1. Mapping Erosion-Corrosion of Composite WC/Co-Cr Based Coating
Tarek M. Abd El-Badia
PhD Student
Tribology Group
Mechanical Engineering Department,
University Of Strathclyde
Under supervision
Professor M. Stack

2. Outline Objectives of the study Experimental Work.
Results and Discussion.
Conclusions.
Future Work.
Acknowledgement.

3. 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).

4. Experimental work The slurry impingement erosion test rig:
The test rig is constructed (based on the design of Zu and Hutchings design)

5. Electrochemical slurry cell test

6. A Computer
Monitor
ACM (GILLAC)
POTENTIOSTAT A V AE WE RE

7. Testing conditions: Impact velocity: 3 m s-1. Impact angle: 90o
Electrolyte: Artificial sea water (according to ASTM D ).
Erodent particles: silica sand with average size 50mm to 250mm.
Applied potentials: 500, 250, 0 and-600 mV.
Slurry concentrations: 4%, 6%, 8% by wt%.
Erosion-corrosion wastage rate is determined by weight loss measurement
Corrosion contribution is determined by Faraday’s law.

8. Polarization curves
Mild Steel Substrate
WC/Co-Cr Coating

9. Erosion-Corrosion Wastage Definition
The wastage was defined as follows:
Kec= Keo + Kco + DKe + DKc
Ke= Keo + DKe
Kc= Kco + DKc
Kec…erosion- corrosion rate
Keo …erosion rate in absence of corrosion,
Kco… corrosion rate in absence of erosion.
DKe… effect of corrosion on erosion rate (synergistic effect)
DKc… effect of erosion on the corrosion rate (additive effect).

10. Mass loss for WC/Co-Cr coating at various applied potentials.
a) wt%= 4%.
(b) wt%=6%.
(c) wt%=8%

11. Mass loss for Mild Steel Substrate at various applied potentials.
a) wt%= 4%.
(b) wt%=6%.
(c) wt%=8%

12. Erosion-corrosion mechanism maps
Erosion-corrosion regimes can be defined as:
Corrosion
Corrosion-Erosion
Erosion- Corrosion
Erosion
Erosion-corrosion mechanism maps for Mild Steel Substrate
Erosion-corrosion mechanism maps for WC/Co-Cr coating

13. SEM analysis of WC/Co-Cr specimens
WC at C%= 8% and E=250mv
WC at C%= 8% and E=0mv
WC at C%= 8% and E=500 mv

14. SEM analysis of Mild Steel specimens
Mild steel at C%= 8% and E= 0mv
Mild steel at C%= 8% and E=-600mv
Mild steel at C%= 8% and E=250mv
Mild steel at C%= 8% and E=500mv

15. Erosion-corrosion wastage maps
low
Medium
High
Erosion-corrosion wastage map
for Mild Steel Substrate
Erosion-corrosion wastage map
for WC/Co-Cr coating

16. Erosion-corrosion synergism map
Low synergistic
Medium synergistic
High synergistic
Erosion-corrosion synergism map
for Mild Steel Substrate
Erosion-corrosion synergism map
for WC/Co-Cr Coating
N.B: Negative synergism is called antagonism

17. Erosion-corrosion additive synergism map
DKe/DKc < Additive
0.1<DKe/DKc < Additive-Synergistic
DKe/DKc > Synergistic
Erosion-corrosion additive synergism map for Mild Steel Substrate
Erosion-corrosion additive synergism map for WC/Co-Cr Coating

18. Conclusion
Erosion-corrosion mechanism maps, wastage, synergism maps have been developed for coating and substrate metals at range of particles concentrations showing the difference between the regimes.
The concentration of particles and applied potential can have a significant effect on the erosion-corrosion regime for the coating and substrate.

19. 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.

20. Acknowledgements
Professor M. Stack for great help and her useful Discussions in Tribo-corrosion Field.
Dr Stuart Lyon, Corrosion and Protection Centre, UMIST.
Workshop technicians and Tribology Group members in the Department of Mechanical Engineering, Univ. of Strathclyde, Glasgow.