Transcript Combating challenges... - Institute of Materials Finishing

Novel Surface Coating Technology of Light Alloys
for the Aerospace Industry
*Suman Shrestha
Stephen Hutchins
Victor Samsonov
Oleg Dunkin
IMFAIR 2009
Surface Coating/Surface Engineering for the Aerospace Industry
10-11 June 2009
© Keronite 2009
Scope
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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
Al, Mg, Ti
Strength and weakness
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Abundant elements in the Earth’s crust
Low 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 ability
Good mechanical and physical properties
Various manufacturing / processing routes e.g. extrusion, rolling, cast, forgings,
powder metallurgy, injection moulding, spraying (near net shape), advanced
joining techniques
Recyclability
Poor corrosion/wear – thermodynamically reactive – Mg
Poor corrosion/wear / abrasion / erosion-corrosion – Al
Fretting / impact wear, cold welding – Ti
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Challenges:
Technological, commercial, environmental…
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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 parts
Cost effectiveness, commercial viability, sustainability and availability
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
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Multifunctional requirements
Light
alloys
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Problems
Any mechanism which has surfaces that require separation e.g.
deployment, hold down points, relays, end stops
Effect under vacuum - contacting parts may stick together
Unexpected separation forces are necessary for opening
Separation force > Opening force
Cold 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’
Reference: ECSS - E30, Part 3A, section 4.7.4.4.5 “Separable Contact surfaces”
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Problems
Magnesium – Light weight & high strength
Highly prone to corrosion
Alloy – ZE41A-T5
Courtesy: DSTO, Australian Government DoD
Costs
New MRGB – approx US$1.2M
Repair MRGB – US$400K
1997-2002 – 37 MGB repaired or replaced
2003-2008 – 12 repaired or replaced
Main Rotor Gearbox
Corrosion Prone Areas
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Cadmium plated steel inserts
Forward Bridge Mounting Pad
Coating processes for aluminium
Processes
Anodising
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Sulphuric acid
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Phosphoric acid
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Chromic acid
Plasma electrolytic oxidation
Up to100m
Keronite
and 2000HV
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Thickness up to 50m
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Hardness up to 500HV
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Concentrated acid based
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Keplacoat
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Environmentally
friendly
Thickness up to 40m
Hardness up to
1000HV
Coating processes for magnesium
Processes
Conversion
Chromating
Anodising
Advanced Electrolytic
oxidation
HAE
Keronite PEO
Phosphating
DOW
MAO Tagnite
Environmental
concerns
Environmental
concerns
Anomag ?
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MAO Magoxid
coat
Environmentally
friendly
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
Conventional anodising process
Anodic oxidation
Substrate dissolution
Gas evolution
Dielectric breakdown
Electrolyte
e.g. H2SO4 (conc.)
Passive oxide film
Aluminium substrate
1 µm
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Plasma electrolytic oxidation
Anodic oxidation
Substrate dissolution
Gas evolution
Dielectric breakdown
Plasma processes
Alkaline electrolyte
Free of Cr, heavy metal
Cathodic processes
Electrophoresis
Melt flow & solidification
High Frequency/Field effects
Aluminium substrate
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© Keronite 2008
2009
20 m
Structure & composition
– Al substrate
20 m
● a-Al2O3
○ g-Al2O3
□ Al
anodic coating:
Standard
Amorphous Al2O3
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Structure & composition – Mg substrate
PEO
Dow 7 dichromate
on AZ91D
20 µm
10 µm
20 µm
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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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Salt fog / humidity endurance
Salt fog endurance, hrs at a
Rating of 9
AZ91D uncoated / 220 hrs
Dow 7 on AZ91D / 220 hrs
KTM (AZ91D) G3M 7 / 220 hrs
Keronite 12-15um+PC
Keronite 5-7um+PC
Keronite 12-15um
KTM (AZ91D) G3M 7 PC / 2000 hrs
Keronite 5-7um
Dow 7 10-12um
0
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500
1000 1500 2000
KTM (AZ91D) G3M 7 PC / 500 hrs to
40C, 98%RH, DIN 50017KK
Environmental resistance
a)
b)
Surface of a) *uncoated AA7075 alloy; (b)
Impregnated Keronite; and (c) hard-anodised
coating on AA7075 after 50 thermal shocks (196 and +100C) followed by 360hrs of salt
spray exposure * - uncoated alloy was not
subjected to thermal shock
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c)
Corrosion
at edge
Keronite
Hard
anodised
Protection against impact wear
G2 Keronite/2219
Hard anodised/2219
G3 Keronite/AA2219
Ref: Shrestha et al., Proc. of 9th Intl Symposium on Materials in a Space Environment, 16-20 June 2003, The
Netherlands, p.57-65.
© Keronite 2009
Protection against cold welding
Survey of
of maximum
maximum adhesion
adhesion forces
forces for
for several
several bulks
bulks and
and coatings
coatings
Survey
0
0
2000
2000
4000
4000
6000
6000
8000
8000
10000 12000
12000 14000
14000
10000
mN
mN
SS17-7PH // SS17-7PH
SS17-7PH
SS17-7PH
13359
13359
SS17-7PH +MoS2
+MoS2 // SS17-7PH
SS17-7PH
SS17-7PH
AISI440C // AISI440C
AISI440C
AISI440C
5870
5870
324
324
AL7075 // AL7075
AL7075
AL7075
High adhesion for uncoated specimens
7330
7330
AL7075+NiCr-pl. // AL7075+anodised
AL7075+anodised
AL7075+NiCr-pl.
100
100
AL7075+Anodised // SS15-5PH
SS15-5PH
AL7075+Anodised
242
242
AL2219+Keronite 2nd
2nd // AISI
AISI 52100
52100
AL2219+Keronite
107
107
AL2219+Keronite 2nd
2nd // AISI
AISI 52100
52100
AL2219+Keronite
110
110
Severe destruction of coating
No destruction of coating
2219+Keronite 2nd
2nd // AL2219+Keronite
AL2219+Keronite 2nd
2nd
329
2219+Keronite
329
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.
© Keronite 2009
Coatings for low friction
 Rolling friction wear test
0.6
 -196˚C
 300
rpm
 30,000 revolutions
 Keronite on AA6061
 50µm thickness coating
 Similar counter bodies
Friction Coefficient
 500N
0.5
0.5
0.4
Keronite composite
0.3
*
0.2
0.12
0.1
0.08
0.06
0.04
10e-2 mbar
10e-4 mbar
0
Polished
Keronite
ambient
lab/vacuum
*
Courtesy: European Space Agency
Courtesy: Instituto de Astrofísica de Canarias
© Keronite 2009
1000 mbar
1 mbar
Tribological applications
Keronite vs HVOF Al2O3 and Ni-SiC
TE77 high frequency friction machine
Bench-scale dynamometer
PEO(BO)
Ni-SiC(BO)
PEO(BO+FM)
Ni-SiC(BO+FM)
Friction Coefficient
0.15
0.1
0.05
0
0
© Keronite 2009
10
20
Time (Hours)
30
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
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Courtesy: University of Bologna
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 hardwares
Extreme 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
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 microcalorimeters 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
MEDET in Shuttle Payload Bay
[email protected]
© Keronite 2009