SYNTHESIS AND CONSOLIDATION

OF NANOPOWDERS: APPROACHES AND METHODS

Cracow, 2014

Michail Alymov

ISMAN

Outline

1. Introduction.2. Synthesis of nanopowders.3. Processing of bulk nanostructured materials. 3.1. Consolidation of nanopowders. 3.1.1. Pressing at room temperature. 3.1.2. Sintering without pressure. 3.1.3. Sintering under pressure.4. Properties of consolidated nanomaterials.5. Summary.

Classification of nanomaterials

1. Powders.

2. Layers and coatings.

3. Composite materials.

4. Bulk materials.

Powder metallurgy = synthesis of powders + consolidation of powders.By powder metallurgy methods we can produce all kinds of nanomaterials.

R.W. Siegel, Proc. Of the NATO SAI, 1993,v.233, р.509

Methods Technologies Materials

Powder metallurgy Consolidation of nanopowders:

Pressing and sintering,

Pressure sintering

Metals and alloys, ceramic, metal-ceramic, composites, polymers

Crystallization from amorphous state

Crystallization of amorphous alloys,

Consolidation of amorphous powders with further crystallization

Metallic materials

able to bulk amorphisation.

Severe plastic deformation

Equal channel angular pressing,

Torsion under high pressure,

Multiple all-round forging.

Metallic materials

Nanostructurisation by precision heat treatment and thermomechanical treatment

Heat treatment.

Thermomechanical treatment

Metallic materials

METHODS FOR PROCESSING OF BULK NANOSTRUCTURED MATERIALS

PressureTemperature

Time

Powder

Size of Ni particles = 70 nm

Bulk material

Grain size = 100 nm

Hydroxyapatite ceramics from nanopowders

Pressure 3 GPaSintering temperature 670°С

Grain size 35-50 nmMicrohardness 5,8 GPa

Fomin A.C., Barinov C.M., Ievlev V.М. a.o. 2008.

After pressing After sintering

Methods for synthesis of nanopowders

– SHS (self-propagating high temperature synthesis), – chemical – metallurgical method- plasma-chemical synthesis – mechanical alloying - electrical explosion of wires - vaporization-condensation technique - flowing gas evaporation technique - vapor phase synthesis – cryochemical synthesis - sol-gel method - hydrothermal synthesis and others

There are many methods for synthesis have been developed to produce nanopowders. The synthesis routes are diverse and result in nanoparticles with a range of characteristics, such as size, size distribution, morphology, composition, defects, impurities, and agglomeration (“soft” and “hard”). By now, several tens of methods have been developed for the synthesis of metallic, ceramic, cermet, and other nanopowders. Each method is characterized by its own advantages and disadvantages. Some methods are reasonably used for the preparation of metal powders, while other methods are useful for ceramic powders.

The ratio between the average particle size and performance of methods

0 200 400 Size of particles, nm

200

0

400

Levitation-jet

method

EEW

4

Plasma-chemical

Chemical and metallurgical

800SHS

Calcium-hydride method

Evaporation-condensation

Alymov M.I. Composites and Nanostructures, 2012, v.3.

METHODS for the NANOPOWDERS CONSOLIDATION

Uniaxial pressing: static, dynamic, vibration

Isostatic pressing

Extrusion

Sintering under pressure

Spark plasma sintering

Sock wave pressing

Severe plastic deformation

Features of the nanopowders consolidation

Impurities play an important role in densification.

Agglomeration of nanoparticles into clusters.

Low dislocation density.

The possibility of new or different mechanisms of densification.

Diffusion-induced grain-boundary migration and boundary-energy-induced rotations may alter densification mechanisms.

Cold pressing - uniaxial (static, dynamic, vibrational),

- multiaxial (hydrostatic, gasostatic),

- severe plastic deformation,

- cold rolling.

Influence of average iron particle diameter on the density of compacts

M.I. Alymov, 1990

0 0,4 0,8 1,2 1,6 Pressure, GPa

100

60

20

Rel

ativ

e d

ensi

ty, %

23 nm

26 nm28 nm

60 nm

120 nm

1 mkm40 mkm

Diameter of dislocation free iron particle is equal to 23 nm

The friction between the nanoparticles substantially affects the densification of nanopowders. The contribution of plastic deformation to the densification of nanopowders is insignificant since the nanoparticles are free from dislocations and they cannot be deformed as coarse particles due to the movement of dislocations.

Consolidation process of nanopowders is strongly affected by:

- particle size distribution,

- concentration of impurities,

- surface conditions,

- particle shape,

- pressing technique.

Sintering mechanisms

1 - surface diffusion, 2 - volume diffusion from surface, 3 - vapor transport from surface,4 - grain boundary diffusion, 5 - volume diffusion, 6 – dislocation diffusion

Alymov M.I., Letters on Materials. 2013.

Sintering of gold

nanoparticles

Influence of pressure on sintering

Sintering temperature

100

Den

sity

, %

Sintering under pressure

90

80

70Т1

Sintering without pressure

Т2 < Т1

d1d2 < d1

Equipment for the sintering under the pressure

thermocouple

bellows

entrance of gas

sample

anvil

yield of gas

vessel

heating element

punch

padding

Pressure

Pressure sintering of iron nanopowder

400 500 600 700 800 Temperature, °С

100

Den

sity

, %

380 MPa

90

80

70

60

0 MPa

90 MPa

280 MPa

М.И. Алымов, ФХОМ, 1997

Influence of the mode of deformation on sintering

HIP – pressing in dies – forging – extrusion - ECAP

Hydrostatic component of pressure

Tangential component of pressure

Gas extrusion method

gas

chamber

sample

diedie block

Compacts of iron and nickel nanopowder after extrusion

Iron

Nickel

10 cm

Nickel nanopowder green compact after hydrostatic pressing

TEM microstructure image of nickel nanopowder compact after hot forging

Grain size near 70 nm

MECHANICAL PROPERTIES OF THE COMPACTS

Method Material Particle size, mkm

Grain size, mkm

в ,MPa

, %

Hot isostatic pressing

Ni

6 25 440 36

0,06 1 545 7

Fe

40 55 350 41

0,04 1 460 1

Extrusion Ni 0,06 0,1 700 15

Mechanical properties of nanocrystalline and coarse-grained nickel

Nano-grained Coarse-grained

, MPa 530 80

B , MPa 625 400

, % 22 40

ψ, % 19,5 -

Kc , MPa∙m1/2 82,3 51,7

Toughness, J/cm2 63-66 198-203

The crack growth resistance for nanocrystalline Ni is on 30% higher the crack growth resistance coarse grained Ni.

Ni

Valiev R. 2001

Fe

Cu

Ult

imat

e st

ren

gth

, M

Pa

Relative elongation , %

Hardness of WC-8%Co hard alloy depends on the size of WC-grain

0 0,5 1,0 1,5 2,0 Size of WC-grain, mkm

Har

dn

ess

HV

, GP

a

14

16

18

20

22

24

26

Alymov M.I. a.o. Composites and Nanostructures. 2012.

SHS pressure sintering

3

4

21

Sherbakov V.А.

1 - tungsten spiral initiating the SHS reaction

2 - tablet from powders of the initial reactants

3 - insulating porous medium (sand);

4 - mold.

Before SHS extrusion

Stolin A.M.

Initial charge billets

Form of a matrix

Ignition system

The mold assembly

Guide caliber

After SHS extrusion

Stolin A.M.

Material after SHS (press residue)

Extruded material (finished product)

Effectiveness for bulk nanopowder materials

Materials EffectivenessHard alloys Increase of hardness by a factor of 5-7

High strength steels and alloys Increase of strength by a factor of 1,5-2

Ceramic materials Formability as for titanium alloys

Nanopowder materials with special properties

Mechanical, chemical, optical and other properties

Wear resistance coatings Increase of resistance by a factor of 170

Thank you for your attention

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