Roughness and particle size

[hustzc]

Hi,every one ,
if anyone kown these questions?
1) If the particle finer uesing in the thermal spraying system, the more rough the final as-deposited coating?

2) ,if the more rough in the surface of coating after corrosion,the worse of its corrosion resistance?

Thanks for any help and answer.

[derek]

The finer powder you use, the smaller Ra you can get. not sure about the corrosion resistance.

[Gordon]

Hi Hustzc

Quote:1) If the particle finer uesing in the thermal spraying system, the more rough the final as-deposited coating?

As Derek says finer powders generally will produce a finer surface texture compared to coarser powders.

Quote:2) ,if the more rough in the surface of coating after corrosion,the worse of its corrosion resistance?

Not easy to generalise - coating? substrate? environment? sealed? Are we talking about corrosion of coating alone or its ability to protect substrate?

A rough coating may indicate more porosity than a fine coating, so you could consider that it will provide less corrosion protection to the coating/substrate in the unsealed condition.

You could consider a rough coating having deeper/larger nooks and crannies to retain dirt and moisture/ which may make conditions for corrosion more likely.

[hustzc]

Sorry, i think i didnot describe my question (2nd) clearly.
What i want to ask is that For as-polished A and B coating with initial Ra such as 1.025 um and 1.116 um respectively.
but after polarization corrosion, the Ra of A became to 1.519um and C was 1.498. Other corrosion condition was keepped the same (sealed well ) . If the corrosion resistance of A coating is worse than C coating ? duo to some reasons.

[MichiganMan]

Corrosion is primarily a surface phenomenon. Higher Ra indicates more exposed surface, which means more of the coating is in contact with the corrosive. Supposing that the environment is corrosive to the alloy that you have sprayed and ground, more metal will be able to react with the corrosive on a rougher surface and therefore the coating will corrode more quickly.