crack grows incrementally typ. 1 to 6 increase in crack length per loading cycle failed rotating...

• Crack grows incrementallytyp. 1 to 6

a~

increase in crack length per loading cycle

• Failed rotating shaft --crack grew even though

Kmax < Kc

--crack grows faster as • increases • crack gets longer • loading freq. increases.

crack origin

Fatigue MechanismFatigue Mechanism

mKdN

da

• Fatigue limit, Sfat:

--no fatigue if S < Sfat

Adapted from Fig. 8.19(a), Callister 7e.

Fatigue Design ParametersFatigue Design Parameters

Sfat

case for steel (typ.)

N = Cycles to failure103 105 107 109

unsafe

safe

S = stress amplitude

• Sometimes, the fatigue limit is zero!

Adapted from Fig. 8.19(b), Callister 7e.

case for Al (typ.)

N = Cycles to failure103 105 107 109

unsafe

safe


Improving Fatigue LifeImproving Fatigue Life1. Impose a compressive surface stress (to suppress surface cracks from growing)

N = Cycles to failure

moderate tensile mLarger tensile m


near zero or compressive mIncreasing

m

--Method 1: shot peening

put surface

into compression

shot--Method 2: carburizing

C-rich gas

2. Remove stress concentrators. Adapted from

Fig. 8.25, Callister 7e.

bad

bad

better

better

Adapted fromFig. 8.24, Callister 7e.

• Corrosion: -- the destructive electrochemical attack of a material. -- Al Capone's ship, Sapona, off the coast of Bimini.

• Cost: -- 4 to 5% of the Gross National Product (GNP)* -- this amounts to just over $400 billion/yr**

* H.H. Uhlig and W.R. Revie, Corrosion and Corrosion Control: An Introduction to Corrosion Science and Engineering, 3rd ed., John Wiley and Sons, Inc., 1985.**Economic Report of the President (1998).

Photos courtesy L.M. Maestas, Sandia National Labs. Used with permission.

THE COST OF CORROSIONTHE COST OF CORROSION

What is CORROSION?What is CORROSION?

Corrosion is a natural event It represents a return of metals to their more natural state as minerals (oxides)

Metal “Wants” to be DirtMetal “Wants” to be Dirt

ENERGY

METALORE

Basics of CorrosionBasics of Corrosion

Corrosion is essentially the oxidation of metal

Need:1. An Anode (where oxidation is taking place)2. A Cathode (where reduction is taking place)3. Conductive electrolyte4. Electrical contact between the Anode and Cathode

Source: Moore, J.J. Chemical Metallurgy

ElectrochemistryElectrochemistry

Corrosion is an electrochemical reactionCorrosion is an electrochemical reaction– ½ reaction at the anode½ reaction at the anode:: M MM Mn+n+ + ne- + ne-

– Possible ½ reactions at the cathode:Possible ½ reactions at the cathode: 2H2H++ + 2e + 2e-- H H22

Acid Solutions:Acid Solutions: H H22O + eO + e-- ½ H ½ H22 + OH + OH--

½ O½ O22 + 2H + 2H++ + 2e + 2e-- 2OH 2OH--

Important thing to note is the flow of electronsImportant thing to note is the flow of electrons

Thermodynamic Driving ForceThermodynamic Driving Force

Like all chemical reactions – ThermodynamicsLike all chemical reactions – Thermodynamics What is the driving force for the reaction? What is the driving force for the reaction?

(otherwise stated as what is the electrochemical (otherwise stated as what is the electrochemical potential for the reaction)potential for the reaction)– Dissimilar metalsDissimilar metals– Different cold work statesDifferent cold work states– Different grain sizesDifferent grain sizes– Difference in local chemistryDifference in local chemistry– Difference in the availability of species for a reaction Difference in the availability of species for a reaction

(concentration cells)(concentration cells)– Differential aeration cellsDifferential aeration cells

Derivation of Nernst EquationDerivation of Nernst Equation

eFeFe 22

tsreac

productsoo

a

aRTGQRTGG

tan

ln)ln(

)(22 2 gHeH

For:

)(2 22 gHFeHFe

2

2

22

2

][

][ln

)()(

)()(ln

H

FeG

HaFea

HfFeaGG oo

1

1

Derivation of Nernst Equation…Derivation of Nernst Equation… Introduce: The total electropotential isIntroduce: The total electropotential is

G = -nFEG = -nFEWhere:Where:

F = Faraday’s constant (total charge on Avogadro’s number of electrons)F = Faraday’s constant (total charge on Avogadro’s number of electrons)n = the number of electrons transferredn = the number of electrons transferredE = The electrode potentialE = The electrode potential

)ln(

)ln(

QRTnFEnFE

or

QRTnFEnFE

o

o

Thermodynamics ContinuedThermodynamics ContinuedNernst Equation:Nernst Equation:

THE BasicTHE Basic equation which describes equation which describes ALLALL corrosion reactions corrosion reactions

)ln(QnF

RTEE o

For Our Example:

2

2

][

][ln

H

Fe

nF

RTEE o

Note: pH = -log10[H+]

Pourbaix DiagramPourbaix Diagram

Potential vs pHPotential vs pH pH is the measure pH is the measure

of [Hof [H++] ions in ] ions in solutionsolution

Map regions of Map regions of thermodynamic thermodynamic stability for stability for metal’s aqueous metal’s aqueous chemical specieschemical species

Source: www.corrosionsource.com

STANDARD EMF SERIESSTANDARD EMF SERIES• EMF series

AuCuPbSnNiCoCdFeCrZnAlMgNaK

+1.420 V+0.340- 0.126- 0.136- 0.250- 0.277- 0.403- 0.440- 0.744- 0.763- 1.662- 2.363- 2.714- 2.924

metal Vmetalo

mor

e an

odic

mor

e ca

thod

ic

• Metal with smaller Vo

metal corrodes.

• Ex: Cd-Ni cell

V = 0.153V

o

-

1.0 M

Ni2+ solution

1.0 M

Cd2+ solution

+

25°C NiCd

Galvanic SeriesGalvanic SeriesHUNTINGTON CITY WATER, 25HUNTINGTON CITY WATER, 25CC

Volts: Saturated Calomel Half-Cell Reference Electrode

+0.

4

+0.

3

+0.

2

+0.

1 0

-0.1

-0.2

-0.3

-0.4

-0.5

-0.6

-0.7

-0.8

-0.9

-1.0

-1.1

-1.2

-1.3

-1.4

-1.5

-1.6

-1.7

-1.8

MagnesiumManganese

Cast IronZinc

AluminumAluminum Alloy 5052

Mild SteelTinLead

Nickel - SilverCopperAlloy 20Cb3Alloy 18-18-2Brass Alloys

Alloy 3RE6070 - 30 Copper-Nickel90 - 10 Copper-NickelAlloy EFE62

Bronze AlloysAlloy 6XAlloy 17-4PHAlloy 255 (ferrallium)Alloy 230 (Coronel)

Alloy 26-1, 26-1 - 1/4Alloys C276, G, X

Alloy 254 SLXMONEL alloys 400, R405, K500Alloy B, P, PD (Illium)INCOLOY alloy 800, 825, 840

Nickel 200, 270Stainless Steel 304, 316, 317, 403

INCONEL alloys 600, 617, 618, 625, 671, 690, 702, X750TitaniumAlloy 700 (Jessop)

+0.64 - 0.76V Platinum

Source: Crum and Scarberry, Corrosion of Nickel Base Alloys Conference Proceedings - ASM 1985

Kinetics Describes Rate of ReactionKinetics Describes Rate of ReactionEvan’s DiagramEvan’s Diagram

CORRE

CORRi

CURRENT DENSITY, A/cm²

BB

A

0

0

E

E

io Fe ANODIC

ANODIC

Fe F

e+2 +2e-

H 2H+ +2e-

2

PO

TE

NT

IAL

VO

LT

S (

SH

E)

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

10 10 10 10 10 10 10 10 10-10 -9 -8 -7 -6 -5 -4 -3 -2

CATHODIC

CATHODIC

Fe +2 +2e - Fe

2H + +2e - H2

A

for H2on Fe

io

Area EffectsArea Effects

M

M+ +

e-

iaO2

Ac

ioH+ Aa

½ O2 + H

2O + 2e - 2OH -

AaioO2

CreviceEffect

No CreviceEffect

PLUS CreviceEffect

icorr in very aggresive environment

Log

E

EM/M+

EO2 /OH +

= Area Inside Crevice (Anodic)= Area Outside Crevice (Cathodic)

Aa << Ac

Aa

Ac

i

+oi H Ac

Effect of Oxidizer Concentration (e.g., Oxygen) on the Effect of Oxidizer Concentration (e.g., Oxygen) on the Electrochemical Behavior of an Active - Passive MetalElectrochemical Behavior of an Active - Passive Metal

Log i

M M+

[Fontanna and Greene, Corrosion Engineering, McGraw-Hill, 1967]

Increasing OxidantConcentration

Effect of Effect of TemperatureTemperature and Dissolved O and Dissolved O22


Galvanic Series - Concentrated Hydrochloric Acid at 25°C [Crum and Scarberry, Corrosion of Nickel Base Alloys Conference Proceedings - ASM 1985]

+0.4 +0.3 +0.2 +0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 -1.0 -1.1 -1.2 -1.3 -1.4 -1.5 -1.6 -1.7 -1.8MagnesiumManganeseAluminumZincCadmiumLeadAlloy 255 (Ferralium)High Purity IronCopperAlloy PE 62Alloy 26-1, 26-1 1/4Carbon SteelMONEL alloy 451TinAlloy 18-18-2Alloy 3RE60Alloy 17-4pHINCOLOY alloy 840, 50 Ni - 50 CrBrass AlloysNickel Silver90-10 Copper-NickelBronze Alloys70-30 Copper-NickelAlloy 230 (Corronel)Alloy 70Cb3Stainless Steel 304, 316, 316L, 317Alloy 20Cast IronNi-Resist 2Alloy 254 SLXAlloy 904LINCONEL alloys 600, 601, 690, 702, 748, X750INCOLOY alloy 825Alloy B, P, PD (Illium)Alloy GAlloy 6X (HA)MONEL alloys 400, 404, 405R, K500Nickel 200, 270Alloy 700 (Jessop)Alloy 6XSilverAlloy GINCOLOY alloy 800INCONEL alloys 617, 618E, 625Aluminum Alloy 5052Stainless Steel 430Titanium+0.4-0.48V Platinum 92345r1

DISSOLVED O2 (Mg / H2O)

35

30

25

20

15

10

5

0

CO

RR

OS

ION

RA

TE (

MPY))

DISSOLVED O2 (PPM)0 1 2 3 4 5 6 7 8 9 10 11

0 0.7 1.4 2.1 2.8 3.5 4.2 4.9 5.6 6.3 7.0 7.7

LEGEND

FRESH WATER @ 50°FFRESH WATER @ 90°FFRESH WATER @ 120°FVELOCITY = 2.5 FPS

pH=7, R=100M-0HMpH=7, R=2500M-0HM

Types of Aqueous Corrosion CellsTypes of Aqueous Corrosion Cells

– General CorrosionGeneral Corrosion– Localized CorrosionLocalized Corrosion

PittingPittingCrevice CorrosionCrevice CorrosionUnder-deposit CorrosionUnder-deposit CorrosionMICMIC

– TuberculationTuberculation– Galvanic CorrosionGalvanic Corrosion

General CorrosionGeneral Corrosion


Random Creation and Destruction of Anodes and Cathodes

Movement of Anodes and Cathodes

Near Uniform Thinning Weight Loss is a Useful

Measure

O

O

M+

e

e

-

-

O

O

M+e

e

-

-

O

OH

M+

-

e

e

-

-

O

OH

M+

M+

-

e

e

e

-

-

-

Source: Corrosion, ASM Handbook, Volume 13, 1987


Original Surface

Penetration due to Corrosion

Localized CorrosionLocalized CorrosionCarbon SteelCarbon Steel

Localized CorrosionLocalized Corrosion Stationary ElectrodesStationary Electrodes All of the dissolution occurs All of the dissolution occurs

in one locationin one location Weight loss measurement – Weight loss measurement –

not usefulnot useful Local PenetrationLocal Penetration

– Sometimes local weakeningSometimes local weakening– May or may not jeopardize May or may not jeopardize

structural integritystructural integrity– Determines “failure”Determines “failure”




Mn+

CI-OH-M(OH)n M(OH)n

OH-

e e-

Source: Corrosion, ASM Handbook, Volume 13, 1987

Potential and Current Fields in Electrolyte in Potential and Current Fields in Electrolyte in the Vicinity of a Localized Corrosion Sitethe Vicinity of a Localized Corrosion Site




Pot

entia

l

Anodic+

- Localized Anodic Site

Metal

Cathodic

Cur

rent

Den

sity

crack grows incrementally typ. 1 to 6 increase in crack length per loading cycle failed rotating...

Documents

h slide

cost of corrosion slide

basics of corrosion

corrosion reactions

stress amplitude slide

o e h

electrochemistry corrosion

corrosion control