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Chapter VIII Micro-hardness studies…
The first order elastic stiffness constant (C11) has been evaluated for pure
and amino acid doped KDP crystals using Wooster’s empirical relation [65] as
follow:
log C11 = (7/4) log Hv (8.7)
Where, Hv is micro-hardness. The values of C11 are tabulated in table (8.2).
This supports the concept of Onitsch [66], that if n < 2 the micro-
hardness number decreases as the load increases. In low-load regions the
resistance offered by material may be comparable with the applied load,
resulting in a higher value of hardness. However, at higher load the plastic
flow of the material may be higher and hence the resistance offered by the
material is negligible, thus the value of hardness decreases with increase in
the value of applied load.
8.5 Study of Mayer's law or Kick's law:
Variation of micro-hardness with applied load is usually explained for
spherical indenter by Meyer's law [6] and pyramidal indenter by Kick's law
[13]. Later on Kick's law was modified by Hay and Kendall [14], which is
discussed in next section of this chapter. For pyramidal indenter Kick's law is
given as,
P = ad n
301
(8.8)
Where, P is the applied load in gram (or Newton), d is the observed diagonal
length of indentation mark, and n is the constant for a given material. Kick
postulated a constant value of n= 2 for all the indenters and for all
geometrically similar impressions. Nevertheless, Kick’s law did not receive
wide acceptance on account of the fact that n usually has a value less than 2,
particularly in the low load regions. If n is less than 2, the hardness number
increases with decreasing load, and if n is greater than 2, it decreases as the