Transcript Document

Cracow, 2014
SYNTHESIS AND CONSOLIDATION
OF NANOPOWDERS:
APPROACHES AND METHODS
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 FOR PROCESSING OF BULK
NANOSTRUCTURED MATERIALS
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 Heat treatment.
by precision heat
Thermomechanical treatment
treatment and
thermomechanical
treatment
Metallic materials
Bulk material
Powder
Pressure
Temperature
Time
Size of Ni particles = 70 nm
Grain size = 100 nm
Hydroxyapatite ceramics from nanopowders
After pressing
Pressure 3 GPa
Sintering temperature 670°С
After sintering
Grain size 35-50 nm
Microhardness 5,8 GPa
Fomin A.C., Barinov C.M., Ievlev V.М. a.o. 2008.
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
Capacity, g/h
800
SHS
400
Calcium-hydride
method
Plasmachemical
200
EEW
Levitation-jet
Chemical and
metallurgical
4
method
0
Evaporationcondensation
0
200
400
Size of particles, nm
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 boundaryenergy-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
100
Relative density, %
40 mkm
1 mkm
120 nm
60 nm
28 nm
26 nm
60
23 nm
20
0
0,4
0,8
Pressure, GPa
1,2
1,6
Diameter of dislocation free iron particle is equal to 23 nm
M.I. Alymov, 1990
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
Density, %
100
90
80
Sintering
under pressure
Sintering
without pressure
70
Т2 < Т1
d2 < d 1
Sintering
temperature
Т1
d1
Equipment for the sintering under the pressure
Pressure
punch
yield of gas
bellows
thermocouple
padding
entrance of gas
heating element
sample
anvil
vessel
Pressure sintering of iron nanopowder
Density, %
100
380 MPa
280 MPa
90
90 MPa
80
0 MPa
70
60
400
500
600
700
Temperature, °С
800
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
Gas extrusion method
chamber
sample
die block
die
Nickel nanopowder green compact after hydrostatic pressing
Compacts of iron and nickel nanopowder after extrusion
Iron
10 cm
Nickel
TEM microstructure image of nickel
nanopowder compact after hot forging
Grain size near 70 nm
MECHANICAL PROPERTIES OF THE COMPACTS
Method
Hot isostatic
pressing
Material
Ni
Particle size,
mkm
Grain size,
mkm
в ,
MPa
,
%
6
25
440
36
0,06
1
545
7
40
55
350
41
0,04
1
460
1
0,06
0,1
700
15
Fe
Extrusion
Ni
Mechanical properties of
nanocrystalline and coarse-grained nickel
Nano-grained
Coarse-grained
0,2 , 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.
Ultimate strength , MPa
Ni
Fe
Cu
Relative elongation , %
Valiev R. 2001
Hardness of WC-8%Co hard alloy depends on
the size of WC-grain
Hardness HV, GPa
26
24
22
20
18
16
14
0
0,5
1,0
1,5
Size of WC-grain, mkm
2,0
Alymov M.I. a.o. Composites and Nanostructures. 2012.
SHS pressure sintering
4
3
1
4 - mold.
3 - insulating porous medium
(sand);
2
1 - tungsten spiral initiating the SHS reaction
2 - tablet from powders of the initial reactants
Sherbakov V.А.
Before SHS extrusion
Ignition system
Initial charge billets
Form of a matrix
The mold assembly
Guide caliber
Stolin A.M.
After SHS extrusion
Material after SHS
(press residue)
Extruded material
(finished product)
Stolin A.M.
Effectiveness for bulk nanopowder materials
Materials
Effectiveness
Hard 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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