coating hardness corelation
01-17-2007, 06:26 PM,
Question  coating hardness corelation

Good evening.
Sorry for my bad English, first of all.
My question is about hardness determination of abradable coatings, for example Metco 307-NS, (75% Ni- 25% Graphite).
Actually we check it by Rockwell Superficial method, HR15Y scale. Alternative method is Hoffman Scratch measurement. Is it possible to build correlation between two these methods. Whether are standards for Hoffman Tester calibration available?

Thank you, volf
01-18-2007, 05:47 PM,
RE: coating hardness corelation
Hi volf

Sign0016 to the Surface Engineering Forum.

I've not used or evaluated the Hoffman Scratch method. I will make an assumption that this method could possibly be used on coated components non-destructively unlike HR-15-Y test (well I wouldn?t anyway). So if a good correlation between Hoffman and HR-15-Y tests could be established for your particular coating, then Hoffman scratch test results from components could be roughly related to HR-15-Y that you would get from your test pieces. Have I got the right idea of your post?

I would suspect that there is a correlation, but whether that will be accurate enough for practical use I?m not sure. I?ve not come across any published work on this. If you spray and test a lot of abradable coatings, I would build up a record of comparative hardness data. From this you should soon see if a reliable and practically useful correlation exists. Bear in mind that such a correlation if good, would probably only be valid for that specific coating type.

I?m hoping Alexangel1226 or any other SEF member with practical experience of Hoffman scratch testing will come along and comment.

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