Oxygen trapping in defect clusters in Fe and FeCr alloy by ion channeling and ab-initio study

Ion channeling experiment and ab-initio density functional theory (DFT) calculations are used to study O interactions with interstitial and vacancy clusters in Fe and FeCr alloy. Chromium and O ¹⁸ ions are implanted at the same depth in a Fe crystal and annealed at 400 °C. Lattice location of O ¹⁸ is found to be tetrahedral interstitial site by nuclear reaction analysis (NRA)/channeling and Cr is found at substitutional site with small displacement by particle induced X-ray emission (PIXE)/channeling experiment. DFT calculations predict similar sites of O ¹⁸ and Cr for trapping in self-interstitial clusters. On the other hand, O ¹⁸ is implanted in a Fe15at%Cr alloy and annealed at 400 °C. The O ¹⁸ is found to be displaced 0.6 Å along <100> from the octahedral interstitial site in FeCr alloy. DFT calculations predict similar lattice location of O for trapping in vacancy clusters. The Cr atoms show strong influence on the O trapping at defects in FeCr alloy.