Erosion Test of an Abradable Coating

[baaddin]

Dear All,
We are spraying 60:40 Ni/Graphite over Metco 450NS via flame spraying. Top coat thickness is within .060-.070". As you know this powder combination is an abradable coating and there is an erosion test reqirement which I should verify and we couldn’t have managed so far. My question is about this requirement.
The erosion rate requirement is in terms of sec/mil (max 9 sec/mil) but, I am a little bit over that requirement (11 sec/mil). I suppose I can lower this value by decreasing hardness (Hardness checks 70 HR15Y). Is this correct?
*Erosion rate: time to deplete a specific amount of grit media/depth of erosion
Technical Info:
We’re using a 6P-II gun with a 6PT-II-1 extension module and spraying at an angle of 80 degrees. System consists of oxygen, acetylene and Argon as carrier gas.
I can not change pressure values due to possible risk of alterations at other coatings. Flow values are as follows (nlpm):
-Oxygen: 14
-Acetlyene: 14
-Argon: 3.5
Spray rate: 55 gr/sec
Would you please advice if I should increase the spray rate or change the flow values? Or any other ideas?
Thank you very much.

[Gordon]

Hi baaddin

to the Surface Engineering Forum.

Change oxygen and fuel gas flows equally. Decreasing flow will make coating softer. Keep all other parameters constant. A HR15Y hardness of around 50 should give you the desired result.

[KevinS]

Look for what I call spider webbing between the nickel in the microstructure. It is a good indication of your temperature and it greatly affects the erosivity. No spider webbing and you get a low erosivity value high spider webbing you get a high value. Drop the temperature until less spider webbing is present and then chech the erosivity value.

[baaddin]

Thank you all for the recommendations. I'm going to start the trials today and will share the results.
Regards,