Novel Double-layered Titanium Boride Coatings on Titanium: Kinetics of Boron Diffusion and Coating Morphologies

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?
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What is TiB and TiB2?

• Hard titanium compounds

Ti-B phase diagram
Crystal structure of TiB and TiB2

• TiB at 18-18.5B
• Ti3B4 at 22.4B
• TiB2 at 30.1-31.1B

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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_at_1kg
  load)
• High Vickers hardness of TiB2 (Hv 3200_at_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 950-1200C
• Time at different temperatures 3-24 hours

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X-Ray analysis
TiB2 layer
TiB whisker
As-treated surface
After removing 20mm
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Temperature effects
950ºC for 24 hours
1050ºC for 24 hours
1200ºC for 24 hours
1100ºC for 24 hours
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Effect of time at 1050ºC
3 hours
6 hours
12 hours
24 hours
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TiB2 thickness variation
Time (h) Monolithic (TiB2) thickness (mm) Monolithic (TiB2) thickness (mm) Monolithic (TiB2) thickness (mm) Monolithic (TiB2) 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, TiB2 thickness increases
  by a maximum of 10mm from 3 to 24 hours
• The thickness variation depends on the treatment
  temperature

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TiB2 thickness variation
Monolithic thickness (mm)
Time (h)
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TiB2 thickness variation
Monolithic thickness cubed (mm3)
Time (h)
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TiB thickness variation
Time (h) TiB thickness (mm) TiB thickness (mm) TiB thickness (mm) TiB 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, TiB thickness increases
  significantly from 3 to 24 hours
• The thickness variation depends on the treatment
  temperature and time

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TiB thickness variation
TiB thickness (mm)
Time (h)
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Parabolic diffusion?
TiB thickness variation with temperature and time
?
TiB thickness squared (mm2)
?
Time (h)
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Double layer thickness variation
Time (h) Total (TiBTiB2) thickness (mm) Total (TiBTiB2) thickness (mm) Total (TiBTiB2) thickness (mm) Total (TiBTiB2) 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 31.5 31.1 38.3
24 40.2 39 36.4 45.3

• At a fixed temperature, total (TiBTiB2)
  thickness increases significantly from 3 to 24
  hours
• Total thickness increases with increasing
  combination of time and temperature

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

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Process Model
Illustrations not to scale
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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 gt
  than at 1100ºC
• Longer times TiB layer thickness at 1050ºC lt
  than at 1100ºC
• Beta transus 1010ºC
• Variability introduced by local compositional
  effects at 950ºC and 1050ºC

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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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Activation Energy plots
ln (thickness/time) (cm/sec)
DHTiB 9.3 kJ/mol
DHTiB2 10.7 kJ/mol
1/T(ºK)