structure during the deformationprocess.

Molecular dynamics simulationsand combination of the ReverseMonte Carlo method with elasticscattering measurements allowdetermination of local structures.The atomic configuration can bedescribed by means of relativefrequency of different Voronoipolihedra.






(M. Wakeda et al., Intermetallics 2006)

The decrease of free volume oncooling is related to the increment oficosahedral structures.The atomic rearrangement duringplastic strain leads to more freevolume and lower number oficosahedral environtments.The same structural features areresponsible of both the viscositybehaviour (and so GFA) in the liquidand the plastic flow in the glass.






Atomistic simulation of tensile deformation in Cu46Zr54 BMG.

(Ch. E. Lekka et al., Appl. Phys. Lett. 91

(2007) 214103)





Other interesting properties of BMGs.

Most of Fe based BMGs are soft magnetic materials

(A. Inoue et al., Acta Mat. 2004 52

1631)




New strategies for ductile BMGsPoly-amorphism?

Outline









Composite BMGs

BMG-dendrite compositescan be produced in Ti-Zralloys. The inhomogeneousmicrostructure with isolateddendrites in the BMG matrixstabilizes the glass againstcatastrophic failure due tounlimited extension of shearbands.High-resolution TEM images from the alloy DH1. a,Bright-field TEM micrograph showing a b.c.c.dendrite in the glass matrix. b, The correspondingdark-field micrograph of the same region. c, A highresolution micrograph showing the interface betweenthe two phases, with corresponding diffractionpatterns shown in the inset.Hofmann et al. Nature 451

(2008), 1085





Composite BMGs





Composite BMGs

Ashby plot. The BMG-basedcomposites have the highestfracture energies of all knownengineering materials.Hofmann et al. Nature 451

(2008), 1085





Outline









Polymorphism in crystalline structures

Polymorphism in materialsscience is the ability of asolid material to exist in morethan one form or crystalstructure.

Crystal packing of aspirin forms I (a), II (b), acetylgroup C-H O dimers (c), and S. L. Price predictedform II (d).Vishweshwar et al. J. Am. Chem. Soc., 127 (2005),16802





Polymorphism in a metallic glass

In-situ X-Raydiffraction ofCe55Al45 metallicglass

XRD-patterns of the Ce55Al45metallic glass in a diamondanvill cell.Sheng et al. Nature 6

(2007)

192






In-situ X-Ray diffraction ofCe55Al45 metallic glass

Specific volume versus pressure for amorphousCe55Al45.Sheng et al. Nature 6

(2007) 192






In-situ X-Raydiffraction ofCe55Al45 metallicglass

Comparison of the structurefactors for the two amorphouspolymorphs of Ce55Al45 atcomparable pressures.Sheng et al. Nature 6

(2007)

192






In-situ X-Ray diffractionof Ce55Al45 metallicglass

Comparison of spin-resolved electrondensity of states (DOS), obtained for thetwo amorphous Ce55Al45 phases.Sheng et al. Nature 6

(2007) 192





Summary

Bulk metallic glasses have high GFA and large stabilityagainst crystallization. They allow the study of glasstransition phenomena in metallic-bonding systems.Application of BMG as structural materials requiresimprovement of the GFA and the mechanical properties.The atomic structure features influencing GFA may alsodetermine the elastic response and the brittle-ductilebeaviour of metallic glasses.Better knowledge of the atomic structure and its evolutionduring the glass transition and the plastic deformationprocess is crucial for BMG development.


Introduction to metallic glassesEarly developmentsProduction of bulk metallic glasses

GFA of metallic glassesStability of metallic glassesInfluence of the structure

Mechanical propertiesAlloys with unconventional propertiesElastic propertiesFracture of metallic glasses

Open questionsNew strategies for ductile BMG'sPoly-amorphism?

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