hard AlSi-graphite abradable coating

[fhyuan]

I have tried to spray AlSi-graphite abradable coating (Metco 313NS) for quiete a long time. However, the coating mostly was hard (HR15Y nearly 80). Can anyone offer an advice for me to reduce the hardness?

Thanks

[Gordon]

Hi fhyuan

First, before you get too concern with your spraying procedure you need to make sure that your hardness testing results are in fact giving correct readings. Things like ensuring you have a minimum of 2 mm coating thickness for hardness testing and that surface preparation is not smearing/compressing the coating.

Metco 313NS tech bulletin gives typical macrohardness of 55 -80 HR15Y. Your readings appear at the top end and I would not worry too much as long as your readings are not going too far over the 80 mark.

[fhyuan]

Thanks, Gordon
I have the Metco 313NS tech bulletin. However the bulletin says that the AlSi-graphite is a kind of composite powder, but our OM microscope gave the blended powder photo. The blended powder consists of granular AlSi particles and flake like graphite. The blended graphite flakes imposes challenge for us to deposit a coating with acceptable hardness and uniform microstructure without massive porosity.

[Gordon]

Hi fhyuan

Not sure I really understand. Metco 313NS should contain composite particles bound together with an organic binder. There probably will be some free graphite particles, but the majority should be bound up. Are you using Metco 313NS or an alternative powder? To be honest, following the Metco parameters should not give you problems. Are you using all the specified equipment/parameters/powder?

[fhyuan]

Hi, Gordon:

The Metco 313NS is Al 5.5Si 45.5Graphite in composition. It does not have organic binder. We have tried the Metco 313NS and Metco 601NS using the specified equipment (PT A2000) with recommended parameters. However, we still had to test by ourselves on the powders since the recommended parameters did not produce acceptable coatings.

[Gordon]

Hi fhyuan

Unless I'm unaware of changes to this product specification, Metco 313 NS is an aluminium alloy - graphite composite powder.

Typical composition:
Aluminium 40%
Silicon 5.5%
Graphite 45%
Organic Binder 9%
(from Metco tech bulletin)

This product was originally designed for use with 7/9MB Metco guns. It sounds like you are going to need to do some process parameter development/optimisation work. I would be inclined to ask Sulzer Metco for some assistance. particularly if you are a good customer and considering the equipment and powder now comes under them. You should be able to do what it says on the tin so to speak