Page 105 - Zmist-n3-2015-new

Fig. 3. Micro-Raman spectra of 50 mN (a) and 500 mN indentation (b),
acquired from the surface (spectra 1, 3) and from some depth (spectra 2, 4);
spectra 1, 2 – short holding, and spectra 3, 4 – long holding indentations.
The fact that “kink pop-out” is more rarely displayed for 50 mN indentations than
for 100 mN ones can be explained by smaller dislocation region, in which the develop-
ment of the necessary conditions for the formation of the amorphous phase is less pro-
bable.
For 500 mN indentations the increase of holding time leads to the intensification
of Si-III and Si-XII peaks as well, if compared with the initial Si-I peak, especially at
the surface. This is consistent with our previous work on prolonged holding during
Vickers quasistatic indentation showing the same results [15]. The broadening of Si-I
–1
peak at 301 cm displayed for 50 mN indentations may be due to the increasing degree
of structural disorder due to the high density of dislocations.
Displacement-time dependences during creep. The analysis of displacement-time
dependences during holding at the peak load (P max) displayed some peculiarities of
creep process. The penetration depth versus time curves and the respective instanta-
neous creep rate (derivative dh/dt) versus time curves for 50 and 500 mN indentations
are shown accordingly in Fig. 4 (a, b) and (c, d). It is clearly seen from the curves
presented that the creep process has 2 distinctive stages: the first one distinguished by
higher and at the same time decelerating creep rate and the second, steady-state creep
stage, where the creep rate becomes almost constant with a slight decreasing tendency.

Fig. 4. Displacement-time dependences (a, c) and creep rate versus time dependences (b, d)
during creep for 50 mN (a, b) and 500 mN (c, d).
The initial creep rate appears to depend on the load applied and it is higher (~ 4 nm/s)
for larger peak load (500 mN) indentations against ~ 1 nm/s for 100 and 50 mN inden-

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