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Chapter VIII Micro-hardness studies…
load is decreased [13]. The constant ‘a’ is also known as the standard
hardness.
log P = log a + n log d (8.9)
The values of constants a and n are obtained from the plot of log P Vs
log d. Since the relation between log P and log d is linear, the slope of this line
gives the value of constant n and the intercept on log P axis gives the value of
log a and hence the value of a.
In order to analyze the ISE in the hardness testing, one needs to fit the
experimental data according to Kick's law. The behavior of the change in
micro-hardness with the applied load can also be studied by obtaining the
value of n. The variation of micro-hardness with load and its nature of the
value of n are widely studied for various materials. From the observations of
the variations of P with d Haneman and Schultz [67] have reported that in the
low load region, n generally has a value less that 2. Onitsch [68] also found
such low values of n by observing variation of micro-hardness with load, while
Grodzinski [69] had found variation of n values from 1.3 to 4.9 of various
materials. Knoop [70] observed an increase in hardness with decrease in load
where as, Campbell et al [71] and Mott et al [72] observed a decrease in
hardness with decrease in load. On the other hand, Taylor [73] and Toman et
al [74] have reported no significant change in the micro-hardness value with
variation of load. Such contradictory results [75] may be due to the effect of
the surface layers and vibrations produced during the test. Gane et al [31]
studied the micro-hardness at very small loads. They observed a sharp
increase in micro-hardness at small indentation size suggested that this
increase might be due to the high stresses required for homogeneous
nucleation in small dislocation free regions indented. On the contrary, Ivan'ko
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