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TiN-C60 - Thesis Presentation (Yan Valsky)


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Yan Valsky - TiN-C60 - Thesis Presentation

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TiN-C60 - Thesis Presentation (Yan Valsky)

  1. 1. A Thesis submitted toward the degree of Master of Science in Tel Aviv University by Yan Valsky Supervisors: Engineering Faculty - Dr. Vladimir Zhitomirsky Engineering Faculty - Prof. Reuven L. Boxman Exact Sciences Faculty - Prof. Gil Markovich Novel Wear Resistant TiN-C 60  Coatings Deposited Using Combination of Filtered Vacuum Arc and Effusion Cell Techniques Aug 21, 2010 TAU - EDPL Tel-Aviv University Raymond and Beverly Sackler Faculty of Exact Sciences School of Chemistry, Materials Science Program
  2. 2. Outline <ul><li>Introduction (theory & literature) </li></ul><ul><ul><li>TiN coating properties, improvement TiN properties </li></ul></ul><ul><ul><li>Fullerenes: WS 2 (shortly), C 60 (tribological properties) </li></ul></ul><ul><ul><li>Deposition processes (Vacuum arc, Effusion cell) </li></ul></ul><ul><li>Project goals </li></ul><ul><li>Experimental apparatus and procedure </li></ul><ul><li>Results and discussion </li></ul><ul><li>Summary and conclusions </li></ul><ul><li>Open questions and recommendations </li></ul>Aug 21, 2010 TAU - EDPL
  3. 3. <ul><li>``The cost of friction in the US alone, in terms of wear and energy consumption is estimated at $120b annually - approximately 1%-1.5% of GDP`` </li></ul><ul><li>Argonne National Laboratory, US Department of Energy, 1999 </li></ul>Aug 21, 2010 TAU - EDPL
  4. 4. TiN (titanium nitride) coating Aug 21, 2010 TAU - EDPL
  5. 5. TiN properties <ul><li>Color – gold (depends on stoichiometry) </li></ul><ul><li>B1 crystal structure </li></ul><ul><li>High (111) orientation, single δ -TiN x </li></ul><ul><li>Hardness – 2000-3000 kg/mm² (19-29 GPa) </li></ul><ul><li>Melting temperature – 2950°C </li></ul><ul><li>Coefficient of friction ~0.13-0.17 </li></ul><ul><li>Oxidizes at 1200°C </li></ul><ul><li>Adhesion – 20-90 N </li></ul><ul><li>Mechanical properties depends on substrate material, substrate temperature, bias voltage, nitrogen pressure, film thickness </li></ul>Aug 21, 2010 TAU - EDPL
  6. 6. Improving TiN based coatings <ul><li>Multi component - (Ti,Al)N, (Ti,Nb)N, (Ti,Zr)N, (Ti,B)N, (Ti,Cr)N, (Ti,Cr,B)N, (Ti,Si,B)N, (Ti,Al,Si,B)N, (Ti,B,C)N, (Ti,Hf)N </li></ul><ul><li>Multi-layer – Ti/TiN, TiN/NbN, TiN/ZrN, TiN/VN, TiN/CrTiN/VNbN, TiN/TaN, TiN/MoN </li></ul><ul><li>Superlattice - TiN/Nb , TiN/TaN </li></ul><ul><li>Nanocomposite - nc-TiN/a-Si 3 N, nc-(TiC/TiN)/a-B 4 C, nc-(Ti,Al,N,C)/a-C, nc-TiAlN/a-Si 3 N 4 </li></ul><ul><li>Embedded fullerenes – TiN-MoS 2 </li></ul>Aug 21, 2010 TAU - EDPL
  7. 7. TiN with embedded fullerenes <ul><li>MoS 2 fullerenes – exhibit low COF (0.01) and extended lifetime in vacuum </li></ul><ul><li>In coatings - expected to behave like nano-ball bearings and upon mechanical stress they would slowly exfoliate or mechanically deform </li></ul><ul><li>Problem - tribological properties remain poor in the presence of humidity or oxygen </li></ul><ul><li>Piazzoni - successfully incorporated MoS 2 in TiN matrix by co-deposition (TiN deposited by VAD). Improves coating adhesion, the process needs to be optimized [ Appl. Phys. A 90, 101–104 (2008) ] </li></ul>Aug 21, 2010 TAU - EDPL
  8. 8. Cont’ <ul><li>(Left) Cross section TEM micrograph of a MoS 2 /TiN nanocomposite film produced using the multilayer deposition mode. 10–50 nm size IF-MoS 2 are dispersed in the TiN matrix. The silicon substrate and TiN matrix can be clearly recognized. (Right) higher magnification view of the same region showing the structure of MoS 2 nanoparticles </li></ul>Aug 21, 2010 TAU - EDPL
  9. 9. Fullerenes – C 60 <ul><li>Hollow carbon cage of ~1 nm in diameter </li></ul><ul><li>Stable in air </li></ul><ul><li>Film is stable under hydrostatic compression to at least 20 GPa </li></ul><ul><li>Sublimes readily at temperatures above about 450 o C </li></ul><ul><li>Stable up to KeV ion irradiation </li></ul><ul><li>High robustness </li></ul><ul><li>Can be exploited as molecular shock absorbers and can carry heavy loads </li></ul><ul><li>May be present as loose wear particles which may roll in a sliding contact resulting in low friction and wear </li></ul>Aug 21, 2010 TUA - EDPL
  10. 10. C 60 as solid lubricant <ul><li>Bulk film – high COF ~0.75-0.80 </li></ul><ul><li>Monolayer between graphite substrates – COF ~ 0.15 (C 60 rolls) </li></ul><ul><li>Additives to mineral oils and greases – COF ~ 20% improvement </li></ul><ul><li>Examination of the above reports indicates that the effectiveness of C 60 fullerenes as a solid lubricant depends on the circumstances. No general rule is currently evident. </li></ul>Aug 21, 2010 TUA - EDPL
  11. 11. C 60 identification <ul><li>Raman spectroscopy XPS </li></ul><ul><li>SIMS-TOF </li></ul>Aug 21, 2010 TAU - EDPL
  12. 12. Background summary <ul><li>Vacuum arc deposited TiN coating was used as the matrix of composite materials consisting of a hard matrix with embedded lubricating fullerenes </li></ul><ul><li>C 60 fullerenes may be used as solid lubricant embedded in various matrix </li></ul><ul><li>No data is available on TiN with embedded C 60 fullerenes. </li></ul><ul><li>OPEN QUESTIONS </li></ul><ul><li>Can nano-structured coatings could be synthesized, having a hard TiN ceramic matrix in which C 60 molecules are embedded? </li></ul><ul><li>Will these C 60 molecules would be dislodged during wear and form a self-lubricating tribo-film? </li></ul>Aug 21, 2010 TAU - EDPL
  13. 13. Project goals <ul><li>To synthesize nano-composite TiN-C 60 coatings </li></ul><ul><li>To determine their wear and friction characteristics </li></ul><ul><li>In the course of this research: </li></ul><ul><ul><li>A deposition process using a combination of FVAD apparatus for TiN hard coating matrix, and an effusion cell for C 60 fullerene deposition was developed </li></ul></ul><ul><ul><li>The composition, structure, and tribological properties of the films were determined as functions of the deposition process parameters </li></ul></ul>Aug 21, 2010 TAU - EDPL
  14. 14. TiN deposition - Vacuum Arc <ul><li>Physical vapor deposition (PVD) process/technique </li></ul><ul><li>Cathodic vacuum arc </li></ul><ul><li>High-current, low-voltage electrical discharge which produces plasma consisting of vaporized and ionized electrode material </li></ul><ul><li>Plasma flow generated from the cathode spots is transported to the substrate </li></ul>Aug 21, 2010 TAU - EDPL Cathode spots on cathode surface
  15. 15. C 60 deposition – Effusion cell <ul><li>Based on the principle of molecular effusion initially demonstrated by Knudsen (1900) </li></ul><ul><li>A sample material is held in a source capsule, with a small hole in one of its walls </li></ul><ul><li>The sample is assumed to maintain its equilibrium vapor pressure inside the capsule, while the outside of the capsule is in vacuum </li></ul><ul><li>The material to be deposited is heated to provide a suitable vapor pressure in an isothermal enclosure </li></ul><ul><li>Vapor molecules leak out of the capsule into the vacuum </li></ul>Aug 21, 2010 TAU - EDPL
  16. 16. Cont’ <ul><li>Effusion rate - </li></ul>Aug 21, 2010 TAU - EDPL 1 st ceramic tube Flat base Thermocouple gauge connection Stem Ceramic barrier 2 nd ceramic tube Stainless steel tube Titanium tube Flange PID (+) (-) DC power Supply
  17. 17. Experimental apparatus for deposition TiN-C 60 Aug 21, 2010 TAU - EDPL Effusion Cell
  18. 18. Cont’ Aug 21, 2010 TAU - EDPL Ti cathode
  19. 19. Coating characterization <ul><li>Thickness </li></ul><ul><li>Color and appearance </li></ul><ul><li>SEM, TEM </li></ul><ul><li>XRD </li></ul><ul><li>EDX </li></ul><ul><li>XPS </li></ul>Aug 21, 2010 TAU - EDPL <ul><li>SIMS-TOF </li></ul><ul><li>RAMAN spectroscopy </li></ul><ul><li>Adhesion (L C ) </li></ul><ul><li>COF </li></ul><ul><li>Micro-hardness </li></ul>
  20. 20. Results - Pure TiN Coatings <ul><li>Appearance - nitrogen pressure and substrate temperature </li></ul><ul><li>Adhesion (tape test) </li></ul>Aug 21, 2010 TAU - EDPL Nitrogen pressure, mTorr Substrate Temperature, o C 100 ± 10 150 ± 10 200 ± 10 250 ± 10 1 Bright yellow Bright yellow Bright yellow Bright yellow 2 Yellow Yellow Yellow 3 Dark yellow Dark yellow 4 Bright Brown Nitrogen pressure, mTorr Substrate Temperature, o C 100 ± 10 150 ± 10 200 ± 10 250 ± 10 1 good good good Good 2 good good good Good 3 good good 4 good
  21. 21. Cont’ <ul><li>Crystalline structure, Elemental composition (EDX) </li></ul><ul><li>Deposition rate - 100±5 nm/min </li></ul>Aug 21, 2010 TAU - EDPL Ti N
  22. 22. Results - Pure C 60 film <ul><li>Distance </li></ul><ul><li>Radius circle 3 cm away - 5 mm </li></ul><ul><li>Radius circle 8 cm away - 12 mm </li></ul><ul><li>Deposition rate </li></ul><ul><li>Calculated - 24±4 nm/min </li></ul><ul><li>Measured (3 cm) - 27±1 nm/min; (8 cm) - 0.24±0.02 nm/min </li></ul>Aug 21, 2010 TAU - EDPL
  23. 23. Cont’ <ul><li>Raman spectroscopy </li></ul><ul><li>XPS </li></ul>Aug 21, 2010 TAU - EDPL
  24. 24. Procedure for TiN-C 60 deposition <ul><li>Deposited TiN-C 60 coatings </li></ul>Aug 21, 2010 TAU - EDPL TiN matrix TiN layer C 60 layer Si Si C 60 fullerenes Coating composition TiN, first layer (nm) C 60 (nm) TiN (nm) No. of layers Layered 50-200 5-40 50-500 1-8 Embedded 200 0.3-0.7 8-17 10-36
  25. 25. TiN-C 60 coating deposition <ul><li>Color - The color varied from yellow to purple or brown. Among the studied samples, no correlation between the deposition parameters and coating color was found </li></ul><ul><li>Adhesion - Most of layered type TiN-C 60 coatings showed bad tape test adhesion, and are listed as “peeled”. No correlation was found between coating thickness, layer thickness or mol.% C 60 and the adhesion. Embedded type TiN-C 60 coatings showed good tape test adhesion </li></ul>Aug 21, 2010 TAU - EDPL
  26. 26. Cont’ <ul><li>HR-SEM, TEM – delaminated layers are seen </li></ul>Aug 21, 2010 TAU - EDPL
  27. 27. Cont’ <ul><li>Crystalline structure - The XRD detected only the TiN cubic phase in the TiN-C 60 coatings; no crystalline C 60 was observed </li></ul>Aug 21, 2010 TAU - EDPL
  28. 28. Cont’ <ul><li>Raman spectroscopy - The Raman scattering spectrum of C 60 fullerenes has unique vibrational peaks at 1425 cm ‑1 , 1469 cm -1 and 1573 cm -1 </li></ul><ul><li>The C 60 peaks were only observed in one sample (mol.9% C 60 ) </li></ul><ul><li>Signs of polymerizations or structural destruction were not observed </li></ul>Aug 21, 2010 TAU - EDPL
  29. 29. Cont’ <ul><li>XPS studies - representative sample with 1.6 mol.% of embedded C 60 </li></ul><ul><li>High oxygen concentration (~40%) was also found in the sample </li></ul>Aug 21, 2010 TAU - EDPL
  30. 30. Cont’ <ul><li>TOF-SIMS - representative sample with mol.1.8% of C 60 embedded. </li></ul><ul><li>Some C 12 fragments were detected, which may indicate C 60 decomposition process during interaction with the sputter ion gun in the SIMS apparatus </li></ul>Aug 21, 2010 TAU - EDPL C 1 C 2 C 5 C 6 C 9 C 10 C 11 C 12
  31. 31. Mechanical properties <ul><li>Coating fracture at indentation </li></ul><ul><li>The crack around the indentation was </li></ul><ul><li>graded using 0-6 grading scale </li></ul>Aug 21, 2010 TAU - EDPL <ul><li>Critical load </li></ul><ul><li>Critical load defined as the indentation load at which a concentric crack in the coating around the indentation was observed </li></ul>
  32. 32. Cont’ <ul><li>Hardness (Vickers) </li></ul>Aug 21, 2010 TAU - EDPL <ul><li>Coefficient of friction </li></ul>
  33. 33. Cont’ Aug 21, 2010 TAU - EDPL <ul><li>Wear rate </li></ul>
  34. 34. Discussion <ul><li>Substrate temperature of 100 o C during TiN-C 60 deposition: </li></ul><ul><ul><li>Good adhesion of the coatings </li></ul></ul><ul><ul><li>Preventing C 60 “bouncing-back” due to thermal energy </li></ul></ul><ul><li>It was impossible to simultaneously deposit TiN and C 60 with a reasonable concentration with the FVAD and EC sources because of the large difference in their deposition rates (100 nm/min for TiN, and 0.3 nm/min for C 60 ) </li></ul>Aug 21, 2010 TAU - EDPL
  35. 35. Cont’ <ul><li>The impact of energetic Ti ions could destroy the C 60 spherical structure. However, XPS and Raman spectra showed that the C 60 at least partially survived </li></ul><ul><li>The origin of the oxygen was not determined, but possibly fullerenes were oxidized when the system was opened </li></ul><ul><li>The amount of C 60 fullerenes within the coatings was not quantitatively measured. The molecular percentage of C 60 was based only on calculations based on the measured individual deposition rates </li></ul>Aug 21, 2010 TAU - EDPL
  36. 36. Cont’ <ul><li>Adhesion at micro indentation of layered coatings failed between the layers. The failure was probably caused by stress forces in the TiN coating </li></ul><ul><li>In contrast, embedded coatings adhered well most probably due to continuous TiN matrix connection </li></ul><ul><li>All but one embedded sample showed lower (better) indentation adhesion than pure TiN coatings. Microhardness testing showed that the coating sample was softer, ~950 HV, than TiN, 1300 HV. This could explain the indentation behavior – the indenter penetrated the TiN-C 60 coating without brittle fracture or coating detachment and thus the embedded C 60 increased the L C </li></ul>Aug 21, 2010 TAU - EDPL
  37. 37. Cont’ <ul><li>Wear scratch tests showed no obvious correlation between the C 60 fraction, in the range of 0.4-2.4 mol% C 60 , and the COF </li></ul><ul><li>The scatter in COF results may be attributed to surface roughness difference between the samples - thus after 12 min of wear, the scatter significantly decreased </li></ul><ul><li>The hypothesis that C 60 fullerenes would create a self-lubricating tribo-film which reduces friction was not verified </li></ul>Aug 21, 2010 TAU - EDPL
  38. 38. Conclusions <ul><li>TiN-C 60 coatings were successfully deposited using a combination of FVAD for TiN and EC for C 60 deposition processes </li></ul><ul><li>C 60 fullerenes were present in at least some of the coatings as proven by Raman spectroscopy, XPS and SIMS </li></ul><ul><li>Generally it was found that the wear properties of TiN-C 60 coatings relative to TiN was not improved by incorporating C 60 into the TiN matrix, and adhesion was decreased </li></ul><ul><li>Possibly, further studies will reveal more favorable conditions for TiN-C 60 deposition from the point of view of mechanical properties </li></ul>Aug 21, 2010 TAU - EDPL
  39. 39. Open questions <ul><li>Why fullerenes were detected in some samples, but not in others? </li></ul><ul><li>Is it was possible to obtain higher C 60 deposition rate and operate in a simultaneous deposition mode? How would this affect coating properties? </li></ul><ul><li>The estimates of mol.% C 60 in the TiN-C 60 were based on the calculated values based on the individual C 60 and TiN deposition rates. How well does this estimate correlate with the actual C 60 concentration? </li></ul><ul><li>Did the oxygen affect the coating properties? </li></ul>Aug 21, 2010 TAU - EDPL
  40. 40. Recommendations <ul><li>Using an effusion cell with higher fullerene deposition rate, TiN-C 60 coatings with higher C 60 percentage fraction should be deposited and studied </li></ul><ul><li>Using the combined FVAD and EC techniques developed, other composite coatings may be studied, e.g. other fullerenes in a TiN matrix or in other well known and used hard coatings, e.g. TiAlN </li></ul>Aug 21, 2010 TAU - EDPL
  41. 41. <ul><li>Question are guaranteed in life; </li></ul><ul><li>Answers aren’t </li></ul>Aug 21, 2010 TAU - EDPL
  42. 42. <ul><li>Appendix </li></ul>Aug 21, 2010 TAU - EDPL
  43. 43. C 60 molecular concentration <ul><li>A c is the area of the coating, X TiN is TiN layer thickness (t d × R d ), N A is the Avogadro number, ρ is the coating density, M is the TiN molar mass </li></ul>Aug 21, 2010 TAU - EDPL A c is the area of the coating, X C60 is C 60 layer thickness (t d × R d ), V C60 is the volume of C 60 molecule X is the ratio between the C 60 layer thickness and the TiN layer thickness
  44. 44. Arc stability <ul><li>Spatial distribution and centering of the plasma beam (torus coil current, Helmholtz coil currents, beam steering coil currents) </li></ul>Aug 21, 2010 TAU - EDPL Magnetic Coil Chosen coil current, A Converting const, mT/A Magnetic field, mT Cathode coil 10 0.2 -2 Toroidal coils 2.3 6 13.8 Helmholtz 1 coil 1.5 3.6 5.4 Helmholtz 2 coil 1.5 3.6 5.4 Steering beam X coil 1 4 4 Steering beam Y coil 1 4 4
  45. 45. VAD main problems <ul><li>Macroparticles; Solution – filter (lowers dep.rate) </li></ul><ul><li>Cathode spots “run away” from surface causing arc instability and non uniform erosion; Solution – control the spot motion (lowers efficiently) </li></ul><ul><li>How? – Magnet field (B): </li></ul><ul><li>Cathode spots move in the – JxB direction </li></ul><ul><li>Acute angle (a) rule </li></ul>Aug 21, 2010 Cathode Filter TAU - EDPL