Effect of phosphorus on vacancy-type defect behaviour in electron-irradiated Ni studied by positron annihilation

Ab initio study of phosphorus effect on vacancy-mediated process in nickel alloys – An insight into Ni2Cr ordering

“…It has been shown in earlier studies that solute or impurity atoms having a vacancy binding energy more negative than −0.2 eV will induce the formation of vacancy clusters under non-equilibrium conditions such as cold work or irradiation [81,82]. The first-principles calculation of vacancy-phosphorus interaction in this study is in generally good agreement with the previous experimental work, showing the strong tendency of phosphorus atoms to interact and form vacancy aggregation under electron irradiation [17]. Similar results suggesting the strong vacancy-phosphorus interaction were also found in austenitic steels [16,23,24].…”

“…For the 0.017 wt.% P alloy the start of the transformation at 450°C was ~2 times faster than the low P alloy, and ~120 times faster for the 0.078 wt.% P alloy. The acceleration is unexpected considering the strong binding between phosphorus and vacancies in both bcc and fcc alloys [13][14][15][16][17][18][19][20][21] that is generally known to reduce available and freely-migrating vacancies for diffusional processes. The enhanced precipitation or diffusion kinetics via alloying with phosphorus was observed in other alloy systems as well.…”

“…Solutes with strong vacancy binding favors the formation of vacancy-solute pairs but reduce the effective number of vacancies for atomic transport via solute trapping, and therefore the ordering transformation rate decreases [9]. However, the conventional understanding is in contradiction with the accelerated ordering by alloying phosphorus, which is generally known to have strong binding with vacancies in the fcc Ni [17]. Indeed, the previous treatment may not able to produce consistent agreements with experiments over a wide range of solutes and alloys as it neglected other important solute-modified properties, particularly the solute effects on the atom-vacancy exchange frequency and vacancy formation energy in the vicinity of a solute atom.…”