Surface Treatment of Titanium

transcript

Christiane JungKKS Ultraschall AG, Steinen SZ

Dr. Christiane Jung, Swiss Tribology Meeting, Murten, 16. November 2007

The Tribology of Precision

Swiss Tribology Meeting

SBB Centre Löwenberg in Murten, Switzerland

16. November 2007

Outline:

1. KKS Ultraschall AG

2. Surface Treatment of Titanium

3Dr. Christiane Jung, Swiss Tribology Meeting, Murten, 16. November 2007

KKS-Ultraschall AGUltrasonic & Surface Technologies

Profile

- Development and Production of Cleaning Units based on Ultrasonic Technology.

- Surface Finish and Cleaning of Metal Parts, in particular of Implants made from Titanium and Stainless Steel.

History

1982: Foundation of the Company KKS Keller H.P. 1999: Change to an „Aktiengesellschaft“

→ KKS Ultraschall AG – Ultraschall & Oberflächentechnik2006: New Building – “Medical Surface Center”2007: 25 Anniversary

Coworkers: ~ 55 (2007)

Medical Surface Center

ProductsUnits for Surface Treatment and Cleaning

Ultrasonic Generators

Small Ultrasonic Bath, 40-95 Liter

Ultrasonic Vibrators

One-Chamber Ultrasonic Unit (Cleaning, Rinsing, Drying) Automated Cleaning Unit

(Cleaning, Rinsing, Passivation, Drying)

Unit for ElectropolishingDry-Blasting Units

Services

Titanium

Stainless steel

Metals

Medical Surface CenterSurface Treatment of Implants and Instruments made from Titanium and Titanium Alloys

Titanium

Surface properties are important !

1. Protective effect (P)- chemical resistance; friction; wear; hardness; ….

The PDF-Effect of the Surface

„Surface Treatment“

2. Decorative effect (D)- color; brightness; haptic ….

3. Functional effect (F)- improvement of the interaction with other materials(i.e. metals, polymers, biological tissues, bone …)

Outline:

2. Surface Treatment of Titanium

2.1. Passive Layer

2.2. Color-Anodizing (KKS01, TioCol)

2.3. Importance of Mechanical Pretreatment (KKS00)for the Quality of Color-Anodized Surfaces

2.4. Dark-Anodizing (KKS02, TioDark)

2.1.1. The natural passive layer

Titanium + Oxygen ⇒ Titanium dioxide (natural oxidation)

[ Ti ] + [ O2 ] ⇒ [ TiO2 ]

titanium substrate

Titanium dioxide passive layer(TiO2)

(~ 5 nm thickness)

2.1.2. The artificial passive layer

natural passive layer

titanium substrate

artificial passive layer

titanium substrate

Electrochemical Oxidation(„Anodizing“)Thermal OxidationChemical Oxidation

Oxidizing agents such as:

Nitric acid (HNO3)Hydrogen peroxide (H2O2)Thickness < 40 nm

2.1.3. Electrochemical Oxidation („Anodizing“)

Thicker passive layer (up to ~ 300 nm)Protection against further corrosion.

Protective Effect

Functional EffectDecorative Effect

Color-Anodizing

Dr. Christiane Jung, Swiss Tribology Meeting, Murten, 16. November 2007“TioCol”

2.2. Color-Anodizing (KKS01, TioCol) start

Electrochemical cell

2.2. Color-Anodizing (KKS01, TioCol) step 1

2.2. Color-Anodizing (KKS01, TioCol) step 2

Increase of layer thickness changes the colordue to light ray interference.

Gasoline on water

Colors are used as codes for implants and tools.

Medical Surface Center

Electrochemical Cells

Surface roughnessRa ~0.045 - 0.100 µm

Side-view topography

2.4. Importance of mechanical pretreatment ( KKS00 ) for the quality of color-anodized surfaces

grinding media

High brightness of the surfaces

Microcrystals acting as grinding and polishing particles ? microscopic images; magnification 500

pH ~ 5

Magnification 63

Granulate

impregnated with wax, plant and mineral oils, fatty acids, emulsifier, and oxides as grinding particles

Pretreatment with small-sized granulate combines mechanical with chemical treatment ?

Surface Roughness of Titanium Discs

Ti 6Al 7Nbbefore anodizingsRa = 0.047 µm

color-anodized at 62 V sRa = 0.045 µm

(polished with granulate)

2.4. Dark-Anodizing (KKS02, TioDark)

Main steps for Dark-Anodizing (KKS02, TioDark)

Oxygen evolutionColor formation

Titanium substrate

Conversion layer

Porous outermost layer

Start Sparking

Increasing voltage

Raster Electron Microscopic Picture(cpTi, grade 2)

Titanium substrate

Conversion layer

Porous outermost layer

before anodizing

Examples for dark-anodized titanium surfaces( TioDark )

(Ti 6Al 4V, porous layer removed)

afterbefore

before

before after

afterbefore

sRa = 0.241 µm sRa = 0.327 µm

Surface Topography of untreated and dark-anodized Ti 6 Al 4 V - samples

sRa ~ 0.24 – 0.40 µm

Surface roughness for different samples of cpTi (grade 2 & 4), Ti6Al4V, Ti6Al7Nb)

before after

afterbefore

Surface characterization by Raman spectroscopy

Rutile TiO2 Anatase TiO2Suggested assignment:Contributions of:

31Dr. Christiane Jung, Swiss Tribology Meeting, Murten, 16. November 2007

Scratch testdark-anodized sample scratches color-anodized sample

(Ti 6Al 4V / Ti 6Al 4V - pair)

Scratch spots:Magnification: 63

Surface of dark-anodized sampleMagnification 63

Ti 6Al 4V

expected color in scratch spot

33Diamond cone 90°; velocity: 0.1 mm/s; distance: 5 mm; zero load: 1.0 mN; load: 20 mN; load cycles: 10

Scratch test(diamond / cpTi grade 4 - pair)

Dependence of the friction coefficient on the sliding distance

CSM: standard tribometer, „ball on disc“ method

ball: steel 100Cr6

Friction: Steel/Titanium – Pair

Initial friction coefficientsliding distance = 6.7 mm, scaled to untreated surfaces

CSM standard tribometer

ball: steel 100Cr6, 6mm ∅, dry; linear mode, ½ amplitude: 2mm, max linear speed: 2 cm/s, normal load: 250 mN, cycles: 470, acquisition rate: 10 Hz, temperature: 25°C, atmosphere: air, huminity: 35%CSM: standard tribometer, „ball on disc“ method

Comparison: CSM nano tribometer (20 mN load) and standard tribometer (250 mN load)

Initial friction coefficientscaled to untreated surfaces

Steel/Titanium Pair

CSM nano tribometerDr. Christiane Jung, Swiss Tribology Meeting, Murten, 16. November 2007

Nano- and micro-hardness of dark-anodized surfaces.

Indentation profil

Lower initial friction coefficient.

Increased micro- and nano-hardness.

Increased layer thickness.

Very good haptic.

Dense, dark and low-reflective

Biocompatible

compared to untreated surfaces

TioDark

Summary

Surface Treatment

A great challenge

Acknowledgement

CSM (Micro- and nano-hardness; tribology studies)

INNOWEP (Nano-scratch test, wear rate)

CSEM (Thickness measurements)

SGS Institute Fresenius (XPS depth profile analysis)

Fachhochschule der Nordwestschweiz (REM/EDX)

Technical University Berlin, Institute for Chemistry (Raman spectroscopy)

FRT Suisse AG (Surface topography analysis)

Surface Treatment of Titanium

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