How to increase coating hardness

[Airbin]

Hi Gordon and Everyone,

I have read a lot of discussion in the forum and try to figure out the way to increase coating hardness. If I am wrong about something, please correct me.

1. Increase the power to increase temperature to melt the powder.
I have tried some tests to observe this. (1) When I sprayed Metco 450NS, I decreased the power and the hardness was a little lower. I need to decrease powder feed rate to increase the hardness. (2) When I sprayed Metco 308NS, I increased the acetylene to increase the powder, the coating was harder.

2. Decrease gas to increase oxidation.
When I sprayed Metco 68F-NS-1, the coating hardness was around R15N 76. When I turned off the secondary gas Helium, the hardness was around 81, but oxidation was also more.

3. Increase coating density.
I don’t really know how to increase coating density. May I increase carrier gas flow to increase coating density? Does the turn table speed affect the coating density?

4. Change gun to part distance.
I have tried to change the distance when I sprayed Metco 601NS. The hardness of distance 3 inch was better than 4 inch, and 5 inch is the lowest. Honestly, I don’t know why. Can anyone explain this?

5. Some other way to affect hardness???

Thank you.
Bin

[sreenuvundela]

Hi Bin,

You can increase hardness by using optimised process parameters only.
But you can try with fine powders which will increases density and hardness.

Kindly note that main powders in thermal spray are three types such as Metal & Alloys, Ceramics and Carbides. we can not generalize optimisation of process parameters because the mechanical and physical properties of the powders are different.

In general, fine powders, high RPM of the component (loose particles fly off), lesser coating thickness per pass and high powder particle velocities will increase density and hardness also.

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Hi Bin,

You can increase hardness by using optimised process parameters only.
But you can try with fine powders which will increases density and hardness.

Kindly note that main powders in thermal spray are three types such as Metal & Alloys, Ceramics and Carbides. we can not generalize optimisation of process parameters because the mechanical and physical properties of the powders are different.

In general, fine powders, high RPM of the component (loose particles fly off), lesser coating thickness per pass and high powder particle velocities will increase density and hardness also.

SREENU

[Airbin]

Hi SREENU,
Thanks for your reminding. Of course, by using optimised process parameters can increase hardness. But before we find the optimised parameters, I want to know the general ways to increase coating hardness. Sometimes I adjust some parameters to increase hardness, but I don't know why.
As you mentioned, high RPM or lesser coating thickness may increase coating density and hardness. I will try it next at next test for 68F-NS-1. About high powder particle velocity, may I setup higher primary gas flow to achieve it?

Bin