Mapping Erosion-Corrosion of Mapping Erosion-Corrosion of Composite WC/Co-Cr Based CoatingComposite WC/Co-Cr Based Coating

Tarek M. Abd El-BadiaPhD Student

Tribology GroupMechanical Engineering Department,

University Of StrathclydeUnder supervision Professor M. StackProfessor M. Stack

Outline Outline

• Objectives of the study

• Experimental Work.

• Results and Discussion.

• Conclusions.

• Future Work.

• Acknowledgement.

Objectives of the study Objectives of the study

1)Investigate the Erosion-Corrosion behaviour of WC/Co-Cr based coating through comparing with the mild steel substrate in sea water conditions.

2) Evaluate the mechanism of Erosion-Corrosion.

3) Construct the Erosion-corrosion maps for both materials ( uncoated and coated materials).

Experimental workExperimental work

The slurry impingement erosion test rig:

The test rig is constructed (based on the design of Zu and Hutchings design)

XInlet nozzle

Exit nozzle

Exit nozzle

Solution A.E

Potentiostat

W.ER.EEjector Body

Electrochemical slurry cell test Electrochemical slurry cell test

ACM (GILLAC) ACM (GILLAC) POTENTIOSTAT

A

V

AE

REWE

A ComputerA ComputerMonitorMonitor

Testing conditions:Testing conditions:• Impact velocity: 3 m s3 m s-1-1.• Impact angle: 9090oo

• Electrolyte: Artificial sea water (according to Artificial sea water (according to ASTM D 1141-98).ASTM D 1141-98).

• Erodent particles: silica sand with average size silica sand with average size 5050m m to 250to 250m.m.

• Applied potentials: 500, 250, 0 and-600 mV.500, 250, 0 and-600 mV.• Slurry concentrations: 4%, 6%, 8% by wt%.4%, 6%, 8% by wt%.• Erosion-corrosion wastage rate is determined by is determined by

weight loss measurementweight loss measurement• Corrosion contribution is determined by Faraday’s is determined by Faraday’s

law.law.

Polarization curves Polarization curves

WC/Co-Cr Coating Mild Steel Substrate

The wastage was defined as follows: Kec= Keo + Kco + Ke + Kc

Ke= Keo + Ke

Kc= Kco + Kc

Kec…erosion- corrosion rate

Keo …erosion rate in absence of corrosion,

Kco… corrosion rate in absence of erosion.

Ke… effect of corrosion on erosion rate (synergistic effect)

Kc… effect of erosion on the corrosion rate (additive effect).

Erosion-Corrosion Wastage DefinitionErosion-Corrosion Wastage Definition

• Mass loss for WC/Co-Cr coating at various applied potentials.

a) wt%= 4%. (b) wt%=6%.

(c) wt%=8%

• Mass loss for Mild Steel SubstrateMild Steel Substrate at various applied potentials.

(c) wt%=8%

a) wt%= 4%. (b) wt%=6%.

Erosion-corrosion mechanism maps Erosion-corrosion mechanism maps Erosion-corrosion regimes can be defined as:

10/

10/1

1/1.0

1.0/

cKeKcKeKcKeK

cKeK Corrosion Corrosion Corrosion-Erosion Corrosion-Erosion Erosion- CorrosionErosion- CorrosionErosionErosion

Erosion-corrosion mechanism maps for WC/Co-Cr coating

Erosion-corrosion mechanism maps for Mild Steel Substrate

SEM analysis of SEM analysis of WC/Co-Cr specimens WC/Co-Cr specimens

WC at C%= 8% and E=0mv WC at C%= 8% and E=250mv WC at C%= 8% and E=500 mv

Mild steel at C%= 8% and E=-600mv Mild steel at C%= 8% and E= 0mv

Mild steel at C%= 8% and E=250mv Mild steel at C%= 8% and E=500mv

SEM analysis of SEM analysis of Mild Steel specimens Mild Steel specimens

Erosion-corrosion wastage maps Erosion-corrosion wastage maps

21

2121

21

..50

..50..6

..6

cmhmgecK

cmhmgecKcmhmg

cmhmgecK low

Medium

High

Erosion-corrosion wastage map for WC/Co-Cr coating

Erosion-corrosion wastage map for Mild Steel Substrate

Erosion-corrosion synergism mapErosion-corrosion synergism map

10/

10/1

1/

ee

ee

ee

KK

KK

KK Low synergistic

Medium synergistic

High synergistic

Erosion-corrosion synergism map for WC/Co-Cr Coating

Erosion-corrosion synergism map for Mild Steel Substrate

N.B: Negative synergism is called antagonism

Ke/Ke/Kc Kc << 0.1 Additive 0.1 Additive

0.1<0.1<Ke/Ke/Kc Kc << 1 Additive-Synergistic 1 Additive-Synergistic

Ke/Ke/Kc > 1 SynergisticKc > 1 Synergistic

Erosion-corrosion additive synergism Erosion-corrosion additive synergism mapmap

Erosion-corrosion additive synergism map for WC/Co-Cr Coating

Erosion-corrosion additive synergism map for Mild Steel Substrate

Conclusion

• Erosion-corrosion mechanism maps, wastage, synergism Erosion-corrosion mechanism maps, wastage, synergism maps have been developed for coating and substrate maps have been developed for coating and substrate metals at range of particles concentrations showing the metals at range of particles concentrations showing the difference between the regimes.difference between the regimes.

• The concentration of particles and applied potential can The concentration of particles and applied potential can have a significant effect on the erosion-corrosion regime have a significant effect on the erosion-corrosion regime for the coating and substrate.for the coating and substrate.

Future work: 1) Construction of maps for velocity and the

particle concentration effects for coated and uncoated materials at various applied potentials.

2) Study the effect of volume fraction of carbide particles on the maps for various erosion conditions.

AcknowledgementsAcknowledgements

• Professor M. Stack for great help and her useful Professor M. Stack for great help and her useful Discussions in Tribo-corrosion Field.Discussions in Tribo-corrosion Field.

• Dr Stuart Lyon, Corrosion and Protection Centre, Dr Stuart Lyon, Corrosion and Protection Centre, UMIST.UMIST.

• Workshop technicians and Tribology Group Workshop technicians and Tribology Group members in the Department of Mechanical members in the Department of Mechanical Engineering, Univ. of Strathclyde, Glasgow.Engineering, Univ. of Strathclyde, Glasgow.