Abstract: Spherical nanoindentation of an iron-chromium-aluminum alloy was conducted to study the effect of ferric-ion (Fe³⁺) irradiation on the time-dependent plasticity behavior in the surface layers of this alloy. It was observed that the initiation of plasticity by the appearance of displacement burst or “pop-in” event occurred after a period of waiting time in the apparent elastic regime and that Fe³⁺ irradiation at 360 °C and up to ∼0.5 displacements per atom could make it happen under the lower applied loads but with a reduced magnitude. Through the experimental data, an activation volume and activation energy were extracted for the delayed plasticity. The results show that Fe³⁺-irradiation significantly reduced its activation volume from ∼3.05b³ to ∼1.75b³ (where b = Burgers vector), but slightly increased its activation energy from ∼0.65 to ∼0.71 eV. On the other hand, high-resolution scanning transmission electron microscopy observations reveal that the irradiation at the elevated temperature created interstitial atom pair onto the (100) habit plane that can serve as the nucleation site of a 〈100〉 dislocation loop while eliminating the pre-existing dislocations. Consequently, it is indicated that heterogeneous nucleation of the dislocation loop was predominant in the delayed plasticity initiation of this alloy and that the nucleation of the interstitial-type dislocation loop was involved due to Fe³⁺-irradiation.

Key words: Spherical nanoindentation, Delayed plasticity, FeCrAl alloy, Fe³⁺-irradiation