Stability of Y–Ti–O precipitates in friction stir welded nanostructured ferritic alloys

Nanostructured ferritic alloys, which have complex microstructures consisting of ultrafine ferritic grains with a dispersion of stable oxide particles and nanoclusters, are promising materials for fuel cladding and structural applications in the next generation nuclear reactor. This study evaluates microstructure of friction stir welded nanostructured ferritic alloys using electron microscopy and atom probe tomography techniques. Atom probe tomography results revealed that nanoclusters are coarsened and inhomogeneously distributed in the stir zone and thermomechanically affected zone. Three hypotheses on coarsening of nanoclusters are presented. The hardness difference in different regions of friction stir weld has been explained.