Cracow 2014 SYNTHESIS AND CONSOLIDATION OF NANOPOWDERS APPROACHES

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 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 Chemical and metallurgical Evaporationcondensation EEW Levitation-jet 4 0 0 method 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 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 Т 2 < Т 1 d 2 < d 1 Sintering temperature Т 1 d 1

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 , 6 25 440 36 0, 06 1 545 7 40 55 350 41 0, 04 1 460 1 0, 06 0, 1 700 15 MPa , % Fe Extrusion Ni

Mechanical properties of nanocrystalline and coarse-grained nickel Nano-grained Coarse-grained s 0, 2 , MPa 530 80 s. B , MPa 625 400 d, % 22 40 ψ, % 19, 5 - Kc , MPa∙m 1/2 82, 3 51, 7 Toughness, J/cm 2 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 Dziękuję za uwagę