Recent advances in superhard nanocomposite coatings were presented. Nanocomposite coatings can be designed using various methods like combining two nanocrystalline phases or embedding nanocrystalline phases in an amorphous matrix to improve hardness and toughness. Coatings are synthesized using methods like chemical vapor deposition or magnetron sputtering. Properties are evaluated through nanoindentation, scratch adhesion testing, and measuring fracture toughness. Designing coatings with optimized parameters can provide both high hardness and toughness making nanocomposite coatings suitable for industrial applications.

1. Recent advances of superhard nanocomposite
coatings
PRESENTED BY
D. RATHIRAM NAIK, P. VIJAYA DURGA
15MT60R35, 15MT60R46
IIT KHARAGPUR
Sam Zhang, Deen Sun, Yongqing Fu, Hejun Du

2. Contents
Introduction
Classification of coatings on the basis of hardness
Design methodology for nanocomposite coatings
Possible design methods
• Results
Synthesis methods
• Chemical Vapor Deposition (CVD)
• Magnetron sputtering
Evaluation of mechanical properties
Conclusion
References

3. Why coatings?
• To protect from physical and chemical
degradation.
• Wear-, corrosion-, and fatigue
resistance
• To improve the service life of cutting
tools
• To enhance the overall performance
• To improve the productivity

4. Introduction
•Highly sophisticated surface related properties obtained by advanced
nanostructured coatings :
 optical
 magnetic
Electronic
Mechanical
 chemical and tribological properties
•Industries prefer coatings because of their special properties listed above due to
size effect
•Properties depends on material selection, deposition methods and process
parameters

5. Applications
 Automotive body parts
Jewellery
Mirrors
Medical field
Mechanical fields
Oxidation resistance
• On cutting tools
• Chemical factories

7. Design methodology for nanocomposite coating
• Reduction in grain size (<10nm) leads to decrease in strength because of grain
boundary sliding
• Softening by grain boundary sliding attributes to large amount of defects in
grain boundaries
To increase hardness and toughness
• Requires hindering of grain boundary sliding by increasing the complexity and
strength of grain boundaries
Multiphase structures gives complexity at grain boundaries
By termination of Nano cracks
• With decreasing the grain size according to “Hall-Petch” relationship

8. Hardness as a function of grain size

9. Possible design methods
• A combination of two or more nanocrystalline
phases:
Example: TiN-TiB2, Ti-B-N
Results in increasing coating hardness
• Segregation of nanocrystalline phases to grain
boundaries
Advantage:
o increase in hardness and elastic modulus
Disadvantage:
o Lack of toughness

10. Design methodology
•Hard nanocrystalline phases within a metal matrix:
TiN in Ni
ZrN in Ni
Zr-Y-N, ZrN in Cu
CrN in Cu
•Resulted 35 – 60 Gpa hardness
•Contribution to hardness:
 Dislocation mechanism
 Grain boundary mechanism
•Metal Matrix improves toughness

11. Design methodology (Contd..)
•Disadvantage:
• Poor toughness
• Lack of thermal stability
•To improve thermal stability
 Addition of high thermal stability element
Example: Yittrium
Modify the interface complexity by ternary system
Embed nanocrystalline phases in an amorphous phase matrix

12. Enhancement of toughness along with hardness
• Embed nanocrystalline phases in an amorphous phase matrix
•Amorphous matrix
•Possess high structural flexibility to accommodate
coherent strains
•Helps to deflect and terminate nanocracks
•Grain boundary sliding
•Improved coating toughness
•Matrix with high hardness and elastic modulus
• Eg. DLC, carbon nitride

13. Continued
•Strength phases: Nano-sized refractory nitride
• Should be random orientation
oMinimizes incoherent strains
oEasy slide in amorphous matrix to release strain and obtains high toughness
• Eg. TiN, Si3N4, AlN, BN
•The size, volume percentage and distribution of the nanocrystals need to be
optimized
• The distance between two Nano crystals should be within a few nanometres
• Too large distance cause crack in matrix
• Too close to each other will cause interaction of planes

14. Results
Nano crystalline
phase
Matrix Hardness
(GPa)
TiC DLC 32
TiN Si3N4 50 - 70
TiCrCN DLC 40
TiN, TiS2 Si3N4 105 GPa
These Coatings are having thermal stability also

15. Synthesis methods
CHEMICAL
VAPOR
DEPOSITION
MAGNETRON
SPUTTERING

16. Chemical Vapor Deposition
1. Transport of reactants deposition
chamber
2. Diffusion of reactants towards substrate
3. Adsorption of reactants on the substrate
4. Surface reaction
5. Desorption of by-products away from
substrate
6. Transport of by-products by diffusion
7. Transport of by-products away from
chamber

17. CVD Continued
•Advantages compared sputtering:
High deposition rates
Uniform deposition for complicated geometries
•Disadvantages:
Low deposition temperature difficult to maintain
oSubstrate distortion
•Main problem:
• Precursor gases(TiCl4, SiCl4) creates problem due to their corrosive nature
• Chloride induces interface corrosion

18. Magnetron Sputtering
Basic Sputtering process:
atoms are ejected from the surface of a
material when that surface is stuck by
sufficiency energetic particles.
1. Ions are generated and
directed at a target.
2. The ions sputter targets
atoms.
3. The ejected atoms are
transported to the
substrate.
4. Atoms condense and form
a thin film.

19. Continued
Limitation of basic sputtering process
• Low deposition rates
•Low ionisation efficiencies in the plasma
•High substrate heating
Above limitations are overcome by magnetron sputtering

20. Magnetron Sputtering(MS)
Magnets are used to increase the
percentage of electrons that take part in
ionization events, increase probability of
electrons striking
Another reasons to use magnets:
◦ Lower voltage needed to strike
plasma.
◦ Controls uniformity.
◦ Reduce wafer heating from electron
bombardment.
◦ Increased deposition rate

21. Continued
• Trapping the electrons increases the
probability of an ionising electron atom
collision occurring.
• The increased ionisation results in a
dense plasma
•This leads to increased ion bombardment
of the target, giving higher sputtering
rates
•Therefore, higher deposition rates at the
substrate.

22. Continued
MS can operate at low temperatures to deposit films with controlled texture and
crystallite size
Process parameters affecting the grain size of coatings:
• Substrate temperature
• Substrate ion Current density
• Bias voltage
• Partial pressure of reactive gas (e.g. Nitrogen for nitrides)
• Post annealing temperature

23. Evaluation of mechanical properties
 Nanoindentation: Vickers hardness test. A diamond indenter is forced into the
coating surface
Hardness of coating depends:
• Load
• Evaluation method
• Depth of penetration
• Residual stress

24. Fracture toughness
 The ability of a material to resist the growth of pre-existing crack
Evaluation method-1: ultra- low load indentation
• If no crack is forming then coating is having good toughness
Evaluation method -2: based on the energy released in through – thickness
cracking
• Area under the indentation profile

25. Continued
Fracture process follows three steps
• Stage-1:
ofirst ring like crack form around the
indenter
• Stage -2:
o delamination and buckling at
coating – substrate interface
• Stage -3:
oSecond ring like crack due to high
stress

26. Fracture toughness
 Area under the indentation profile
 OACD is loading and DE is unloading
 Energy difference is ABC
 Strain energy is released to create crack
 Fracture toughness given by

27. Adhesion of coating
 Big concern for industrial coatings
Adhesion of coating gives good load
bearing capacity
To improve adhesion : Add a bonding
layer in between
Evaluation method: Scratch adhesion
test

28. Conclusions
Various deposition techniques have been used to prepare nanocompositie
Advantageous methods magnetron sputtering and CVD
Attention is paid to increase hardness , toughness and thermal stability
Optimum design of parameters gives good hardness and toughness
Superhard nanocompositie coatings needs vigorous theoretical and
experimental verification

29. References
[1] Sam Zhang, Deen Sun, Yongqing Fu, Hejun Du, a riview on recent advances of nano composite coatins,
Surface and coating Technology 167 (2003), 113-119
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