The indentation produced on the surface by the indenter in the attached image does not exhibit a square shape, and its diagonal lengths are unequal. It's worth noting that Vickers microhardness testing typically produces square-shaped indentations.
So, What factors should I take into account to assess the accuracy of the measured Vickers microhardness in this case?
Not homogeneous specimen can produce indentation like yours. Is your specimen porous?
Its either 1) Surface is not clean enough OR 2) Indenter could be faulty due to rough usage. Try to take the indentation on a fine (mirror) polished (upto 1500-2000 grit size) surface first and check the shape of the indent. If its proper then its the surface issue and if the indent is still not clear then the indenter is faulty and you may have to replace it. This issue can also happen if the material is soft and load applied is too high. Also, you may not get proper indent shape on the surfaces which are not metals/alloys.
In general, Vickers is an outdated testing method. If the material has many phases (ex: alpha, beta etc.), you may not get a proper microhardness value. I suggest you go for nano indentation but then again the equipment is expensive and available only in few top research facilities/institutions.
So, your best bet is to tally the results obtained from the Vickers tests with the previous literatures and approximation. Good luck
Vladimir Dusevich There is no porosity in my sample. It is an electroless coating surface. I have found perfectly square shaped indentations in other places on the same specimen. But, I want to know what should I do if I am getting such non-square indentation?
Vikas Marakini Thanks for the suggestion...Can I do nano-indentation testing on this sample? I am asking because it is a coated surface, so I cannot do polishing of this specimen.
I don't see any problem in doing nano ind on the surface to be tested. Check literatures. I don't see any problem with polishing the coated surface. It all depends on the depth (thickness) of your surface. If the coating is thick, you may loose only a few micron depth from the polishing process. Make sure the depth of the polishing doesn't exceed the coating layer. Try manual polishing carefully instead of equipment.
Vikash Kumar generally speaking, non-square indentations should not be considered when calculating Vickers microhardness.
Since the electroless-deposited surface is not homogeneous, you may want to select a low indentation load to minimize the indent size and the chance of getting defects.
Alternatively, nanoindentation would be a viable solution.
A porous sample may give similar results.
change the surface of the indentation to see if it gives the same results - if not, it means that it's the pyramidal base of the indenter that's deformed. So you need to check the deformation of the Vickers indenter tip.
Vikash Kumar if your sample is a coating, the load can surpass the 10% thickness, deforming in a inadequate way the substrate. Then, you can select a proper load to avoid this issue.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructures
- Thin Films