Characterizing Dislocation Loops in Irradiated Zr alloys by X-ray Line Profile Analysis of Diffraction Patterns with Satellites

In this work we extend the convolutional multiple whole profile (CMWP) line profile analysis (LPA) procedure to determine the total dislocation density and character of irradiation-induced dislocation loops in commercial polycrystalline Zr specimens. Zr alloys are widely used in the nuclear industry as fuel cladding materials in which irradiation-induced point defects evolve into dislocation loops. LPA has long been established as a powerful tool to determine the density and nature of lattice defects in plastically deformed materials. The CMWP LPA procedure is based on the Krivoglaz-Wilkens theory in which the dislocation structure is characterized by the total dislocation density and the dislocation arrangement parameter, ρ and M. In commercial Zr alloys irradiation-induced dislocation loops broaden peak profiles mainly in the tail regions and occasionally generate small satellites next to the Bragg peaks. In this work we have solved the two challenges in powder diffraction patterns of irradiated Zr alloys: (a) we have made determination of the M values from the long tail regions of peaks unequivocal and (b) have fitted satellites separately, using physically well-established principles, in order to exclude them from the dislocation determination process. Referring to the theory of heterogeneous dislocation distributions we have justified determination of the total dislocation density from the main peaks free from satellites. We characterize the dislocation loop structure by the total dislocation density of loops and the M parameter correlated to the dipole character of dislocation loops. The extended CMWP procedure is applied to determine the total dislocation density, the dipolecharacter of dislocation loops and the fractions of <a> and <c> type loops in proton or neutron irradiated polycrystalline Zr alloys used in the nuclear energy industry.