The effect of dual Fe+/He+ ion beam irradiation on microstructural changes in FeCrAl ODS alloys

Nanostructured ferritic oxide dispersion strengthened (ODS) alloys contain a high density of Y-Al-Ti-O nanoparticles, high dislocation densities and fine grains. Structural analysis with HRTEM shows that the composition of the initial Y2O3 oxide is modified to perovskite YAlO3 (YAP), Y2Al5O12 garnet (YAG) and Y4Al2O9 monoclinic (YAM) particles.
Irradiation of these alloys was performed with a dual beam implantation of 2.5 MeV Fe+ and 350 keV He+, either simultaneously or sequentially.
Additionally, the He+ concentration was varied between 18 and 72 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. A clear hardness increase in the irradiated area is observed by nanoindentation in every ion implantation regime. Hardness ratios of irradiated relative to non-irradiated ODS materials and the appearance of hardness maxima close to the surface region are discussed in detail. The irradiation induced hardening effect is stronger for a heat treated HT-ODS alloy than for an as-received one. The large difference in the hardness data of as-received ODS for simultaneous and sequential implantation can be explained by point defect recombination at dislocations and grain boundaries occurring for sequential irradiation.