Preparation and characterizations of new coatings …...[1] L. BESRA, Application of constant...

Preparation and characterizationsof new coatings based on PTFE-anodic films

for the improvement of the tribological behavior of aluminum substrate

L. ARURAULT, J. ESCOBAR, V. TURQ, P-L. TABERNA

IHAA 2014 – 15th Technical Symposium

New York, September 24-26, 2014

2New York, September 24-26, 2014 IHAA 2014 L. ARURAULT

Background

• 1960: Tefal (contraction of Teflon and aluminum) prepares non stick pan with PolyTetraFluoroEthylene (PTFE) or Teflon© coatings [2,3]

[1] F. KELLER et al. - Structural Features of Oxide Coatings on Aluminum, J. Electrochem. Soc., 100, 1953, 411.[2] M. GREGOIRE & HARTMANN (TEFAL) - Perfectionnement aux traitements de surfaces des métaux - FR 1 236 019(1959)[3] TEFAL - Produit en polytétrafluoroéthylène et son procédé de fabrication - FR 1 260 025(1959)[4] H. WANG et al. - Applied Surface Science, Vol.252 (2005), 1662[5] H. WANG & H. WANG - Applied Surface Science, Vol.253 (2007), 4386

• H. Wang et al. [4,5] performed heat treatment to incorporate melted PTFE into the pores

• Actual PTFE coatings:

⇒ Non stick properties

⇒ Limit the wear of parts

⇒ Only on the top surface

Ideal microstructure [1]

Objectives: Functionalize an anodic film with PTFE particles into the pores

⇒ Enhance the lifetime/ limit wear of mechanical parts⇒ Limit energy dissipation

Anodizing : Preparation of an oxide film on a metal surface⇒ Thermal and electrical insulation⇒ Enhancement of corrosion resistance⇒ Functionalization


Approach

• Substrates Al 1050 and Al 7175 T7351

• Pretreatments

– Clean the surface

• Anodizing

– An anodic film with a thickness of about 10 µm and a pore diameter of about 200 nm

• Functionalization

– Incorporate PTFE particles into the porous structure

• Characterizations

– Microstructure

– Tribological tests (friction and wear)

SubstrateSubstrate

10µm

⇒ Improved sedimentation

⇒ Electrophoretic Deposition


Anodizing

• 1050 Aluminum alloy (99.5% Al)

• Pretreatments (ESA notification ECSS Q70-03A)

• Anodizing

• Preparation of a porous anodic film

on 1050 aluminum alloy

• Two antagonistic reactions :

• Electrochemical growth of the oxide film

• Chemical dissolving of the film

by acidic electrolyte

2Al + 3H2O → Al2O3 + 6H+ + 6e-

Al2O3 + 6H+ → 2Al3+ + 3H2O

Magnetic stirrer

+-

Magnetic stirring bar

Water circulation

Cathode (Pb)

Anode (Al)

Electrolyte (H3PO4)

Degreasing Etching Neutralization

EthanolNa2CO3 (6.2 g.L-1)Na3PO4 (12.5 g.L-1)

5 min. at 93°C

HNO3 (50%v/v)3 min. at ambient T°C

Ra ≈ 0.3 µmPV ≈ 3 µm

Ra ≈ 0.6 µmPV ≈ 8 µm

Ra ≈ 0.6 µmPV ≈ 10 µm


• Parametric study

⇒H3PO4 (0.4M), Current density 1.4 A/dm², bath temperature 20°C, Time 34 min

⇒ Thickness of 10.0 ± 0.5 µm and pore diameter of about 200 ± 15 nm

a b

200 nm 1 µm

Anodizing


0

5

10

15

20

20 40 60 80 100 120 140 160 180 200 220 240 260 280 300

Inte

nsity

(%

)

Size (d.nm)

Size Distribution by Intensity

Record 1: ptfe50_70 1

FunctionalizationImproved sedimentation technique

• PolyTetraFluoroEthylene (PTFE) aqueous dispersion

� Surfactant : alkyl polyglycol ether� Zeta potential: - 45 mV

• Incorporation technique• Improved sedimentation technique

Total evaporation

PTFE dispersion

Hot plate

PTFE particles

Bain-marie at 60°C

Particle size (nm)

Inte

ns

ity (

%)

Hot plate

Anodized aluminum


⇒ Incorporation of PTFE particlesinto the pores and on the surface

200 nm

1 µm

1 µm

FunctionalizationImproved sedimentation technique

J.ESCOBAR et al., Improvement of the tribological behaviour of PTFE-anodic film composites prepared on 1050 aluminum substrate, Appl. Surf. Sci. 258 (2012), 8199-8208.


• Tribology

Tribological characterizationsAnodized Al and PTFE plate

Aluminum: Friction coefficient : 0.7 – 0.8

Anodized Al: Friction coefficient : 1.1Lifetime: 3000 cycles

PTFE plate: Friction coefficient : 0.1

Metallic scraps on the ball→ Aluminum is exposed

Optical microscopy after 5000 cycles on the anodic film

Ball

Optical microscopy after 5000 cycles on the PTFE plate

PTFE scraps on the counterfaceNot visible track on PTFE plate

Friction coefficient

FT

FN

Track

Ball Track

µ = FT

FN

• Anodized Al and PTFE plateRotative mode , radius 5 mm; speed = 5.04 cm/s; alumina counterface, FN=1N

Number of cycles: 5000

Slidingdirection


• Tribology– Track radius: 5 mm; Speed= 5.04 cm/s; Alumina counterface, FN=1N

Period 2: Friction coefficient between 0.17 and 0.90

⇒ Composite PTFE/ anodic film• Improvement of the anodic film lifetime by 3

Tribological characterizationsImproved sedimentation technique

Period 1: friction coefficient ≈ 0.17

⇒ PTFE on top surface, length depends on the PTFE coating thickness

Period 3: friction coefficient = 0.90-1.00

⇒ Aluminum + alumina fragments• Improvement of the total lifetime by at least 20

Ball Ball

Track Track

PTFE surface PTFE inside

IAl

= 0.072 = 0.401IF

IAl

IF

Localized EDX on the center of the track


• Electrophoretic Deposition (EPD)

– A voltage (or a current) is applied between two immersed electrode in a dispersion

– Advantages:

• Higher deposition rate

• Homogeneity of the deposit

• Suitable for complex shaped surface

At the cathode :

2H2O (l) + 2e-

H2 (g) + 2 OH-(aq)

At the anode :

2H2O (l)

O2 (g) + 4 H+ + 4e-

Oxygen evolutionHydrogen evolution

+ -

Water

CathodeAnode

PTFE aqueous dispersion

FunctionalizationElectrophoretic Deposition


• Cathodic EPD– Use of cationic surfactant to change the zeta potential

• Cetyl TriméthylAmmonium Bromide (CTAB)

+

+

+

+

+ +

Particles size Zeta Potential

Solution without CTAB 90 ± 40 nm - 45 mV

Solution with CTAB 90 ± 40 nm + 55 mV



• Electrophoretic Deposition– Cathodic EPD: PTFE + CTAB dispersion

⇒ No particles neither inside the pore nor on the surface

⇒ Aggregated particles on the top surface

⇒ Low efficiency for low voltage ⇒ Gas bubbles production avoids the incorporation of the particles and can leads to an aggregation of the particle [1]

U = -0.5 and -2 V t = 5h

[1] L. BESRA, et al., Experimental verification of pH localization mechanism of particle consolidation at the electrode/solution interface and its application to pulsed DC electrophoretic deposition (EPD), J . Eur. Ceram. Soc. 30 (2010) 1187–1193


- 2V-0.5V


• Besra et al. found a way to make bubble free deposit by EPD with aqueous dispersion [1]

– Use of pulsed current on a plan surface

4 main parameters:

- Voltage

- Pulse frequency

- Pulse duty cycle (Ton / (Ton+Toff))

- EPD duration

Objectives:

- Incorporate the PTFE particles by using pulsed voltage- Improve homogeneity, efficiency and elaboration time

[1] L. BESRA, Application of constant current pulse to suppress bubble incorporation and control deposit morphology during aqueous electrophoretic deposition (EPD), J . Eur. Ceram. Soc. 29 (2009) 1837–1845


Time

Cu

rre

nt

Toff

Ton


• Pulsed voltage EPD Voltage (V) Frequency (Hz) Duty cycle (%) Duration (min)

60 0.5 50 30 min

- Incorporation of PTFE into the pores



Conclusion/Prospects

• Incorporation of PTFE particles inside the porous structure by using improved sedimentation technique

– Reduction of the friction coefficient from 1.1 to 0.5 - 0.6

– 3-fold improvement of the lifetime of the anodic film

– Drawbacks: Non-homogenous deposit , elaboration time , suitable for plan surface only

• Electrophoretic deposition– Constant voltage leads to bubble production and avoids PTFE particles incorporation

– Incorporation of particles was obtained by using pulsed voltage

• Tribological tests on EPD tests (in progress)

• Tests on Al 7175 T3 (in progress)


Thank you!

Pr. Laurent [email protected]

CIRIMAT, University of Toulouse, France

J.ESCOBAR, L.ARURAULT, V.TURQ, Improvement of the tribological behavior of PTFE-anodic film composites prepared on 1050 aluminum substrate, Appl. Surf. Sci. 258 (2012), 8199-8208.

J.ESCOBAR, L.ARURAULT, V.TURQ, P-L.TABERNA, Study of electrophoretic deposition of PTFE particles on porous anodized aluminum, Submitted

Preparation and characterizations of new coatings …...[1] L. BESRA, Application of constant...

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