Chrome plating replacement

[Andy_UK]

Hi everyone,
I have a question about chrome plate replacement, we use APS to spray NiCr powders, but in some cases when we need to achieve lowest possible porosity, we cannot get appropriate results. We are not after a great hardness, in fact as long as it is in the area of 50 HRC, we are fine. Can anyone suggest a material and parameters to achieve good results? is the HVOF the only option?
For reference we use SG-100 Praxair system with H2 and Ar gases.

[Met.Eng.]

APS has a certain capacity about porosity. For the sealing of pores can be implemented. (Loctite 290, metco seals, maybe praxair seals.ect) However, If you ask me the best result I say to u HVOF process.

[djewell]

HVAF would be a cheaper option than HVOF to achieve low porosity. It will be cheaper and easier to implement and cheaper to operate.

[Andy_UK]

Well, thank you for your inputs, we will try other methods, I thought to give APS a chance...
Just a note about seals, we now use Dichtole, how is it compared to Loctite?

[Simon Kim]

I vote on Metallurgy Eng.'s opinion.
In my experience, HVOF is best way to replace Chrome plating.
And I can got the good result by mixed powder, iron base high Cr alloy and carbide powder 10%.

Simon

[kschewe]

The proper way is use hvof. a good choice would be tafa 1343

[Gordon]

Andy_UK and kschewe

to the Surface Engineering Forum.

is the HVOF the only option?

While HVOF/HVAF should be the superior option, I wouldn't say the only option. It is difficult to comment on whether you can improve upon your coatings with APS, without knowing much more about your existing coatings, process and desired coating function. Though, I agree in most situations HVOF/HVAF will give better coatings, its not to say that your APS system can not be to tuned to give a more than adequate coatings for your application.

[loriolo]

Hi Andy
You can get a little better results, changing the torch SG100 with another that can spray with a higher gas velocity, or try with helium/Argon, because SG100 performance with H2/Argon it’s not so good , it work better with Helium, if this is enough, otherwise as well as the other member write, the best solution is HVOF, it depend of the result you are looking for.

[Harrison jess]

go for HVOF process it is cheap and also easy to use .

[Stephen Booth]

Chrome Replacement may or may not mean replacing the coating with a chrome like material. Depending on the application, remember to consider the following materials, processes, methods could be a replacement for an existing chrome plating:

Ceramic, especially chrome oxide
Tungsten Carbides
CrC-NiCr
Arc Spray materials

APS can be used, especially if this is already existing in your facility, use it, improve it.

However if you must spray CrCNiCr in very large volumes, then most like the best choice will be HVOF or like Mr. Jewel pointed out, HVAF

[JJStick]

Andy_UK,

In the applications we have been doing to replace Chrome, the biggest problem is eliminating coating porosity to prevent corrosive agents from penetrating the coating and attacking the substrate. We sprayed up a number of hydraulic rods used on a salt water dock. The chrome was pitted, and the rods were lasting only about a year or so, sometimes less. After coating with WC the rods are still in service with no sign of pitting or wear after about 6 months. Hardness is not that important but density is.

Hope that his helps,
JJStick