SYNTHESIS AND CONSOLIDATION OF NANOPOWDERS: APPROACHES AND METHODS Cracow, 2014Michail Alymov ISMAN

Outline1. 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 nanomaterials1. 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, .509

METHODS FOR PROCESSING OF BULK NANOSTRUCTURED MATERIALS

MethodsTechnologiesMaterialsPowder metallurgyConsolidation of nanopowders:Pressing and sintering, Pressure sinteringMetals and alloys, ceramic, metal-ceramic, composites, polymersCrystallization from amorphous state Crystallization of amorphous alloys,Consolidation of amorphous powders with further crystallizationMetallic materialsable to bulk amorphisation.Severe plastic deformation Equal channel angular pressing, Torsion under high pressure, Multiple all-round forging.Metallic materialsNanostructurisation by precision heat treatment and thermomechanical treatmentHeat treatment. Thermomechanical treatmentMetallic materials

PressureTemperatureTimePowder Size of Ni particles = 70 nmBulk materialGrain size = 100 nm

Hydroxyapatite ceramics from nanopowdersPressure 3 GPa Sintering temperature 670Grain size 35-50 nm Microhardness 5,8 GPaFomin A.C., Barinov C.M., Ievlev V.. a.o. 2008. After pressingAfter 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, nm2000400Levitation-jet methodEEW4Plasma-chemicalChemical and metallurgical800SHSCalcium-hydride methodEvaporation-condensationAlymov 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, 19900 0,4 0,8 1,2 1,6 Pressure, GPa100

60

20Relative density, %23 nm26 nm28 nm60 nm120 nm1 mkm40 mkmDiameter 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 mechanisms1 - 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

Equipment for the sintering under the pressurethermocouplebellowsentrance of gassampleanvilyield of gasvesselheating elementpunchpaddingPressure

Pressure sintering of iron nanopowder 400 500 600 700 800 Temperature, 100Density, %380 MPa908070600 MPa90 MPa280 MPa.. , , 1997

Influence of the mode of deformation on sinteringHIP pressing in dies forging extrusion - ECAPHydrostatic component of pressureTangential component of pressure

Gas extrusion method

Compacts of iron and nickel nanopowder after extrusionIronNickel10 cmNickel nanopowder green compact after hydrostatic pressing

TEM microstructure image of nickel nanopowder compact after hot forgingGrain size near 70 nm

MECHANICAL PROPERTIES OF THE COMPACTS

MethodMaterialParticle size, mkmGrain size, mkm ,MPa, %Hot isostatic pressingNi625440360,0615457Fe4055350410,0414601ExtrusionNi0,060,170015

Mechanical properties of nanocrystalline and coarse-grained nickelThe crack growth resistance for nanocrystalline Ni is on 30% higher the crack growth resistance coarse grained Ni.

Nano-grainedCoarse-graineds0,2 , MPa53080sB , MPa625400d, % 2240, % 19,5-Kc , MPam1/282,351,7Toughness, J/cm263-66 198-203

NiValiev R. 2001FeCuUltimate strength , MPaRelative 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 Hardness HV, GPa14161820222426Alymov M.I. a.o. Composites and Nanostructures. 2012.

SHS pressure sintering Sherbakov V..1 - tungsten spiral initiating the SHS reaction2 - tablet from powders of the initial reactants3 - insulating porous medium (sand);4 - mold.

Before SHS extrusion Stolin A.M.

After SHS extrusion Stolin A.M.

Effectiveness for bulk nanopowder materials

MaterialsEffectivenessHard alloysIncrease of hardness by a factor of 5-7High strength steels and alloysIncrease of strength by a factor of 1,5-2

Ceramic materialsFormability as for titanium alloys Nanopowder materials with special propertiesMechanical, chemical, optical and other propertiesWear resistance coatingsIncrease of resistance by a factor of 170

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