HELP - Coating Chemistry

I need to identify the chemical nature of a thin coating made on a small piece of high carbon steel. I have a very limitted access to technological tools.
How can I know what it is? Or, how could I discard some coating (in an elimination process)?
I know it is dark gray (almost black) and very hard. I don't know the process used; could be PVD or others (Carburizing, Nitrizing, Borodizing,...). The coating is very thin, somewhere between 0 to 30 micrometer. I'm telling that because the thickness of the portion not coated has no visible difference in thickness with the coated portion.
Thank you in advance,
Roger

If you really need to know what it is for sure, you're going to have to do *some* kind of analysis, unless you can find a way to get in touch with the manufacturer. I would recommend XPS, XRD, or analytical SEM to determine the composition, if you think it is a PVD coating, and there are certainly companies that will do this analysis for you, for a price.

If it is very hard maybe is TiALN (generally thickness is less than 6 micron) so you do not have only PVD coatings. Maybe it is CVD coatings with other coating on the top.
To check maybe the first thng is to do: SEM analysis in surface and cross-section (chech thickness and morphology) EDS analysis during SEM to analyse the chemical composition. With this you can try to guess the coating type and depostion technique used (sometimes dificult!).
Good luck
Vasco
Check my Forum:
PVD Coatings and Vacuum Technology - Research Forum http://groups.yahoo.com/group/PVD_coatings
International Forum about current problems and solutions in R&D thin films and coatings technology based in vacuum surface treatments (Surface Engineering, Industrial Coatings, Plasma Treatment,PVD and CVD coating technology) Moderator: Vasco Teixeira (Univ. Minho)
Vasco Teixeira http://vteixeira.com.sapo.pt/PVD_coatings.htm Posted at: http://www.groupsrv.com