© 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

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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’

© Keronite 2009

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

© Keronite 2009

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

© Keronite 2009

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

© Keronite 2009

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

© Keronite 2009

Plasma electrolytic oxidation

© Keronite 2009© Keronite 2008

© Keronite 2009

● -Al2O3

○ -Al2O3

□ Al

20 m

20 m

Standard anodic coating:Amorphous Al2O3

Structure & composition – Al substrate

© Keronite 2009

10 µm

20 µm

Dow 7 dichromate on AZ91D

PEO

20 µm

Structure & composition – Mg substrate

© Keronite 2009

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

© Keronite 2009

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

© Keronite 2009

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

© Keronite 2009

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