As per the definition, Hardness is the resistance to the deformation. But, deformation can be seen in plastic materials only. ceramics are brittle in nature. So, the material will break when it crosses elastic limit
So, I want to know
1. How is hardness of ceramics calculated?
Especially for superhard coatings
"Hardness is resistance to deformation" is a loose definition. It is true that during hardness testing a permanent indentation is created by plastic deformation of material. Ceramics undergo plastic deformation - the magnitude may be much less than that of metals. For example, MgO (especially single crystals) can be plastically deformed at room temperature to about 10% (Ref: Mechanical Properties of Ceramics, Joshua Pelleg, Springer 2014).
Since diamond is the hardest materials known to the engineering community with a hardness of ~10,000 kg/mm2 or 90 - 100 GPa) diamond indenters are used for measuring hardness of ceramics (typical hardness
Dear Dr. Sathish Kumar,
I suggest you to have a look at the following interesting papers:
-On the measurement of hardness of super-hard coatings
A.C. Fischer-Cripps, P. Karvánková, Stanislav Vepřek
Surface and Coatings Technology 200(18-19):5645-5654 (2006)
DOI: 10.1016/j.surfcoat.2005.07.096
Available on Research Gate at: https://www.researchgate.net/publication/229184082_On_the_measurement_of_hardness_of_super-hard_coatings
-Toward hard yet tough ceramic coatings
Yu Xi Wang, Sam Zhang
Surface and Coatings Technology, Vol. 258, 15, Pages 1-16 (2014)
Available at: https://www3.ntu.edu.sg/ThinFilms/mae-thinfilms/Thinfilms/pdfpapers/hardYETtough.pdf
Best regards, Pierluigi Traverso
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