Preparation and characterizations of new coatings …...[1] L. BESRA, Application of constant...
Transcript of 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
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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
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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
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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
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• 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
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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
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⇒ 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.
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• 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
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• 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
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• 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
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• 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
FunctionalizationElectrophoretic Deposition
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• 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
FunctionalizationElectrophoretic Deposition
- 2V-0.5V
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• 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
FunctionalizationElectrophoretic Deposition
Time
Cu
rre
nt
Toff
Ton
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• Pulsed voltage EPD Voltage (V) Frequency (Hz) Duty cycle (%) Duration (min)
60 0.5 50 30 min
- Incorporation of PTFE into the pores
FunctionalizationElectrophoretic Deposition
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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)
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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