Thesis-1995-Song.pdf (3.87 MB)
Radiation-induced grain boundary segregation in dilute alloys
thesis
posted on 2012-09-27, 11:17 authored by Shenhua SongModelling of irradiation-induced segregation or thermal non-equilibrium
segregation needs data on the impurity-point defect binding energy. These values
are generally unavailable. In this work, an initial approach to determining impurityinterstitial
binding energies in metals is established with some success on the basis
of strain field arguments and the earlier work is slightly modified for more accurate
calculations of oversized impurity-vacancy binding energies. The method is applied
to predictions of various impurity-point defect binding energies in several transition
metal matrices. With the aid of the predictions, some experimental results on
radiation-induced segregation are reasonably satisfactorily interpreted.
A radiation-induced grain boundary segregation (RIS) model is established for
dilute alloys based on the complex mechanism and combined with McLean's
equilibrium segregation model. In the model, radiation-enhanced solute diffusion is
taken into consideration. Theoretical predictions are made for segregation of
phosphorus in the neutron-irradiated a-Fe matrix. There exists a segregation
transition temperature below which combined radiation-induced non-equilibrium
and radiation-enhanced equilibrium segregation is dominant, and above which
thermal equilibrium segregation is dominant; peaks in the temperature dependence
of segregation shift to lower temperatures with decreasing neutron dose rate and/or
increasing neutron dose; the combined radiation-induced non-equilibrium and
radiation-enhanced equilibrium peak segregation temperature and the thermal
equilibrium peak segregation temperature are about 150 and 550°C, respectively,
for phosphorus grain boundary segregation in the a-Fe matrix at neutron dose rate
= 10-6 dpa/s and neutron dose = I dpa .
Grain boundary segregation of solutes in the neutron-irradiated and unirradiated
(thermally aged) 2.25Cr1Mo steels doped with P and Sn is examined by means of
field emission gun scanning transmission electron microscopy (FEGSTEM) which
has very high spatial resolution (- 1 nm). The material is irradiated to a dose of
0.042 dpa at a dose rate of 1.05 x 10-8 dpa/s in a swimming pool-type light-water
research reactor in the Paul Scherrer Institute (PSI) of Switzerland. Grain boundary
microanalysis is performed in the Nuclear Electric Berkeley Technology Centre of
the UK. Comparison of the experimental and predicted results shows that the
predictions are generally consistent with the observations.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Materials
Publisher
© S SongPublication date
1995Notes
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough UniversityLanguage
- en