부산대학교 도서관

When alloys based on the Fe-Ni-Cr system are subjected to irradiation at high temperatures a substantial amount of elemental segregation occurs. Two categories of segregation have been observed, one involving radiation-induced precipitation or changes in precipitate composition, and another involving the establishment of compositional gradients near microstructural sinks. While segregation into precipitate phases is known to strongly influence the development of void swelling, it now appears that segregation to void surfaces plays an equally important role in the development of voids. A general feature of both types of segregation is the major role of nickel as a primary segregant.
An investigation of the basic flux equations for diffusion of interstitials and vacancies in superimposed strain and composition gradients shows that several previously unconsidered drift terms arise in the description of the bias as a result of elemental segregation. These terms originate from the compositional dependence of point defect formation and migration energies and the compositional dependence of elastic properties and lattice parameter. When compounded with the operation of the inverse Kirkendall segregation mechanism, these terms strongly alter the bias for void nucleation and growth and provide an explanation for the marked variation of void nucleation and swelling with nickel concentration. The segregation-induced drift terms are comparable in magnitude to the strain-induced drift terms and are strongly dependent on nickel concentration. This is demonstrated for binary Fe-Ni alloys using published tracer diffusion and thermodynamic data.