Detection and quantification of solute clusters in a nanostructured ferritic alloy

•Simulated APT data indicate that solute clusters can be resolved at 80% detection efficiency.•Solute clusters containing 2–9 atoms were detected in a prototype ∼80% detection efficiency LEAP.•High densities, 1.8×1024m−3, of solute clusters were detected in as-milled flakes of 14YWT.•Lower densities, 1.2×1024m−3, were detected in the stir zone of a FSW.•Vacancies stabilize the clusters, which retard diffusion and confers excellent stability. A series of simulated atom probe datasets were examined with a friends-of-friends method to establish the detection efficiency required to resolve solute clusters in the ferrite phase of a 14YWT nanostructured ferritic alloy. The size and number densities of solute clusters in the ferrite of the as-milled mechanically-alloyed condition and the stir zone of a friction stir weld were estimated with a prototype high-detection-efficiency (∼80%) local electrode atom probe. High number densities, 1.8×1024m−3 and 1.2×1024m−3, respectively of solute clusters containing between 2 and 9 solute atoms of Ti, Y and O and were detected for these two conditions. These results support first principle calculations that predicted that vacancies stabilize these Ti–Y–O– clusters, which retard diffusion and contribute to the excellent high temperature stability of the microstructure and radiation tolerance of nanostructured ferritic alloys.