WC-12Co low hardness

[DanyGans]

Hello all,

I recently work on development of APS WC-12Co (DIAMALLOY 2004) coating according F50TF15 spec. The system is new and helium gas still not installed.
I've sprayed a few trails where the porosity level is fine V2 and bond strength results about 7000psi. Hardness Rockwell superficial requir. 83 R15N min.
After few trails cannot get more then 82-83.

Parameters used:
Gun:3MB
Nozzle:GHW
Port:#2
Ar/H2=80/11
Amps=500 (Volt=75; 42kw)

Carrier=10 lpm; p.rate=40 gr/min.
Carrier seems abit high, but necessary to center the powder into the torch.

Sp.Distance=4"
Gun Speed=7mm/sec

Guys, I need any ideas how to increase the hardness.

My first assumption was if I could decrease the porosity the hardness will increase.
I already made small DOE by increasing the amps to 600. Same surface hardness.
Sp.Distance 80mm and 130mm. Same results.
Feed rate 30 gr/min and 50 gr/min. Same results.
Argon 60 lpm. Same results.

I have assumption if the hardness is below minimum maybe carbide dissolution occur or decarbonization.

Thanks a lot for your professional advices!!!

[Gordon]

Hi DanyGans

Ideally Ar/He plasma gas should be used.

If you make some of the following changes to Ar/H2 parameters coating should improve hopefully or at least give better starting point parameters to work from.

This thread Thread-improving-72FNS-microstructure worth a read.

Parameters used:
Gun:3MB
Nozzle:GHW ****change to narrow bore GP nozzle type****
Port:#2 ****change to #3 or #5****
Ar/H2=80/11 ****dramatically increase primary argon ~160****
Amps=500 (Volt=75; 42kw) ****try to keep around 70-75V or maybe a bit lower****

Carrier=10 lpm; p.rate=40 gr/min. ****should higher than typical****
Carrier seems abit high, but necessary to center the powder into the torch.

Sp.Distance=4" ****change to 2.5 - 3.5"****

[loriolo]

Hi Dany
As it is well known, WcCo powders must be sprayed by HVOF, because is necessary a high particles speed, so to spray WcCo powders with plasma is necessary to use A/He gas in order to avoid H embrittlement, or only A, As you use a 3MB gun, it will be very difficult to reach a high velocity, the best would be a 7MB or 9MB, you can use the following parameters and only A, without H:
Spray distance 60 mm
Spray rate 38 gr/min
Nozzle GE / Argon 100 psi / flow 220
Powder port #5
Amp 500, volts 62

[DanyGans]

Thank you Gordon and Loriolo for your recommendations.
I will apply these on my process and try to improve the hardness.
Concurrently I have a capability to spray with high intensity plasma torch gun (cascade) to get more particles velocity.