Dual-beam irradiation of friction stir spot welding of nanostructured ferritic oxide dispersion strengthened alloy

Nanostructured ferritic oxide dispersion strengthened (ODS) alloys usually contain a high density of Y–Al–O and Y–Ti–O nanoparticles, high dislocation densities and fine grains. Friction stir spot welding (FSSW) is a very promising technique for the joining of ODS materials without oxide particle agglomeration and loss in mechanical properties in the weld zone. Heating and severe plastic deformation can significantly alter the originally as-received material. The local microstructure determines the weld mechanical properties, which are analyzed by nanoindentation. The FSSW region consists of three different zones: the base material, the thermo-mechanically affected zone and the heat affected zone. Irradiation of the FSSW area was performed with a Fe+/He+ dual ion beam. Hardness changes within the welding zones and variation with irradiation damage are discussed.

► FSSW has been successfully applied to join two sheets of ODS material.
► Dynamic recrystallization occurs in the thermo mechanically affected zone, resulting in a decrease in hardness.
► After irradiation, a clear maximum is visible in all depth dependent hardness charts, which is caused by defects generated during ion bombardment.
► The material changes during FSSW are larger than the radiation induced hardness increase.