The design of Pd-containing high-entropy alloys and their hardening behavior under He ion irradiation

Imparting additional chemical heterogeneities of high-entropy alloys (HEAs) is considered as a novel strategy to improve their irradiation resistance on dislocation loop growth; however, there is still a lack of knowledge about the effects of this strategy on bubble evolution and irradiation-induced hardening. In this study, a series of Pdcontaining FeCrNiCo HEAs with proven potential for chemical short-range order were designed and irradiated by 400 keV He ions to the fluences of 5 x 1016 cm-2, 1 x 1017 cm-2, and 5 x 1017 cm- 2 at 723 K. Microscopic characterization demonstrates a remarkably inhibited growth of dislocation loops and promoted bubble coarsening in the Pd-containing HEAs compared to the HEA without Pd alloying. The underlying mechanism is that although the alloying of Pd can suppress the evolution of dislocation loops through severe local lattice distortion, it also significantly reduces the vacancy formation energy of the entire HEA system, leading to the encouraged bubble evolution. Pd-containing HEAs exhibit improved resistance to irradiation-induced hardening at low doses, but this advantage is unexpectedly absent with increasing dose. The hardening mechanism is explained by identifying the loop-dominated hardening at low dose and the bubble-induced hardening which makes an increased contribution at high dose. In addition, the Ni segregation around bubbles and loop punching mechanism are also discussed to provide essential evidence. These insights can help to shed light on the effects of Pd alloying on bubble evolution and irradiation-induced hardening behavior in HEAs, and thus contribute to the design of irradiation-resistant HEAs.