SYNTHESIS AND CONSOLIDATION OF NANOPOWDERS: APPROACHES AND METHODS

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

2. 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.

3. 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

4. METHODS FOR PROCESSING OF BULK NANOSTRUCTURED MATERIALS

5. Bulk material Powder Pressure Temperature Time Size of Ni particles = 70 nm Grain size =100 nm

6. Hydroxyapatite ceramics from nanopowders After pressing After sintering Grain size 35-50 nmMicrohardness 5,8 GPa Pressure 3 GPaSintering temperature 670°С Fomin A.C., Barinov C.M., IevlevV.М. a.o. 2008.

7. 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-gelmethod - hydrothermal synthesis and others

8. 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.

9. The ratio between the average particle size and performance of methods Capacity, g/h 800 SHS 400 Calcium-hydride method Plasma-chemical 200 EEW Levitation-jet method Chemical and metallurgical 4 0 0 200400 Size of particles, nm Evaporation-condensation Alymov M.I. Composites and Nanostructures, 2012, v.3.

10. METHODS forthe NANOPOWDERS CONSOLIDATION Uniaxial pressing: static, dynamic, vibration Isostatic pressing Extrusion Sintering under pressure Spark plasma sintering Sock wave pressing Severe plastic deformation

11. 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.

12. Cold pressing - uniaxial (static, dynamic, vibrational), - multiaxial (hydrostatic, gasostatic), - severe plastic deformation, - cold rolling.

13. Influence of average iron particle diameter on the density of compacts 100 60 20 40 mkm 1 mkm 120 nm 60 nm Relative density, % 28 nm 26 nm 23 nm 0 0,4 0,8 1,2 1,6 Pressure, GPa Diameter of dislocation free iron particle is equal to 23 nm M.I. Alymov, 1990

14. 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.

15. Consolidation process of nanopowders is strongly affected by: - particle size distribution, - concentration of impurities, - surface conditions, - particle shape, - pressing technique.

16. 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.

17. Sintering of gold nanoparticles

18. 100 90 Density, % Sintering under pressure Sintering without pressure 80 70 Т1 Т2< Т1 Sintering temperature d1 d2< d1 Influence of pressure on sintering

19. Equipmentfor the sintering under the pressure Pressure punch yield of gas bellows thermocouple padding entrance of gas heating element sample anvil vessel

20. Pressure sintering of iron nanopowder 100 380 MPa 280 MPa 90 90 MPa Density, % 80 0 MPa 70 60 400 500 600 700 800 Temperature, °С М.И. Алымов, ФХОМ, 1997

21. Influence of the mode of deformation on sintering HIP – pressing in dies – forging – extrusion - ECAP Hydrostatic component of pressure Tangential component of pressure

22. gas chamber sample die die block Gas extrusion method

23. Nickel nanopowder green compact after hydrostatic pressing Compacts of iron and nickel nanopowder after extrusion Iron 10 cm Nickel

24. TEM microstructure image of nickel nanopowder compact after hot forging Grain size near 70 nm

25. MECHANICAL PROPERTIES OF THE COMPACTS

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

27. Ni Fe Ultimate strength, MPa Cu Relative elongation, % Valiev R. 2001

28. Hardness of WC-8%Co hard alloydepends on the size of WC-grain 26 24 22 20 Hardness HV, GPa 18 16 14 0 0,5 1,0 1,5 2,0 Size of WC-grain, mkm AlymovM.I. a.o.Composites and Nanostructures. 2012.

29. 4 3 2 1 SHS pressure sintering 4 - mold. 3 - insulating porous medium (sand); 1 - tungsten spiral initiating the SHS reaction SherbakovV.А. 2 - tablet from powders of the initial reactants

30. Ignition system Initial charge billets Form of a matrix The mold assembly Guide caliber Before SHS extrusion Stolin A.M.

31. Material after SHS (press residue) Extruded material (finished product) After SHS extrusion Stolin A.M.

32. Effectivenessfor bulk nanopowder materials

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