Novel Doublelayered Titanium Boride Coatings on Titanium Kinetics

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 - 134 th Annual Meeting and Exhibition Supported by: Utah State Center of Excellence Ortho Development Corporation Feb. 15, 2005 TMS 2005

Outline • Overview • Motivation for research • Experimental: • Boron diffusion treatment • Results: • Temperature and time effects • Double layer coating morphology • Layer growth kinetics • Conclusions Feb. 15, 2005 TMS 2005 2

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 Feb. 15, 2005 TMS 2005 3

Surface modification processes • Laser and Electron techniques Beam based • Ion Implantation • Physical Vapor Deposition • Chemical Vapor Deposition • Diffusion treatments – Preferred Ø Method analogous to carburizing of steel is advantageous Titanium boride (Ti. B) on titanium? Feb. 15, 2005 TMS 2005 4

What is Ti. B and Ti. B 2? • Hard titanium compounds Crystal structure of Ti. B and Ti. B 2 Ti-B phase diagram • Ti. B at 18 -18. 5%B • Ti 3 B 4 at 22. 4%B • Ti. B 2 at 30. 1 -31. 1%B Feb. 15, 2005 TMS 2005 5

Research Focus • In-situ creation of Titanium Boride (Ti. B) whiskers in Ti and Titanium Diboride (Ti. B 2) • High elastic modulus (E of Ti. B = 370 GPa) • High Vickers hardness of Ti. B (Hv ~ 1800@1 kg load) • High Vickers hardness of Ti. B 2 (Hv ~ 3200@1 kg load) • “Clean” Ti-Ti. B interface • Develop an “integral” boride coating Feb. 15, 2005 TMS 2005 6

Experimental • Polished Ti-6 Al-4 V 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 Feb. 15, 2005 TMS 2005 7

Ti. B 2 layer X-Ray analysis Ti. B whisker As-treated surface After removing 20 mm Feb. 15, 2005 TMS 2005 8

Temperature effects 10 mm 950ºC for 24 hours 1050ºC for 24 hours 1100ºC for 24 hours 1200ºC for 24 hours Feb. 15, 2005 TMS 2005 9

Effect of time at 1050ºC 10 mm Feb. 15, 2005 3 hours 6 hours 12 hours 24 hours TMS 2005 10

Ti. B 2 thickness variation Ø Ø Monolithic (Ti. B 2) thickness (mm) Time (h) 950ºC 1050ºC 1100ºC 1200ºC 3 2. 6 9. 2 9. 1 7. 8 6 4 10 9. 5 13. 4 12 6. 3 8. 5 10. 7 14 18 5 11. 2 11. 1 14. 6 24 7 11 13. 9 17. 9 At a fixed temperature, Ti. B 2 thickness increases by a maximum of 10 mm from 3 to 24 hours The thickness variation depends on the treatment temperature Feb. 15, 2005 TMS 2005 11

Monolithickness (mm) Ti. B 2 thickness variation Time (h) Feb. 15, 2005 TMS 2005 12

Monolithickness cubed (mm 3) Ti. B 2 thickness variation Time (h) Feb. 15, 2005 TMS 2005 13

Ti. B thickness variation Ø Ø Ti. B thickness (mm) Time (h) 950ºC 1050ºC 1100ºC 1200ºC 3 8. 1 13 7. 8 11. 3 6 14. 4 16. 2 10. 8 11. 3 12 17. 3 23. 2 15. 8 21. 7 18 23. 7 20. 4 18. 9 17. 1 24 27. 4 22. 7 23. 7 26. 9 At a fixed temperature, Ti. B thickness increases significantly from 3 to 24 hours The thickness variation depends on the treatment temperature and time Feb. 15, 2005 TMS 2005 14

Ti. B thickness (mm) Ti. B thickness variation Time (h) Feb. 15, 2005 TMS 2005 15

Parabolic diffusion? Ti. B thickness squared (mm 2) Ti. B thickness variation with temperature and time ? ? Time (h) Feb. 15, 2005 TMS 2005 16

Double layer thickness variation Ø Ø Total (Ti. B+Ti. B 2) thickness (mm) Time (h) 950ºC 1050ºC 1100ºC 1200ºC 3 10. 8 22. 8 17. 3 19. 7 6 12 27 18. 8 26. 4 12 22. 8 31. 4 26. 3 35 18 28. 5 31. 1 38. 3 24 40. 2 39 36. 4 45. 3 At a fixed temperature, total (Ti. B+Ti. B 2) thickness increases significantly from 3 to 24 hours Total thickness increases with increasing combination of time and temperature Feb. 15, 2005 TMS 2005 17

Total coating thickness (mm) Double layer thickness variation Time (h) Feb. 15, 2005 TMS 2005 18

Kinetics of Double Layer Total thickness squared (mm 2) Total thickness variation with temperature and time Time (h) Ø Parabolic growth behavior: Diffusion-controlled boride layer growth Feb. 15, 2005 TMS 2005 19

Process Model Thin Ti. B 2 layer Increasing Ti. B 2 layer Slowly increasing Ti. B Small Ti. B Increasing 2 layer Thicker Ti. B whiskers Powder pack Alloy matrix Alloymatrix *Illustrations not to scale Feb. 15, 2005 TMS 2005 20

Some Interesting observations • Ti. B 2 thickness increases with T for a given time • Lower T, Shorter t, thinner Ti. B whiskers • Inconsistent trends at 1050 and 1100ºC: Shorter times: Ti. B layer thickness at 1050ºC > than at 1100ºC Longer times: Ti. B layer thickness at 1050ºC < than at 1100ºC • Beta transus ~1010ºC: • Variability introduced by local compositional effects at 950ºC and 1050ºC Feb. 15, 2005 TMS 2005 21

Summary • Double layered coating with monolithic Ti. B 2 and Ti. B whiskers was achieved • Unique coating morphologies were seen • Growth of boride layers seems to follow parabolic kinetics: Diffusion-controlled growth of Ti. B and total thickness • Ti. B 2 layer growth was not parabolic; but could be approximated to thickness ~ D? t 1/3 Feb. 15, 2005 TMS 2005 22