strange ring shaped grooves in carbide coating

[DavidH]

We were doing some comparative inspection of carbide coatings from valves that were used for a qualification test. Originally we were focused on inspecting the images for apparent porosity, but when we looked at the images we saw some strange ring shaped features that appear to be shallow grooves. There are also some of these shallow looking grooves that are not so ring shaped. We do not believe these have caused any performance issues, however we are puzzled as to what is causing them. Does anyone have any experience or knowledge that might shed some light on these mystery rings.
Thanks
David H
   

[Vadim Verlotski]

We were doing some comparative inspection of carbide coatings from valves that were used for a qualification test. Originally we were focused on inspecting the images for apparent porosity, but when we looked at the images we saw some strange ring shaped features that appear to be shallow grooves. There are also some of these shallow looking grooves that are not so ring shaped. We do not believe these have caused any performance issues, however we are puzzled as to what is causing them. Does anyone have any experience or knowledge that might shed some light on these mystery rings.
Thanks
David H

This is simply remnants of water or alcohol on the cut surface. After polishing, the cut has to be dried with a hair dryer.

[Stephen Booth]

We were doing some comparative inspection of carbide coatings from valves that were used for a qualification test. Originally we were focused on inspecting the images for apparent porosity, but when we looked at the images we saw some strange ring shaped features that appear to be shallow grooves. There are also some of these shallow looking grooves that are not so ring shaped. We do not believe these have caused any performance issues, however we are puzzled as to what is causing them. Does anyone have any experience or knowledge that might shed some light on these mystery rings.
Thanks
David H

dear david, can you mark up your photo to show exactly which are the ringed grooves

[DavidH]

Stephen,
I have attached an image with the rings of interest circled in red to the original post. Thanks for the input that the rings might be residual fluid on the sample. I recall watching them take impressions from surfaces previously and they did used alcohol as cleaner before they took the impressions. I will check with the lab to see whether the sample got dried properly before the impressions of the surface were taken.
Thanks,
David H