Coating surface roughness

[William]

Hi all,
I want to know surface roughness for the every coating. Can anyone offer some information?
Thanks,
Best regards,

William

[Alexangel1226]

William,

I am afraid no one can give a an exact answer on your answer. The surface roughness your talking about is it Ra, Rz, Rmax....etc and it depends on the application , industries and the customers' needs.

Most of the coating has not surface roughness finishing requirement, for example in aviation, marine, indurstial, automobile...etc, we apply coating for wear resisitence, or dimension restoration, and all these doesnot requirement Ra on the coating finishing, as the coating will be machined down to dimension specified based on enghine manual or its seviceable limits.

For TBC coating also, Surface roughness is also not a critical variable to determine the coating is good or not, the metallorgraphic test, bend test, tensile, hardness tests, will be crucial for most of the coating.

Again coating families can be devided to many many types, dependon which you are applying. Eg: Abradable, metallic, Ceramic(oxide based), carbide based, .....which coating type your are refering to?

Yet, some coating on certain part do have the surface Ra requiremen tafter coating, like in semiconductor industries, the apply coatings Aluminum or others on the kits/parts, that require a min Ra. some as high as 35 mirco meter(um), they need the extremely coarse surface roughness to capture the particles in their CVD or PVD processes. In this case the metallorgraphic or the coating is not important, but Roughness and tensile. ...

In short, again, if you would like to know in more,you have to specify your needs, applications, coating types, industries used....then I believe more people would then like to share some lights here..

thanks and regards,
Alex

[Gordon]

Hi William

Surface engineering can produce surfaces with a vast range of "roughness" or surface finish. If you are talking thermal spray coatings, again the range is vast from mirror finished HVOF tunsten carbide coatings to extremely rough and textured arc spray coatings. I think you will need to be very much more specific about the information you require.

[drramc]

Hi,
As pointed out by Gordon, the coated surfaces may display a wide range of surface roughness values.However the post-spray or -coating processes, such as, grinding, polishing, honning, lapping etc are used to produce required surface finish.Designer need to specify both the level of finish and the type of finishing operation (see tab1.5 Roughness values of engineered surfaces,p24*)
For example the bore of an automobile engine cylinder needs Ra of 0.32micron, with a circumferential(ground) or angular (honed) lay,Any rougher surface leads to excessive wear, while smoother surfaces may cause improper sitting of piston ring, poor lubrication and thus eventually siezure(p23).
Surface roughness plays an important role in enhancing wear and fatigue resistance.
*in my book,'Surface Wear,Analysis, Treatment & Prvention,ASM Intl,20001, a full section devoted to surface roughness)

[dhermanson]

OK let me ask a similar questioin another way.??I am comparing two anti erosion coatings on the leading edge of our Stage 0 gas turbine low pressure compressor section.??One coating is a multi-layered metallic and ceramic matrix comprised of Titanium Nitride and other elements.??The other coating is chrome carbide.??The underlying blades are made of high strength corrosion resistant A-286 material. I intend to have a "rainbow rotor" of alternating coatings (if the rotor balancing allows).

What I would like to have is a test that would measure the change in surface roughness and leading edge roughness over time, but not harm the blades.??A subjective "feels like this grade of sandpaper" is not accurate enough to quantitatively share with the vendors.

Thank you

[hwang]

dhermanson Wrote:OK let me ask a similar questioin another way.??I am comparing two anti erosion coatings on the leading edge of our Stage 0 gas turbine low pressure compressor section.??One coating is a multi-layered metallic and ceramic matrix comprised of Titanium Nitride and other elements.??The other coating is chrome carbide.??The underlying blades are made of high strength corrosion resistant A-286 material.??I intend to have a "rainbow rotor" of alternating coatings (if the rotor balancing allows).

What I would like to have is a test that would measure the change in surface roughness and leading edge roughness over time, but not harm the blades.??A subjective "feels like this grade of sandpaper" is not accurate enough to quantitatively share with the vendors.

Thank you

------------------
Hi,
How about doing surface replica whenever and wherever you like on the blade and take measurement afterwards on the replica...

Hong Wei Wang, ERA Technology, UK

[Gordon]

Hi dhermanson

to the Surface Engineering Forum.

hwang Wrote:

dhermanson Wrote:OK let me ask a similar questioin another way. I am comparing two anti erosion coatings on the leading edge of our Stage 0 gas turbine low pressure compressor section. One coating is a multi-layered metallic and ceramic matrix comprised of Titanium Nitride and other elements. The other coating is chrome carbide. The underlying blades are made of high strength corrosion resistant A-286 material. I intend to have a "rainbow rotor" of alternating coatings (if the rotor balancing allows).

What I would like to have is a test that would measure the change in surface roughness and leading edge roughness over time, but not harm the blades. A subjective "feels like this grade of sandpaper" is not accurate enough to quantitatively share with the vendors.

Thank you

------------------
Hi,
How about doing surface replica whenever and wherever you like on the blade and take measurement afterwards on the replica...

Hong Wei Wang, ERA Technology, UK

There are various portable roughness or surface profile measurement devices that will give direct Ra readings with the option of using a graphical printer for more detailed information. I do like very much hwang's suggestion of using physical surface replica though.

[drramc]

Surface roughness can be measured by contact methods (Stylus instrument,frictional dynamometer, thetameter,thermal comparator,electrical methods etc) or Optical methods( optical probes using laser or infra red beams)For microscale roughness measurementuse non-contact Confocal Scanning Optical Microscope(SOM0),to obtain 3-dimensional surface morphology.
Please refer to section on 'Surface Roughness' of my first book for further information.Depending on the roughness of the surface you can use an appropriate non-contact optical gauge, with complete edge roughness tracking system hooked to a computor.
ram chattopadhyay