Non-Effective Testing Method Of A Microhardness Case Study On 2PPA Single Crystals

Measurement of hardness is a useful non-destructive testing method used to determine the applicability of the crystal in the device fabrication. Microhardness study was carried out on 2PPA single crystal using a Vickers microhardness tester fitted with a Vickers diamond pyramidal indenter in order to evaluate its mechanical stability. The static indentations were made at room temperature and 323 K with a constant indentation time of 5 s for all indentations. As grown polished sample of 2PPA was used for the study. The indentation marks were made on the flat, smooth and prominent faces by varying the load from 10 to 50 g at room temperature and 323 K. Since the 2PPA crystal melts at 152 oC the crystal was heat treated up to 50 oC. The Vicker’s
9. It is clear that the microhardness number increases with increasing load. It is evident from the above plot that the microhardness number of the crystal increases with increase in load which is in agreement with the reverse indentation size effect (ISE) [15] and also decreases with increase in temperature. The decrease in the value of hardness number with respect to increase in temperature can be attributed to the fact that, when the temperature increases, the average inter atomic distance becomes greater than that at room temperature due to lattice vibration. This leads to more and more lattice phonon interactions which causes the breaking of bond as well reduce the hardness value [16]. The maximum value of hardness number observed for 2PPA, crystal is 39.9 kg/mm2 at 50 g (room temperature) respectively. The load above these values develops multiple cracks on the crystal surface due to the release of internal stresses generated locally by
The simplest way to describe the ISE is Meyer’s law. For the normal ISE behavior, the exponent n < 2.When n > 2, there is the reverse ISE behavior. When n = 2, the hardness is independent of the applied test load, and is given by Kick’s law [18]. Plots obtained between log (P) and log (d) for 2PPA single crystal at room temperature is a straight line and is shown in Fig. 10. The value of ‘n’ obtained for 2PPA single crystal using linear fit is found to be 2.52 respectively. This is also in good agreement with RISE [15]. On careful observations made on various materials, Onitsch and Hanneman [19] pointed out that ‘n’ lies between 1 and 1.6 for hard materials, and it is more than 1.6 for soft materials. The value of ‘n’, obtained for 2PPA single crystals is found to be 2.52, which reveals that the material is