© Keronite 2009 *Suman Shrestha Stephen Hutchins Victor Samsonov Oleg Dunkin IMFAIR 2009 Surface Coating/Surface Engineering for the Aerospace Industry.
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© Keronite 2009
*Suman ShresthaStephen HutchinsVictor Samsonov
Oleg Dunkin
IMFAIR 2009Surface Coating/Surface Engineering for the Aerospace Industry
10-11 June 2009
Novel Surface Coating Technology of Light Alloys for the Aerospace Industry
© Keronite 2009
Scope
Light alloys strength, weakness and challenges Multifunctional requirements Current technologies and challenges Plasma electrolytic oxidation (PEO) Some test data and recent aerospace applications
© Keronite 2009
Abundant elements in the Earth’s crustLow densities (2.7, 1.7, 4.5g/cm3 vs ~ 7.9g/cm3 of steel)Good to high specific strength (strength-to-weight ratio)Good formability, machinability, alloying abilityGood mechanical and physical properties Various manufacturing / processing routes e.g. extrusion, rolling, cast, forgings, powder metallurgy, injection moulding, spraying (near net shape), advanced joining techniquesRecyclability
Al, Mg, Ti Strength and weakness
Poor corrosion/wear – thermodynamically reactive – MgPoor corrosion/wear / abrasion / erosion-corrosion – AlFretting / impact wear, cold welding – Ti
© Keronite 2009
Challenges: Technological, commercial, environmental…
Meeting environmental/RoHS/recycling legislations such as requirements to replace coating processes of environmental issues e.g. Cd plating, hard Cr plating, acid processes (conc. HNO3, H2SO4, HF), solvent, other heavy metals
Search for advanced surface technologies continues to meet increasing challenges and obtain multifunctional coatings
Amendments to MIL-A-8625E, AMS 2470, AMS 2466, ECSS-Q-7-71A required
Continuous requirements to reduce vehicle weight and fuel efficiency Surface treatment to achieve enhanced multifunctional properties Surface engineering of Ti – Plating (low bond strength), plasma nitriding (low fatigue), PVD (low load-bearing capacity), anodising (only as pre-treatment),
thermal spraying (difficulty with complex shapes)Capability to coat large and complex partsCost effectiveness, commercial viability, sustainability and availability
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Multifunctional requirements
Corrosion e.g. general, SCC, galvanic, fatigue
Wear e.g. fretting, impact, sliding,
friction etc Dielectric / Electrical conductance
Thermal conductance /barrier
Thermo-optical properties e.g. solar absorptance, thermal
emittanceEnvironmental degradation e.g. humidity,
thermal shocks, UV, atomic oxygen in LEO
Debris and Outgassing leading to
contamination at sensitive and operational
surfaces
Aluminium alloys
Cold welding / seizure
Pre-treatment for paints/adhesive Light
alloys
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Problems
Reference: ECSS - E30, Part 3A, section 4.7.4.4.5 “Separable Contact surfaces”
Any mechanism which has surfaces that require separation e.g. deployment, hold down points, relays, end stopsEffect under vacuum - contacting parts may stick together Unexpected separation forces are necessary for openingSeparation force > Opening forceCold welding with failure of mechanism
Mechanism of a satellite: anchor actuated from rest position (middle) electromagnetically. Impacts on both sides resulted in ‘seizing’ by ‘cold welding’
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Problems
Magnesium – Light weight & high strengthHighly prone to corrosionAlloy – ZE41A-T5
Main Rotor GearboxCorrosion Prone Areas
Forward Bridge Mounting Pad
Cadmium plated steel inserts
CostsNew MRGB – approx US$1.2MRepair MRGB – US$400K1997-2002 – 37 MGB repaired or replaced2003-2008 – 12 repaired or replaced
Courtesy: DSTO, Australian Government DoD
© Keronite 2009
Coating processes for aluminium
Processes
Anodising Sulphuric acid
Phosphoric acid
Chromic acid
Plasma electrolytic oxidation
Keplacoat
Keronite
Environmentally friendly
Thickness up to 50m
Hardness up to 500HV
Concentrated acid based
Thickness up to 40m
Hardness up to 1000HV
Up to100m
and 2000HV
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Coating processes for magnesium
Processes
Conversion Anodising Advanced Electrolytic oxidation
Chromating
Phosphating
HAE
DOW
Environmental concerns
Anomag ?
MAO Tagnite
Keronite PEO
Environmentally friendly
MAO Magoxid coat
Environmental concerns
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Keronite PEO
Cambridge (UK) – based company, specialising in advanced plasma electrolytic oxidation (PEO) technology and its
application to a wide range of industry
R&D and applications engineering for multifunctional surfaces
Provide solutions for light alloys via surface engineering
© Keronite 2009
Aluminium substrate
Electrolytee.g. H2SO4 (conc.)
Passive oxide film
1 µm
Anodic oxidation
Substrate dissolution
Gas evolution
Dielectric breakdown
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Conventional anodising process
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Anodic oxidation
Substrate dissolution
Gas evolution
Dielectric breakdown
Alkaline electrolyteFree of Cr, heavy metal
Aluminium substrate
Anodic oxidation
Substrate dissolution
Gas evolution
Dielectric breakdown
Plasma processes
Cathodic processes
Electrophoresis
Melt flow & solidification
High Frequency/Field effects
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Plasma electrolytic oxidation
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● -Al2O3
○ -Al2O3
□ Al
20 m
20 m
Standard anodic coating:Amorphous Al2O3
Structure & composition – Al substrate
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Mg components
10µm Keronite coating on AZ31
10µm Anomag coating on AZ31
10 cycles of thermal shock (-196 and +100ºC) followed by 336hrs of exposure to ASTM B117
10µm Keronite treated Elektron 21 alloy after 154 hrs of ASTM B117
AZ91C uncoated, 10µm Keronite, 20µm Keronite after 120 hrs of B117
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AZ91D uncoated / 220 hrs
Salt fog / humidity endurance
Dow 7 on AZ91D / 220 hrs
KTM (AZ91D) G3M 7 PC / 2000 hrs
KTM (AZ91D) G3M 7 PC / 500 hrs to 40C, 98%RH, DIN 50017KK
KTM (AZ91D) G3M 7 / 220 hrs
0 500 1000 1500 2000
Dow 7 10-12um
Keronite 5-7um
Keronite 12-15um
Keronite 5-7um+PC
Keronite 12-15um+PC
Sa
lt fo
g e
nd
ura
nce
, hrs
at a
R
atin
g o
f 9
© Keronite 2009
KeroniteHard
anodised
Surface of a) *uncoated AA7075 alloy; (b) Impregnated Keronite; and (c) hard-anodised coating on AA7075 after 50 thermal shocks (-196 and +100C) followed by 360hrs of salt spray exposure * - uncoated alloy was not subjected to thermal shock
b)a)Corrosion at edge
c)
Environmental resistance
0
500
1000
1500
2000
Sal
t fo
g ex
posu
re. hr
s aa
KeronitePEO(2219)
unsealed
KeronitePEO(2219)sealed
KeronitePEO(7075)
unsealed
KeronitePEO(7075)sealed
Hardchrome
Electrolessnickel
Hardanodised(7075)sealed
Uncoated7075
© Keronite 2009
Protection against impact wear
G2 Keronite/2219 Hard anodised/2219
Ref: Shrestha et al., Proc. of 9th Intl Symposium on Materials in a Space Environment, 16-20 June 2003, The Netherlands, p.57-65.
G3 Keronite/AA2219
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Protection against cold welding
Survey of maximum adhesion forces in fretting for several bulk materials and for coatings on aluminium (disc / pin). Effect of steel type: AISI 440C shows less adhesion than SS17-7 PH. All coatings on aluminium prevent cold welding. Advantage of Keronite: No destruction of coating.
Shrestha et al., Proc. of 9th Intl Symposium on Materials in a Space Environment, 16-20 June 2003, The Netherlands, p.57-65.
100
242
107
110
0 2000 4000 6000 8000 10000 12000 14000
SS17-7PH / SS17-7PH
SS17-7PH +MoS2 / SS17-7PH
AISI440C / AISI440C
AL7075 / AL7075
AL7075+NiCr-pl. / AL7075+anodised
AL7075+Anodised / SS15-5PH
AL2219+Keronite 2nd / AISI 52100
AL2219+Keronite 2nd / AISI 52100
AL2219+Keronite 2nd / AL2219+Keronite 2nd
13359
5870
324
7330
0 2000 4000 6000 8000 10000 12000 14000
SS17-7PH / SS17-7PH
SS17-7PH +MoS2 / SS17-7PH
AISI440C / AISI440C
AL7075 / AL7075
AL7075+NiCr-pl. / AL7075+anodised
AL7075+Anodised / SS15-5PH
AL2219+Keronite 2nd / AISI 52100
AL2219+Keronite 2nd / AISI 52100
AL2219+Keronite 2nd / AL2219+Keronite 2nd
mN
High adhesion for uncoated specimens
No destruction of coating
Severe destruction of coating
© Keronite 2009
Coatings for low friction
Rolling friction wear test -196˚C 500N 300 rpm 30,000 revolutions Keronite on AA6061 50µm thickness coating Similar counter bodies
0.5
0.120.08
0.06 0.04
0
0.1
0.2
0.3
0.4
0.5
0.6
PolishedKeroniteambient
lab/vacuum
1000 mbar 1 mbar 10e-2 mbar 10e-4 mbar
Fri
ctio
n C
oe
ffici
en
tKeronite composite
Courtesy: Instituto de Astrofísica de Canarias
*
* Courtesy: European Space Agency
© Keronite 2009
Tribological applications Keronite vs HVOF Al2O3 and Ni-SiC
Bench-scale dynamometer TE77 high frequency friction machine
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Keronite vs TiN, TiAlN
Cylinder-on-flat disc dry sliding wear 5-35N load Ø40mm steel cylinder plasma sprayed with Al2O3 + TiO2 of 1180 HV 0.6m/s Sliding distance 5000m
Courtesy: University of Bologna
© Keronite 2009
Ceramic coated Al gear mechanisms
Aluminium starter gears, flywheels and clutch discs offer significant mass reductions over steel, and a more durable friction surface
This application reflects the increased hardness, and wear resistance of PEO treated aluminium over that of steel and hard anodising, allowing a much lighter, yet more durable product
The layer’s surface porosity enables impregnation to form a PTFE-based composite layer
Various products boast the durability of steel, together with a reduction in chain wear by a factor of 2-3
© Keronite 2009
Space hardwaresExtreme wear / thermo-optical coatings
Keronite composite coating on EMIR GRISM cryostat wheel bearing currently used for space observation. Courtesy: Instituto de Astrofísica de Canarias
Barrel for satellites treated with new black Keronite. Courtesy: Cilas Marseille
Coarse sun sensor (CSS) Housing treated with black Keronite.
© Keronite 2009
MEDET in Shuttle Payload Bay
Thank you
CNES, ESA, the University of Southampton and ONERA have participated in a cooperative effort to develop a test-bed called the Material Exposure and Degradation Experiment (MEDET)
Keronite coated thermal control micro-calorimeters are mounted on the MEDET flight hardware that is located on the external payload facility of ESA’s Columbus Laboratory on the International Space Station
MEDET was launched on 7th February 2008 and has now been operating since then in orbit
suman.shrestha@keronite.com
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