Just imagine we are depositing aluminium over steel using hot dipping or TIG surfacing. Over this specimen can we use PEO technique to fabricate corrosion resistant coating?
Dear Mr Siva,
Yes it is possible. During EPO, the surface exposed to electrolyte is important.
Can explain me your application area in brief. You only want to develop a corrosion resistant coating/film only or wear resistance is alsi desirable. What thickness you want of your film on steel substrate??
Dear Lalit sir,
I want to make coating on steel to make it corrosion resistant. Thickness should be very low. PEO is a fast and environmental friendly procees. But we cannot apply this in the case of steel. That is why i need to know is it possible to apply PEO over aluminium deposited steel.
HOW MUCH THICKNESS YOU WANT ? if thickness is required in the range of 100-500 microns and you want to oxidized aluminum (i.e. Al2O3, alumina) then I think you can coat steel directly with Alumina powder using plasma or HVOF thermal spray processes.
Dear Siva
It is possible and you could find layers with thickness more than 10 micron in Al-dipped steel substrate. I have done it 4 to 5 years ago. but the problem is due to high porosity morphology of produced coatings, they would not present much more corrosion resistivity. For this purpose, you need to have overall at least 100 micron of thickness and/or could be filled the porosity with a corrosion-resistant top layer.
I hope my information could help you.
If you are comfortable with 80-100 micron then go for Vaccum plasma sprayed or HVOF sprayed alumina coating. You can get porosity even less than 1% or may be 0.5%.
HVOF is definitely a good process to get good coating. But due to plasma temperature, the substrate microstructure varies. However, in PEO there wont be any such variation in microstructure, as the process is submerged in electrolyte.
If we talk about steel substrate a temperature of 200°c which is maintained in thermal spray by compressed air blast will not cause any microstructural changes. Also the gun to substrate distance is is kept 300mm along with a trasverse speed of 1 m/s so that heat from plasma will not concentrate at any point and that's the beauty of thermal spray technology.
Mr.Lalith, the question raised by Mr.M.sivaprasad is feasibility of using PEO of Al coated steel. We should think abt usage of HVOF plasma on Al.
Mr. Siva ultimately wants a corrosion resistant coating less than 100micron thickness with least porosity. He is depositing Al coating by hot dip or tig surfacing and then oxidizing it to make corrosion resistant (Alumina) coating. I gave a suggestion to directly coat steel with Alumina based corrosion resistant coating by thermal spraying. This is my view and may or may not be acceptable to others.
Dear Lalit Sir,
Anyway we can't use PEO technique in steel. From your suggestions i came to know that we can use both HVOF and PEO technique on Al coated steel.
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