Superhard nanocomposites


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Super Hard nano composites.
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Superhard nanocomposites

  1. 1. Superhard nanocomposites Submitted To: Dr. A. Subramania Associate Professor Centre for Nanoscience and Technology Pondicherry University Submitted By: Zaahir Salam
  2. 2. Vickers hardness test  The Vickers hardness test was developed in 1921 by Robert L. Smith and George E. Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials.  The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness.
  3. 3.  The basic principle, as with all common measures of hardness, is to observe the questioned material's ability to resist plastic deformation from a standard source. The Vickers test can be used for all metals and has one of the widest scales among hardness tests.  The unit of hardness given by the test is known as the Vickers Pyramid Number (HV) or Diamond Pyramid Hardness (DPH).  The hardness number can be converted into units of pascals. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not a pressure. To calculate Vickers hardness number using SI units one needs to convert the force applied from kilogram-force to newtons by multiplying by 9.806 65 (standard gravity ) and convert mm to m
  4. 4. Introduction  Today’s mechanical systems are in need of continuous improvements in enhancement of performance, durability and efficiency of the components.  So, Super hard nanocomposites have gained attention inorder to satisfy the needs.  Highly sophisticated surface related properties such as mechanical, chemical and tribological properties of super hard nanocomposites provide a best solution for the improved efficiency of today’s mechanical systems.
  5. 5. Classification On the basis of its hardness, nanocomposites are classified into 3 categories 1) Hard materials – Hardness greater than 20 Gpa 2) Super hard materials – Hardness greater than 40 Gpa 3) Ultra hard materials – Hardness greater than 80 GPa
  6. 6. Super Hard Nanocomposite Nanocomposites are materials that comprises of two different materials in a standard proportion, whose properties are better than the individual materials. Super hard nanocomposites (SHN) are those which posses a vicker’s hardness greater than 40 GPa. Such materials are widely applied as coatings over the mechanical devices.
  7. 7. Classification of Super Hard MaterialsMaterials Generally, Super hard materials can be broadly classified into 2 types  Intrinsically super hard materials Hardness arises due to the atomic arrangement itself. (E.g) Diamond, c- Boron Nitride.  Extrinsically super hard materials Hardness arises due to the external processes such as ion bombardment, production of nanocomposites. (E.g) nc-MN/a–Si3 N4 (M = Ti, W, V,etc.)
  8. 8. Intrinsically Super-Hard Materials Diamond and cubic BN generally exhibits this super hard capacity. This is due to the arrangement of the atoms present in the structure. For example, in diamond, the super hard property is due to the diamond cubic structure of the crystal. Hence, such materials found applications in mechanical systems, where high load and heat bearing capacity is inevitable.
  9. 9. Extrinsically Super- Hard Materials In extrinsically super hard materials, hardness is induced/generated in two ways 1. Ion bombardment 2. Formation of composites the
  10. 10. Ion bombardment The hardness of materials can be enhanced by bombarding the deposited film using high energy ions. The hardness enhancement is due to a complex effect involving o decrease of the crystallite size o densification of grain boundaries o formation of frenkel pairs and other point defects o built in biaxial compressive stress.
  11. 11. Hardness (vs) Compressive stress • First, very high enhancement of the hardness of TiN (up to 80GPa) and (TiAlV)N (up to 100 GPa) during deposition by means of unbalanced magnetron sputtering at negative substrate bias is found. • Later it was found that there is a correlation exist between the hardness enhancement and the biaxial compressive stress induced in the films.
  12. 12. Reason for Hardness • The highest hardness enhancement upon energetic ion bombardment is obtained in refractory hard ceramic coatings deposited at a relatively low temperature of about <300oC. • At a higher temperature, the hardness enhancement decreases and completely vanishes above 600–700 oC • Reason: The ion-induced effects anneal out during the film growth within the deeper regions that are not accessible to the ions with typical energy of a few 100 eV and corresponding projected ranges of <10 nm. • When the compressive (or tensile) stress is induced in a bulk specimen by bending it, such an enhancement (or decrease) doesn’t corresponds only to the amount of that stress. • Therefore, a compressive stress alone can never enhance the hardness to 60–100 Gpa , then ??????
  13. 13. Other Factors The hardness enhancement results from a complex synergistic effect of the – decrease of crystallite size – densification of grain boundaries – built in compressive stress – Formation of radiation damage (Frenkel pairs, etc.) upon energetic ion bombardment
  14. 14. Super Hard Composites  Depending on the crystallite size, the above said factors may hinder the dislocation activity  Dislocation activity is absent in the superhard thermally highly stable nanocomposites that consist of a few-nanometer small crystallites of a hard transition metal nitride (or carbide, boride,...) glued together by about one-monolayer-thin layer of nonmetallic, covalent nitride such as Si3N4, BN (or in the case of carbides by excess carbon, CNx, and others)
  15. 15. Properties • These coatings, when correctly prepared, posses an unusual combination of mechanical properties, such as • high hardness of 40 to 100 Gpa • high elastic recovery of 80% to 94%, • elastic strain limit of 10%, and • high tensile strength of 10 to 40 Gpa • Moreover, the nanostructure and the superhardness (measured at room temperature after each annealing step) remain stable up to 1100oC
  16. 16. Example • Superhard “Ti–Si–N” coatings were produced by means of plasma induced CVD (P CVD) using chlorides as a source of Ti and Si. • It is attributed the hardness enhancement to the precipitation of small Si3N4 particles within TiN nanocrystals. • The maximum hardness of 60–70 Gpa was probably due to ternary nc-TiN/a-Si3N4/a-TiSi2 nature of this coatings.
  17. 17. Hardness - Composite formation • In the majority of coatings deposited by PVD techniques at low pressure of the order of <10-3 mbar and negative substrate bias, there is a large biaxial compressive stress of 5 – 8 GPa due to the energetic ion bombardment during their deposition. • To check “if the measured hardness is not only enhanced by that bombardment” • When the coatings deposited were annealed to 600–800oC, the hardness increased to about 40 Gpa and the originally amorphous films showed nanocrystalline XRD patterns. • Thus, although the TiB2.2and TiN coatings deposited have a high hardness enhanced by energetic ion bombardment during their deposition , the hardness of the “Ti–B–N” coatings from the middle of the nitrogen range in is due predominantly to the formation of the nanocomposite structure • The hardness maximum at about 27% of nitrogen is less pronounced than usually found in our nanocomposites deposited by P CVD.
  18. 18. Evidence
  19. 19. Ion bombardment (vs)Composites Stability of the hardness upon annealing • The hardness that has been enhanced by energetic ion bombardment strongly decreases with annealing temperature to the ordinary bulk value upon annealing to 400–600oC • Superhard nanocomposites remains unchanged upon annealing up to 1100oC . • This softening upon annealing of the superhard coatings hardened by energetic ion bombardment is a general phenomena associated with the relaxation of ion-induced defects in the films that causes the hardness enhancement during deposition.
  20. 20. Stability of Hardness with annealing
  21. 21. Ion bombardment (vs)Composites Dependence of hardness with composition. • TiN1-xCx forms a solid solution and therefore the hardness follows the rule-of-mixtures • In the case of the so-called nanocomposites, consisting of a hard transition metal nitride and ductile metal, the maximum hardness is achieved with the pure nitride without that metal. • The superhard nanocomposites prepared according to our design principle show a maximum hardness at a percolation threshold.
  22. 22. Hardness (vs) Composition
  23. 23. Intrinsic vs Extrinsic Extrinsic materials are far better than the intrinsic materials.
  24. 24. Hardness (vs) Grain size • With a decrease in the grain size, the hardness of the materials increases. • Hall-petch relationship H(d) = H0 + Kd-1/2 • Dislocation movement, which determines the hardness and strength in bulk materials, has little effect when the grain size is less than approximately 10nm. • At this grain size, further reduction in grain size brings about a decrease in strength because of grain boundary sliding.
  25. 25. Hall petch relationship
  26. 26. Hardness Measurement • Good mechanical properties of a coating require •High hardness, •High toughness •low friction •High adhesion strength on substrate •Good load support capability and •Chemical and thermal stability, etc. • At present, nanoindentation is regarded as a good method in hardness determination. • In nanoindentation test, a diamond indenter is forced into the coating surface. The load and depth of penetration is recorded from which the hardness and other elastic properties are calculated.
  27. 27. Applications
  28. 28. Thank You