The effect of local chemical environment on the energetics of stacking faults and vacancy platelets in α-zirconium

The onset of breakaway irradiation growth in Zr and its alloys has been correlated with the nucleation and growth of faulted vacancy c-loops on basal planes. One theory for c-loop stabilization at high fluence is the reduction in stacking fault energy by solute or impurity segregation. This hypothesis is investigated through density functional theory calculations of the binding energy of Fe, Sn, Nb, Cr, and Ni to basal extrinsic, basal intrinsic or prismatic stacking faults in α-Zr. By means of a thermodynamic model, the ab initio binding energies have been correlated to segregation profiles and modified SFEs. Sn and Fe are shown to be tightly bound to basal stacking faults with only a weak interaction towards prismatic stacking faults. The corresponding segregation to faulted basal c-loops significantly reduces their formation energies and has the potential to stabilize these defects in the matrix. Based on the DFT calculations presented here, Nb, Cr, and Ni do not have a considerable effect on faulted c-loop formation energies. The binding energies of Fe, Sn, Nb, Cr, Ni, and H to a 19-vacancy platelet were additionally calculated to confirm the behavior of these elements with a nucleating c-loop defect. Fe and Cr in particular show strong binding to the periphery of this high-energy structure and correspondingly reduce the nucleation barrier for a vacancy c-loops. •Breakaway irradiation growth is correlated with faulted basal c-loop nucleation.•Solute segregation is demonstrated to reduce stacking fault energies.•Fe and Sn segregation reduces thermodynamic barrier for c-loop growth.•Sn only segregates to growing faulted c-loop loops and not c-loop precursors.•Fe and Cr segregation can stabilize c-loop precursors in the nucleation regime.