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

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

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

Electrochemical slurry cell test

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

Testing conditions: Impact velocity: 3 m s-1. Impact angle: 90o Electrolyte: Artificial sea water (according to ASTM D 1141-98). 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.

Polarization curves Mild Steel Substrate WC/Co-Cr Coating

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).

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 Substrate at various applied potentials. a) wt%= 4%. (b) wt%=6%. (c) wt%=8%

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

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

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

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

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

Erosion-corrosion additive synergism map DKe/DKc < 0.1 Additive 0.1<DKe/DKc < 1 Additive-Synergistic DKe/DKc > 1 Synergistic Erosion-corrosion additive synergism map for Mild Steel Substrate Erosion-corrosion additive synergism map for WC/Co-Cr Coating

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.

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.

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.