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Novel Double-layered Titanium Boride Coatings on Titanium: Kinetics of Boron Diffusion and Coating Morphologies Nishant Tikekar, K.S. Ravi Chandran and Tony Sanders* Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT * Ortho Development Corporation, Draper, UT

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  1. Novel Double-layered Titanium Boride Coatings on Titanium:Kinetics of Boron Diffusion and Coating Morphologies Nishant Tikekar, K.S. Ravi Chandran and Tony Sanders* Department of Metallurgical Engineering, University of Utah, Salt Lake City, UT * Ortho Development Corporation, Draper, UT TMS 2005 - 134th Annual Meeting and Exhibition Supported by: Utah State Center of Excellence Ortho Development Corporation

  2. Outline • Overview • Motivation for research • Experimental: • Boron diffusion treatment • Results: • Temperature and time effects • Double layer coating morphology • Layer growth kinetics • Conclusions

  3. Problems with titanium surfaces • Titanium is rarely used in wear resistant applications • Problems: • High friction • Galling and gouging • Poor contact deformation resistance • Contact fatigue crack formation and damage • A strong and integral coating is needed

  4. Surface modification processes • Laser and Electron Beam based techniques • Ion Implantation • Physical Vapor Deposition • Chemical Vapor Deposition • Diffusion treatments – Preferred • Method analogous to carburizing of steel is advantageous Titanium boride (TiB) on titanium?

  5. What is TiB and TiB2? • Hard titanium compounds Ti-B phase diagram Crystal structure of TiB and TiB2 • TiB at 18-18.5%B • Ti3B4 at 22.4%B • TiB2 at 30.1-31.1%B

  6. Research Focus • In-situ creation of Titanium Boride (TiB) whiskers in Ti and Titanium Diboride (TiB2) • High elastic modulus (E of TiB = 370 GPa) • High Vickers hardness of TiB (Hv ~ 1800@1kg load) • High Vickers hardness of TiB2 (Hv ~ 3200@1kg load) • “Clean” Ti-TiB interface • Develop an “integral” boride coating

  7. Experimental • Polished Ti-6Al-4V samples • Ball-milled powders • Boron source, activator and a transport medium • Diffusion studies • Parameters studied: • Treatment temperatures: 950-1200°C • Time at different temperatures: 3-24 hours

  8. X-Ray analysis TiB2 layer TiB whisker As-treated surface After removing 20mm

  9. 10mm Temperature effects 950ºC for 24 hours 1050ºC for 24 hours 1200ºC for 24 hours 1100ºC for 24 hours

  10. 10mm Effect of time at 1050ºC 3 hours 6 hours 12 hours 24 hours

  11. TiB2 thickness variation • At a fixed temperature, TiB2 thickness increases by a maximum of 10mm from 3 to 24 hours • The thickness variation depends on the treatment temperature

  12. TiB2 thickness variation Monolithic thickness (mm) Time (h)

  13. TiB2 thickness variation Monolithic thickness cubed (mm3) Time (h)

  14. TiB thickness variation • At a fixed temperature, TiB thickness increases significantly from 3 to 24 hours • The thickness variation depends on the treatment temperature and time

  15. TiB thickness variation TiB thickness (mm) Time (h)

  16. Parabolic diffusion? TiB thickness variation with temperature and time ? TiB thickness squared (mm2) ? Time (h)

  17. Double layer thickness variation • At a fixed temperature, total (TiB+TiB2) thickness increases significantly from 3 to 24 hours • Total thickness increases with increasing combination of time and temperature

  18. Double layer thickness variation Total coating thickness (mm) Time (h)

  19. Kinetics of Double Layer Total thickness variation with temperature and time Total thickness squared (mm2) Time (h) • Parabolic growth behavior: Diffusion-controlled boride layer growth

  20. Thin TiB2 layer Increasing TiB2 layer Slowly increasing TiB2 layer Increasing TiB whiskers Thicker TiB whiskers Small TiB whiskers TiB whiskers Powder pack Powder pack Powder pack Powder pack Alloy matrix Alloy matrix Alloy matrix Alloy matrix Process Model *Illustrations not to scale

  21. Some Interesting observations • TiB2 thickness increases with T for a given time • Lower T, Shorter t, thinner TiB whiskers • Inconsistent trends at 1050 and 1100ºC: Shorter times: TiB layer thickness at 1050ºC > than at 1100ºC Longer times: TiB layer thickness at 1050ºC < than at 1100ºC • Beta transus ~1010ºC: • Variability introduced by local compositional effects at 950ºC and 1050ºC

  22. Summary • Double layered coating with monolithic TiB2 and TiB whiskers was achieved • Unique coating morphologies were seen • Growth of boride layers seems to follow parabolic kinetics: Diffusion-controlled growth of TiB and total thickness • TiB2 layer growth was not parabolic; but could be approximated to thickness ~ D?t1/3

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