Hardness manipulation

[TurbineRepair]

Hi Guys,

Are there any general ways of manipulating a specific coating's hardness using the plasma system through hardware or parameter changes? I have 3 similar parts all sprayed in the same week with the same batch of powder (450 NS) but with completely different hardnesses. A couple are too hard if anything and one is really soft. I just need to understand what they could have changed during the week to produce such different coatings. Could a switch from GH to G nozzle (we run Ag) midweek make a significant difference to the hardness? How about electrode wear. Clearly either of these changes would show a voltage drop... if you were looking.

Thanks,

Jim

[plasmajet1990]

(09-17-2008 01:26 PM)TurbineRepair Wrote:  Hi Guys,

Are there any general ways of manipulating a specific coating's hardness using the plasma system through hardware or parameter changes? I have 3 similar parts all sprayed in the same week with the same batch of powder (450 NS) but with completely different hardnesses. A couple are too hard if anything and one is really soft. I just need to understand what they could have changed during the week to produce such different coatings. Could a switch from GH to G nozzle (we run Ag) midweek make a significant difference to the hardness? How about electrode wear. Clearly either of these changes would show a voltage drop... if you were looking.

Thanks,

Jim

Hi Jim,

The GH nozzle is used for Ar , the G nozzle is used for N2 (Nitrogen).
If you use the G nozzle for Ar the voltage will drop under 50 V and the power of the plasma will also drop. So , you will obtain an other coating.
Usualy Metco 450 NS is sprayed with the GH nozzle using Ar + H2.

Ion

[Gordon]

Hi Jim

If we take Metco 450 (Ni/Al) and probably many metal based coatings, these factors may typically influence hardness:

* coating density/porosity - denser gives harder
* inter-particle cohesion higher gives harder
* hard oxide inclusions more some times gives harder
* particle metallurgical structure

So variations in spray parameters will obviously effect coating quality and hardness. Generally, I would think too much particle heating would lead to a slightly harder coating and the opposite for under heating, but to a greater degree.

Ion is right, G nozzle is design for nitrogen plasma, though it will work with argon (as does the GE nozzle), but will not give same conditions as GH. This is the probable cause of your problem. Nozzle/electrode wear will effect coating quality at some stage (probably plasma gun health as well if extreme).

[TurbineRepair]

Hi guys,

I don't think I phrased my query very well - it wasn't me that was spraying! I appreciate the difference between the G and GH nozzle - don't pretend to fully understand the physics but I appreciate their different forms will modify the plasma Personally, with our set up, I like run the standard parameters and check the voltage obtained is healthy when ever I come to use the system.
The problem was 2 similar parts sprayed with the same powder in the same week but very different coating hardness an thus in this instance, quality. From my own suspicions and from the advise above I believe this was caused by an unauthorized nozzle swap ie GH to G. I think it would be worth checking our cooling too though.
Needless to say the suspect part has been reworked.

Thanks,

Jim