466
Y. Yoshida
around 110 K for pure Fe, the self-interstitials become mobile within the isochronal
annealing time, i.e., five min., annihilating with the vacancies, and subsequently
forming interstitial clusters. (c) At Stage II at around 150 K, the interstitial clusters
grow at impurities such as carbons, and finally (d) at Stage III at about 220 K, the
vacancies start migrating and disappearing at the interstitial clusters. There will be
further recovery stages above room temperature. Above 500 K, all the defects and
their agglomerates will disappear completely, as was observed by in-situ observation
of High Voltage Electron Microscope [40].
The Electron Microscope provides a possibility to find directly such defect clusters
and their creation and annihilation processes. Figure 9.19(e) shows an EM image
observed after Fe-ion implantation with the energy of 100 keV at room temperature.
M. Kiritani used a set of kinetic equations to analyze the growth kinetics of the defectclusters found by the High Voltage Electron Microscope. They successfully obtained
the mobility of vacancy in pure iron [40]: They measured the growth rate of the
vacancy loops, which were supposed to play a sink for the mobile interstitials in pure
Fe created by HVEM observations, i.e., in fact, electron irradiation with an energy of
2 MeV. They could compare the experimental results with the predictions simulated
from the set of kinetic equations. Finally, they could deduce the activation enthalpies
of the mobility of interstitials and vacancies as 0.3 eV and 0.6 eV, respectively.
They reported in the second publication [40] that the carbon impurities influence the
mobilities of vacancies and interstitials in the Fe matrix strongly so that the activation
enthalpy of the vacancy changes from 1.2 to 0.6 eV as the carbon concentration
decreases.
After neutron and electron irradiations of the
57 Co/
57 Fe-doped super-pure Fe-foils,
the Mössbauer emission spectra showed broad sextets without any isolated satellites,
which could assign to a vacancy and an interstitial associated
57 Co/
57 Fe probes.
The neutron irradiations at 30 K, however, provided the spectrum with a different
hyperfine field. The value was 35.0 (1) T higher than 33.8 (1) T due to regular site
in pure Fe. After the electron irradiations at 77 K, on the other hand, another sextet
appeared to possess the hyperfine field of 31.9 (1) T, being considerably lower than
that of the regular site. Consequently, there exist three different 57m Fe components
due to substitutional, vacancy, and interstitial sites, corresponding to 33.8 T, 35.0 T,
and 31.9 T, respectively. However, they appear not to be well-resolved from each
other at the first insight.
Furthermore, the thermal scanning in Fig. 9.18(a) shows that the counts through
Fe absorber at 77 K increases, as can be seen at around 110 K (Stage I) in the neutronirradiated specimen, suggesting the number of
57 Co trapped by the defects increases.
In contrast, the counts through Fe absorber at room temperature decreases due to the
formation of
57 Co/
57 Fe-interstitial clusters. In the case of the electron irradiation
with 2 × 10
18 electrons/cm
2 (Fig. 9.18(b)), on the other hand, the counts through Fe
absorber at 77 K decrease due to the annihilation reaction of mobile self-interstitials
with the vacancies, as is schematically shown in Fig. 9.18(b). At around 220 K (Stage
III), the counts through Fe absorber at 77 K increase again, suggesting a formation
of different defect clusters due to mobile vacancies. Finally, we found the recovery
Y. Yoshida
around 110 K for pure Fe, the self-interstitials become mobile within the isochronal
annealing time, i.e., five min., annihilating with the vacancies, and subsequently
forming interstitial clusters. (c) At Stage II at around 150 K, the interstitial clusters
grow at impurities such as carbons, and finally (d) at Stage III at about 220 K, the
vacancies start migrating and disappearing at the interstitial clusters. There will be
further recovery stages above room temperature. Above 500 K, all the defects and
their agglomerates will disappear completely, as was observed by in-situ observation
of High Voltage Electron Microscope [40].
The Electron Microscope provides a possibility to find directly such defect clusters
and their creation and annihilation processes. Figure 9.19(e) shows an EM image
observed after Fe-ion implantation with the energy of 100 keV at room temperature.
M. Kiritani used a set of kinetic equations to analyze the growth kinetics of the defectclusters found by the High Voltage Electron Microscope. They successfully obtained
the mobility of vacancy in pure iron [40]: They measured the growth rate of the
vacancy loops, which were supposed to play a sink for the mobile interstitials in pure
Fe created by HVEM observations, i.e., in fact, electron irradiation with an energy of
2 MeV. They could compare the experimental results with the predictions simulated
from the set of kinetic equations. Finally, they could deduce the activation enthalpies
of the mobility of interstitials and vacancies as 0.3 eV and 0.6 eV, respectively.
They reported in the second publication [40] that the carbon impurities influence the
mobilities of vacancies and interstitials in the Fe matrix strongly so that the activation
enthalpy of the vacancy changes from 1.2 to 0.6 eV as the carbon concentration
decreases.
After neutron and electron irradiations of the
57 Co/
57 Fe-doped super-pure Fe-foils,
the Mössbauer emission spectra showed broad sextets without any isolated satellites,
which could assign to a vacancy and an interstitial associated
57 Co/
57 Fe probes.
The neutron irradiations at 30 K, however, provided the spectrum with a different
hyperfine field. The value was 35.0 (1) T higher than 33.8 (1) T due to regular site
in pure Fe. After the electron irradiations at 77 K, on the other hand, another sextet
appeared to possess the hyperfine field of 31.9 (1) T, being considerably lower than
that of the regular site. Consequently, there exist three different 57m Fe components
due to substitutional, vacancy, and interstitial sites, corresponding to 33.8 T, 35.0 T,
and 31.9 T, respectively. However, they appear not to be well-resolved from each
other at the first insight.
Furthermore, the thermal scanning in Fig. 9.18(a) shows that the counts through
Fe absorber at 77 K increases, as can be seen at around 110 K (Stage I) in the neutronirradiated specimen, suggesting the number of
57 Co trapped by the defects increases.
In contrast, the counts through Fe absorber at room temperature decreases due to the
formation of
57 Co/
57 Fe-interstitial clusters. In the case of the electron irradiation
with 2 × 10
18 electrons/cm
2 (Fig. 9.18(b)), on the other hand, the counts through Fe
absorber at 77 K decrease due to the annihilation reaction of mobile self-interstitials
with the vacancies, as is schematically shown in Fig. 9.18(b). At around 220 K (Stage
III), the counts through Fe absorber at 77 K increase again, suggesting a formation
of different defect clusters due to mobile vacancies. Finally, we found the recovery