coating Al cylinder for wear resistance

[sal]

Hi,
I want to replace the coating inside an Al cylinder by HVOF process.
the original coating has been Nicasil and I have tried Cr2O3 in Ni/Cr.
the coating cracks after 60 hours service. probably thermal expansion of coating and substrate is quite different. A bond coat will solve the problem or should i change the coating to for example stellite 6?
your help is appreciated.
Soltani

[loriolo]

Hi
There are not enough notices about the coating, like system used to perform the coating, I can assume, it was plasma spray, working temperatures, and so on, engine cylinder are usually coated with rotoplasma with very good performance, with APS system surely you need a bonding adeguate to the working temperatures.

[Stephen Booth]

Hi Soli

I know you are trying to be brief, but we really need more information, like:

Wear Resistance? What type of wear?
Part name, function?
Operating conditions?
Type of aluminium
Processed used, like loriolo says, is that Plasma on the original part
Coating thickness
Depth of the bore, diameter of the bore
Is it a blind cylinder, closed at one end?
etc etc......

[sal]

Hi Stephen and loriolo,
this cylinder is a vankel engine cylinder with internal diameter of about 30 cm oval shape. the height is about 7 cm and both sides open. the Al is a permanent mold casting one Al356 or Al357 (Al-Si Eutectic).
internal temp should be around 350 to 400 C.
the original coating is Nikasil with about 100 micron thickness and hardness around 500 HV.
I want to use HVOF system to replace the coating.
once I tries Cr2O3/Ni/Cr but coating cracks after 60 hours operation.
thanks,

Hi Soli

I know you are trying to be brief, but we really need more information, like:

Wear Resistance? What type of wear?
Part name, function?
Operating conditions?
Type of aluminium
Processed used, like loriolo says, is that Plasma on the original part
Coating thickness
Depth of the bore, diameter of the bore
Is it a blind cylinder, closed at one end?
etc etc......

[loriolo]

Hi soli
I mind that with a bond coat maybe your coating perform better, but the main problem will be the high temperature during spray on aluminum substrate, we performed many test both, with HVOF and Plasma, but the plasma spray coating performed better, for the HVOF test we needed to cool the piece with liquid nitrogen, so I recommend a plasma coating like the ones applied on engine cylinder

[djewell]

I would use CrC-75NiCr instead of CrO-NiCr. CrC is a much tougher coating.

[sal]

Thanks guys,
I have ordered CrC instead of CrO and will try and let you know if it woks better or not.
Soli

I would use CrC-75NiCr instead of CrO-NiCr. CrC is a much tougher coating.

[sal]

Dear djewell,
I forgot to thank you for recommending CrC for my application which I ordered, coated and test results were much better.
I have another question; working with a 15E GTV (similar to 16 E Metco) we get flash backs into the gun. could it be due to o-ring problem or gases pressure?
Regards,
Soli

I would use CrC-75NiCr instead of CrO-NiCr. CrC is a much tougher coating.