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Chapter VIII Micro-hardness studies…
savings of time, one of the main advantages of the Knoop test is that it can
test thin layers more easily. For surfaces with varying hardness, such as in
case of hardened parts, the Knoop indents can be spaced closer than Vickers
indents. Thus, a single Knoop traverse can define a hardness gradient more
simply than a series of two or three parallel Vickers traverses in which each
indent is made at different depths. Furthermore, if the hardness varies
strongly with the depth, the Vickers indent is distorted by this change; i.e., the
diagonal parallel to the hardness change is affected by the hardness gradient,
while the diagonal perpendicular to the hardness gradient remains unaffected.
5. Nano-identation
The nano-indentation is used for measuring hardness at very small
length scales. The commonly used indenter for nano-indentation is the
Berkovich diamond indenter which is a triangular diamond pyramid. In this,
the lateral dimension of the contact impression is approximately seven times
the depth. So, the measurements are possible for contact impressions with
lateral dimensions 0.1 µm. A detailed procedure for the determination of
mechanical properties of very thin coatings and films using the nano-
indentation technique was first described by Oliver and Pharr [12].
8.3 Experimental Technique
Pure and various amino acids ((L-histidine, L-threonine, DL-
methionine) doped KDP crystals were subjected to Vickers micro-hardness
studies. Indentations were made on smooth (100) faces. The Vickers micro-
hardness tester is shown in figure (8.3 a). The instrument comprises of
microscope with a filar micrometer eyepiece (least count 0.0001428 mm)
mounted on a stand. A loading and unloading mechanism is attached to the
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