(a) 100 µm - Helmholtz-Zentrum Berlin

4.1 Interlayer 61
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t [h ] A
Figure 4.9: The radius of a single grain rG as a function of the annealing time tA for
a specimen type C annealed at TA = 400 °C. The grain becomes visible at the nucleation
time tN. The grain growth velocity increases until the final, constant grain growth velocity
vG,0 is obtained.
by calculating the average value. The grain growth velocity for specimen A is
0.227 ± 0.028 µm/min. For both the other specimens the grain growth velocity was
found to be approximately equal at 0.077 ± 0.006 µm/min and 0.076 ± 0.001 µm/min
for samples type B and C, respectively. The grain growth velocity is similar for all
grains in the same experiment. All grains in the same experiment nucleate at
approximately the same time.
In Fig. 4.11 the density of grains NG is shown as a function of the annealing time
for a specimen of type C annealed at 450 °C. The density of grains is very low
at the end of the process indicating the very large grain size. Three different
phases of the process are marked. In phase (I) no grains are visible. In phase
(II) nucleation takes place and these grains grow, thus this phase is referred to as
nucleation phase. After a certain time the nucleation comes to an end. The existing
grains continue to grow until the layer exchange is completed. This phase (III) is
referred to as growth phase. The process time in case of the sample in Fig. 4.11
is about 43 h (Fig. 4.6). Depending on the process parameters the phases have