Linking Corrosion PhenomenaPrediction to

Corrosion Science andEngineering Fundamentals

R. G. KellyCenter for Electrochemical Sci. & Engr.

Dept. of Materials Sci. & Engr.University of Virginia

Gordon Conference on Aqueous Corrosion 2002

Grand Challenges forCorrosion Science & Engineering• DoD Asset Life Extension

– A/C fleets are aging, must keep operational• How to manage maintenance driven by corrosion?

– New A/C Carrier to be manned by far fewer

• High Level Nuclear Waste Storage– Yucca Mountain Project– Safe storage of nuclear waste for > 104 y

• Civil Infrastructure– New bridges/transportation systems > 80 y service life

A/C Aver. Age* Future PlansKC-135 36 Retain 25+ YrsB-52H 36 Retain 25+ YrsT-38 30 Retain 25+ YrsC-5 20 Retain 25+ YrsC-141B 31 Retire in 8 YrsE-3 18 Retire in 17-25 Yrs* as of 30 Sep 97C-141

KC-135 B-52

Aging Aircraft

KC-135Courtesy D. Peeler

Aging Aircraft Challenge• Corrosion• Fatigue Cracking• Parts Availability• Wiring• Aging Avionics

Repair DensityIncreases

Flow Rates Decrease

Aging Fleet

Modernization$$ Decrease

Mission Capable Rates &A/C Availability Decrease

Maintenance $$ IncreaseCourtesy D. Peeler

Fuselage Floor BeamAA7075-T6 beam + Steel fastener = galvanic corrosion

(from condensation on inside of fuselage)

Courtesy R. Piascik

“Condensed moisture and itscontaminants can be trappedin close fitting, wettablejoints, such as fayingsurfaces and be drawn alongpore lines by capillaryaction.”

FAA Advisory: AC 43-4A (7/25/91)

Classic lap joint corrosion around lower wing access port resulting in pillowing (AA2024)

Courtesy R. Piascik

Occluded Regions Corrode

Currently “Find It-Fix It”Aircraft EntersMaintenance

Corrosion Found (Visual)

Corrosion Repaired

Grind Out,

Check Thickness

Aircraft LeavesMaintenance

Part Replace

Move to “Anticipate & Manage”Aircraft EntersMaintenance

Focus Corrosion Inspection (NDI)

Corrosion Analyzed

Repair

Aircraft LeavesMaintenance

Suppress Defer Repair

or or

Example Hierarchy of Issues forAging Aircraft

• Engineering– What corrosion can we leave & what must be fixed?– What kind of effects does corrosion have on DTDA?

• Applied Science– What chemical variables control the topography and

rate of corrosion in occluded regions?– What properties should be engineered into coating

systems?• Fundamental Science

– What individual electrochemical reactions controlinitial corrosion topography?

– How do we characterize corrosion topography?

Flight Ground Flight Ground.... Specified # Cycles / FH

AssumedDamage Summary Makeup:100% Cyclic

Actual Damage Summary Makeup = ??X % Cyclic Y % Environmental

Actual 1 Calendar Year = 100 Flights, 3 Hours/Flight

Flight Ground Flight Ground

Environmental Cycles

Life Assessment Model AccommodatesTime & Environmental Effects

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 20000 40000 60000 80000 100000 120000

Cycles

C C

rack

Len

gth

B707 Field Aircraft

Analysis if Corroded withPillowing

Mean IDS

Large (99%)IDS = 0.01"

Without Corrosion

Analysis Details:• 0.063" sheet, 3/16 inch fastener, 1" wide ligament• 8.98 ksi R=0 loading• Tension Stress Ratio = 1• Bearing Stress Ratio = 2.72 (countersink effects)• Typical IDS: 0.0033" (APES)• No account for stiffener effects• 545 cycles/year• 7 year protective system breakdown, thickness loss approx. 17.5% at year 42

Analysis Courtesy of Northrop Grumman Corporation and APES, Inc

Life Analysis Compared toB707 Field Aircraft Experience

Topography Affects Local StressIntensities

Time

ThicknessLoss

Time

Pit Size

Time

PillowingStress

Influence onDamage

Time

TopographyCorrection

Examples of Damage Progression DriversRequiring Laboratory and Field Verification

Must transform cartoons to data

KC-135 Doublers

General - no AlcladGeneral - not thru Alclad

20 µm 20 µm

How to Simulate ConditionsInside These Joints?

32 mils

20 µm

Karen LewisJackie Williams

LJ Simulant20 mM Cl-

4 mM NO2-

4 mM HCO3-

2 mM F-

pH 9.0

20 µm

No COx

Same weight loss after 4 months

12 weeks

2 weeks 4 weeks

Development of TopographyWithin Lap Joint

time (weeks)0 2 4 6 8 10 12

% s

urfa

ce a

rea

corro

ded

0

20

40

60

80

100

Ambient CO2

Minimal CO2

Lateral Extent of Corrosion

Development of TopographyWithin Lap Joint

time (weeks)0 2 4 6 8 10 12

dept

h (m

icro

ns)

0

20

40

60

80

100

120

140

Ambient CO2

Minimal CO2Max Depth

Image

2-D AutocorrelationFunction

“Pit” 1200 grit polish

Classification of Corrosion TopographyUsing the Autocorrelation Function

Determination of τ from ACF τ = correlation length

τ∗

T=τmax/τmin

Pitted 304 Stainless Steel

T ratio = 0.94

τ = 17.35 µm

Electropolished Cu

T ratio = 0.95

τ = 0.59 µm

Classification of CorrosionTopography

polished< 1 µm> 0.5

pitting>1 µm> 0.5

mill finish<1 µm< 0.5

general corrosion>1 µm< 0.5

SurfaceClassification

τ*maxT Ratio

T(t) forCorroding Lap Joint Faying Surfaces

Role of Carbon Dioxide SystemDestabilization of Pits

time (weeks)0 2 4 6 8 10 12 14

pit a

spec

t rat

io

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

minimal COx

LJSS

Role of Carbon Dioxide SystemInhibition of Cathodic Reaction

Al metal bulkAl metal bulkAl metal bulk

4. 4. Stable pitting Stable pitting

Cl- Na+ H2O Oxide Layer (Al2O3)H+ Al3+

Al metal bulkAl metal bulk

BeginningBeginning

1. 1. ClCl-- adsorption adsorption2. 2. Passive film breakdownPassive film breakdown3. 3. DDissol’nissol’n//repassivationrepassivation

Al metal bulk

Atomistic Framework of Pitting

Donghai Mei

Matt Neurock

KMC Modeling of Pitting of Al and Al/Cu in Chloride SolutionKMC Modeling of Pitting of Al and Al/Cu in Chloride Solution

Aluminum Metal (Al)

Passive Oxide Layer (Al2O3)

Solution (Na+, Cl-, H2O)

Solution with Constant Ion Concentration (C0)

Simple 3D Lattice-gas Model

Pits formed by continuous kinetic events (reaction + diffusion/migration)

),,( NeighborspHEfk appliedi =

Reaction rate calculation

−=

RTEkr i

ii exp ),( 0, NeighborsEfE ii =

Model SystemModel System : Aluminum-copper alloy in aqueous Aluminum-copper alloy in aqueous NaClNaCl solution environment solution environment

Reactions Considered

Metal ion hydrolysisMetal ion hydrolysis

Breakdown of oxide layerBreakdown of oxide layer Cl- + Oxidexide Cl- + Emptympty

Anodic dissolutionAnodic dissolution

k1

k7

(1)

Oxide Formation Oxide Formation 2Al + 3H2O Al2O3 (Oxidexide) + 6H+ + 6e–k18k19

(18,19)

(13,14)

(11,12)

Al3+ + H2O Al(OH)2+ + H+k5k6

(5,6)

Al Al3+ + 3e–k2 (2)

Al(OH)2+ + Cl- Al(OH)Cl+

Al(OH)Cl+ + H2O Al(OH)2Cl + H+

Al3+ + 3H2O Al(OH)3 + 3H+

Al3+ + 3Cl- AlCl3

k11

k9

k8

k10

k12k13k14

(7,8)

(9,10)

Water DissociationWater Dissociation

Water ReductionWater Reduction

H+ + OH- H2O

2H2O + 2e- H2 (g) + 2OH-

k16k17

(16,17)

(15)k15

Cu Cu2+ + 2e–k3 (3,4)k4

Note: WAGs for rate constants in some cases

KMC Modeling of Localized Corrosion of Pure Al in Aqueous Chloride SolutionKMC Modeling of Localized Corrosion of Pure Al in Aqueous Chloride Solution

Initial configuration

Evolution of pitEvolution of pit

LegendAlAl2O3

EmptyCl-

Al3+

H2O

LegendNa+

Al(OH)2+OH-

Effect of Copper Content and Configuration on Pitting Process of

Al and Al-Cu

• Three configurations:– randomly distribution– a 3x3 column of Cu– a cluster of 6-12 Cu atoms

Effect of Copper Content and Configuration

Al-Cu alloy layer Cu distribution

Effect of Cu on Nanopit Morphology

0 20 40 60 80 100 1200.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5r/h

Time (s)

Pure Al

Al-2Cu

Al-4Cu

Dish-like

Tunnel

Hemisphere

Effect of Cu on Pit pH

0 20 40 60 80 100 1201.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

pH

Time(s)

Pure Al

Al-2Cu

Al-4Cu

C=O

Pt-O2.5 Å

C= +1 e

Pt-O2.9 Å

C=-1e

Pt-O2.2 Å

DFT Calculations of Effect of Applied Potentialon Structure of Interfacial Water

• reorientation of the water molecules at the interface• oxidative adsorption of water on Pt upon electron depletion

Increasing potential across interface

Applied Science Issues for Lap Joint

• How often must a joint be exposed to waterto remain wet?

• Does prior corrosion affect kinetics ofwetting and drying?

• How does corrosion rate change duringwetting and drying?

• Can CPC enter lap joints? How long mustthe pool be at mouth?

LP01, co

Long Period Grating LP0n, cl

LP0n, cl

Core

Cladding

Affinity Coating

Long Period Grating Chemical Sensor

Wavelength (nm)

Index = 1.4215Index = 1.4230Index = 1.4245Index = 1.4260

Tran

smis

sion

(dB

)

Shift in Spectral Loss Wavelength withRefractive Index Changes

Environment ofInterest

Long Period Grating SensingMethodology

Concurrent Moisture/Corrosion Activity

0 1 2 3 4 5

Wav

elen

gth,

nm

14901540

1550

1560

1570

Time, days0 1 2 3 4 5

SIM

A, n

T-m

m2

0

200

400

600

800

0.1 M NaCl

Dry N2

Dry Condition

Dry Condition

SQUID

MOISTURE

Global measureof corrosionactivity

Measure ofmoisture within lap

SIMA = spatially integratedmagnetic activity

VanderbiltVanderbiltUniversityUniversity

VanderbiltVanderbiltUniversityUniversity

K. Cooper

Y-P Ma, J. P. Wikswo

#1 #2 #3 #4Sensorposition

Mouth

Rivet

hole

Rapid IngressCorresponds to Increasein Corrosion Rate

Time, hours-3 0 3 6 9 12 15

Wav

elen

gth,

nm

1485149014951540

1545

1550

1555

1560

1565

1570

1575LJ#1-1 (Ch#1)LJ#1-2 (Ch#2)LJ#1-4 (Ch#4)ImmerseDrainFibers - Dry

Immerse lap jointin 0.1 M NaCl

Dry Condition

Time, hours-3 0 3 6 9 12 15

SIM

A, n

T-m

m2

0

100

200

300

400

500

600

700

800LJ #1ImmerseDrainSQUID - Dry

Dry Condition

Time, hours12 24 36 48

Wav

elen

gth,

nm

1485149014951540

1545

1550

1555

1560LJ#1-1 (Ch#1)LJ#1-2 (Ch#2)LJ#1-4 (Ch#4)ImmerseDrainFibers - Dry

Time, hours12 24 36 48

SIM

A, n

T-m

m2

0

100

200

300

400

500

600

700

800LJ #1ImmerseDrainSQUID - Dry

0.1 M NaCl

Drain solution,introduce dry N2 gas

Dry Condition

Dry Condition

Slow MoistureEgress Correspondsto ContinuedElevated CorrosionRate

#1 #2 #3 #4Sensorposition

Mouth

Rivet

hole

Moisture and Corrosion in Lap JointsSummary

• How often must a joint be exposed to water to remain wet?– Pristine ~ 2 day, Corroded ~ 5 days

• Does prior corrosion affect kinetics of wetting and drying?– Corroded – wet faster, dry slower

• How does corrosion rate change during wetting and drying?– Corrosion rate inside lap joint increases on immersion in salt

solution, transient increase during drying

Modeling to Provide DesignGuidance for Coatings

Alclad 3003-H14. Exposed to flowing seawater for 22 months

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.001 0.01 0.1 1 10Current Density (A/m2)

Pote

ntia

l (V)

vs

SCE

[Cl- ]

idl

-2-1.8-1.6-1.4-1.2

-1-0.8-0.6-0.4-0.2

0.001 0.01 0.1 1 10Current Density (A/m2)

Pote

ntia

l (V)

vs

SCE

ipass (Alclad)

HER

Sample GeometryJ=0 (symmetry)

2S

2 cm

J=0.01 cm

J = Electric Flux

Figure not to scale

Aluminum Clad

AA 2024 T3

Sample GeometryJ=0 (symmetry)

2S

2 cm

J=0.01 cm

2S

2 cm

J=0.01 cm

J = Electric Flux

Figure not to scale

Aluminum Clad

AA 2024 T3

FEM Analysis ofPotential and CurrentDistribution in ThinElectrolytes

Metallic Coatings:Francisco Presuel-Moreno

2024

Alclad

Effect of Scratch Size

-1.8

-1.5

-1.2

-0.9

-0.6

-0.3

0

0 0.002 0.004 0.006 0.008 0.01

Distance (m)

Pote

ntia

l (V)

vs

SCE

500150025005000

[Cl]=0.005 M

ScratchWidth

µm

Ep(Clad)

Sharp Transition in Loss ofProtection

0

20

40

60

80

100

0 1000 2000 3000 4000 5000Scratch Size (µm)

%A

rea

Prot

ecte

d

Dotted linesindicatetransition

ipass maxidl minfor [Cl-] = 0.005 M

Base

ipass minidl max

ipass maxidl minfor [Cl-] >= 0.05 M

More Protection in High [Cl-] Due toBetter Throwing Power

0

1000

2000

3000

4000

5000

0.01 0.1 1

Pro

tect

ed S

crat

ch S

ize

(µm

)

[Cl]=0.005 M[Cl]>=0.05 M

Alclad ipass (A/m2)

5 0.5 0.05 idl AA2024 (A/m2)

Conclusions

• Engineering policy needs are helpful infocusing applied and fundamental sciencestudies without bastardizing them

• Fundamentals are required to define criticalquestions and to assist in design of newmitigation strategies

• Corrosion’s complexities hold manysurprises for fundamental thinking

AcknowledgementsCo-conspirators

• John Scully• Matt Neurock• Rudy Buchheit• Ray Taylor• Hongwei Wang• Francisco Presuel-Moreno• Donghai Mei• Kevin Cooper• Karen Ferrer• Keith Furrow• APES, Inc.

Funding Agencies• NSF (B. Macdonald)• NASA (R. Piascik)• AFRL (S&KT, NCI)

– Deb Peeler– Dick Kinzie– Don Neiser

• AFOSR (P. Trulove)• DOE

– Center for Synthesis &Processing (K. Zavadil)