DEFECT BUILDUP AND SOLUTE SEGREGATION IN ALLOYS UNDER PULSED IRRADIATION

The Johnson-Lam kinetic model, which is based on a combination of diffusion and chemical reaction rate equations, has been used to study the buildup of point defects and defect-solute complexes, and segregation of minor elements in alloys under pulsed irradiation. Concentrations of defects and solutes have been calculated for various defect-production rates, defect-solute binding energies and pulse durations, with Ni as the model material. Precipitation at the sink surface is taken into account when the solute concentration at the sink exceeds the solubility limit. For a fixed damage rate, the longer the pulse duration the smaller the number of cycles needed to achieve a cyclic state for defects and defect-solute complexes and quasi-steady state for solute segregation. In addition, for a fixed pulse duration, the higher the damage rate the fewer the cycles required to observe these states. The resultant solute segregation obtained under pulsed irradiation can be similar to, or different from segregation achieved during steady irradiation depending on whether the beam-off period is comparable to, or much longer than the pulse duration. The microstructures of the material can also be different from those formed by unpulsed bombardment due to cyclic production and annealing of mobile defects. © 1978.