Obtaining surface roughness requirement (and hardness > 1000 HV)

[vrakpant]

Hi Guys!

I need to obtain the surface roughness, Ra < 0,4 microns. The surface also must have a hardness > 1000 HV.

Anyone know a coating / surface modification I can use. Is it impossible to obtain the roughness with tecniques like diffusion,carbourization, nitration and/or bororonizing ?

Thanks for any reply!

Regards Ole

[Gordon]

Hi Ole

to the Surface Engineering Forum.

Well there are numerous treatments that could meet with your requirements, some requiring pre-grinding some post grinding.

Surface hardness and roughness alone is not much to go on as far as suggesting a suitable treatment. Application, base material, surface function, environment etc. are very important factors to consider.

[vrakpant]

(04-20-2010 02:11 AM)Gordon Wrote:  Hi Ole

to the Surface Engineering Forum.

Well there are numerous treatments that could meet with your requirements, some requiring pre-grinding some post grinding.

Surface hardness and roughness alone is not much to go on as far as suggesting a suitable treatment. Application, base material, surface function, environment etc. are very important factors to consider.

Thanks for your reply!

It's for the inner barrel in a telescopic joint exposed to marine atmosphere. It may be hard particles present and thats why i need the specified hardness. In order to seal the inner barrel external surface need to have a surface roughness (0,4 microns).

So i reckon plasma sprayed chrome oxide is not possible due to high porosity? and if i have to machine the surface (to get the roughenss) i'm afraid i will remove to much of the hardness!?

Do I have to obtain e.g hardness of 1800 in the beginning and then after removing 0.2 microns of the surface (to get the roughness) the hardness vil only be 1000 HV ?

regards

[Gordon]

Hi Ole

Quote:So i reckon plasma sprayed chrome oxide is not possible due to high porosity? and if i have to machine the surface (to get the roughenss) i'm afraid i will remove to much of the hardness!?

Do I have to obtain e.g hardness of 1800 in the beginning and then after removing 0.2 microns of the surface (to get the roughness) the hardness vil only be 1000 HV ?

All thermal spray coatings will have some degree of porosity. A good quality plasma sprayed chromium oxide coating (~ 1% porosity possible) should not stand out as having high porosity, when considered as a whole with plasma spray coatings. Thermal spray coatings are normally sealed where corrosion may be a problem.

Thermal spray coatings should maintain true hardness throughout the thickness of coating. You should apply the coating in a manner that will give the desired final thickness plus extra material to cover for loss in grinding and finishing.