Compositional modifications in alloys under irradiation
Yacout, Abdel-Latif Mohamed
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https://hdl.handle.net/2142/20488
Description
Title
Compositional modifications in alloys under irradiation
Author(s)
Yacout, Abdel-Latif Mohamed
Issue Date
1990
Doctoral Committee Chair(s)
Stubbins, James F.
Department of Study
Nuclear, Plasma, and Radiological Engineering
Discipline
Nuclear Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Nuclear
Language
eng
Abstract
The complex interplay of several physical processes in altering the surface and subsurface compositions of alloys during irradiation has been investigated theoretically using a phenomenological model that includes preferential sputtering, displacement mixing, radiation-enhanced diffusion, radiation-induced segregation and Gibbsian adsorption. Sample calculations were performed for an Fe-Cr-Ni solid solution, representative of an austenitic stainless steel, under 3 keV Ne$\sp{+}$ sputtering. The effects of the different phenomena involved were examined in detail as functions of time and temperature. The results of these calculations were compared qualitatively with experiment. Experimental measurements of the surface and subsurface compositional changes in a Ag-40at%Au-20at%Cu alloy at temperatures between 30 and 600$\sp\circ$C, were compared with model calculations for the compositional changes in the alloy. From the comparison, useful information about the depth of origin of sputtered atoms and the defect properties in Ag-Au-Cu alloy system was derived. Radiation-induced precipitation during ion sputtering was investigated using the same kinetics model as applied for binary alloys. Special space transformations were applied to accommodate for the moving boundaries of the precipitate layer appearing during irradiation. The growth of the $\gamma$-Ni$\sb3$Si precipitate formed during 100 keV Si$\sp{+}$ irradiation of Ni-Si alloys was studied. Predictions of the behavior of the layer under different fluxes and temperatures were discussed. Finally, ion-implantation in concentrated binary alloys was investigated and model calculations for the implantation of 50 keV Si$\sp{+}$ into Ni were performed. The calculations took into account the time dependence of the damage profile, implanted ions profile and the sputtering coefficients, through updating them at different periods of time during irradiation. Comparing the implanted Si$\sp{+}$ concentration profiles calculated with the dynamical changes in the damage and ion distributions and in the coefficients taken into account, to the concentration profiles calculated without updating, noticeable changes between the two cases were observed after long periods of irradiation. Although the changes in the calculated damage and ion profiles at the different periods were not pronounced, the observed changes suggested the importance of updating these profiles and the sputtering coefficients during irradiation.
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