Hello,

I have several questions with difficulties to find right answers.

What is the typical microhardness (HV0.1) of Tantalum coating sprayed in VPS ?

Does anyone know a supplier for Tantalum powder (except HC Starck) ?

Does anyone know if Wc-10Co-4CR can be safely applied on Aluminum-Lithium alloys ??

Thank you for your help !

Hi TintinMilou

Quote:What is the typical microhardness (HV0.1) of Tantalum coating sprayed in VPS ?

About 650 HV/0.3 for APS (Metco62), sorry no info on VPS.

Quote:Does anyone know a supplier for Tantalum powder (except HC Starck) ?

If you reqire a fair quantity, it may be worth checking out ESPI http://www.espimetals.com, Cabot http://www.cabot-corp.com, READE http://www.reade.com but chances are will not have a product suitable for thermal spray off the shelf. If your required quantity is small, you may have little choice but to get it through a thermal spray powder supplier, high price but at least it should be suitable for spraying.

Quote:Does anyone know if Wc-10Co-4CR can be safely applied on Aluminum-Lithium alloys ??

I don't know of a reason why not. What is your specific concern?

Quote:Does anyone know if Wc-10Co-4CR can be safely applied on Aluminum-Lithium alloys ??

I don't know of a reason why not. What is your specific concern?
[/quote]

differences between coefficient of thermal expansion, substrate temperature during spraying...
I don't think there is a big issue since the part won't operate in high temperatures, but just wanted to make sure there is no uncompatibility.

Thanks for your quick answers.

Hi TintinMilou

I think conditions would be similar to aluminium and its other alloy substrates. Just be careful with process temperatures and try to keep coating thickness to a minimum.

Hi !

What do you mean by "minimum" ?

Hi TintinMilou

Basically, thinner coatings will be more durable (with respect to coating stresses) than thicker coatings. If your application allows, tend towards thinner coatings, rather than thicker and stay well within the coatings recommended thickness limitation.

Hello,

Regarding the application of WcCoCr coating by HVOF on ALuminum alloy substrate, I have been told that it could be a problem with 2 issues:
1/ surface oxidation after grit blasting since aluminium creates a superficial oxide layer very quickly.
2/ expansion properties are different and could cause spalling of the coating.

What do you think ? Is there a maximum substrate temperature we should not reach (below the melting point I mean...)

Thank you !

Hi TintinMilou

It is true that aluminium readily forms a thin oxide film and is the main reason this reactive metal is so corrosion resistant. Also the expansion properties are quite different. If the part is not going to see any dramatic temperature changes and is sprayed carefully, I don't think there should be a problem.

With aluminium substrates grit blasting should be at lower pressures to avoid grit entrapment. Preheating should be done indirectly (from the back or side, but not on the surface to be coated) to reduce the formation of surface oxides. Max preheat temperature ~90 C (cooler than for steels). Care should be taken to control coating/substrate temperature during spraying, try and keep temperature constant and not too far above your preheat temperature, say 150 C max. Poor temperature control could well cause the problems you describe through oxide formation and differential expansion.