Influence of ions irradiation on the microstructural evolution, mechanical and tribological properties of Zr-4 alloy

The wear of fuel cladding due to flow induced vibration in nuclear reactor presents a safety concern, and the impact of neutron irradiation on wear behavior is not fully understood. In this study, Kr⁺ and Zr⁺ ions bombardment were used to simulate the neutron irradiation on Zr-4 alloys, and the impacts of ion irradiation on the microstructure evolution, mechanical and tribological behaviors of Zr-4 alloy were investigated. The HRTEM observation reveals that high density of point defects, dislocations as well as small dislocation loops formed below the surface within 260 nm depth after Zr⁺ irradiated with the damage level up to 30 dpa. The nano-indentation tests suggests that the hardness of Zr-4 alloy increases with increasing of irradiation dose, resulting from the inhibition of slip of dislocation under the large amount of defects induced by irradiation. The fretting wear tests show that the friction coefficient of Zr-4 alloy increases significantly from 0.4 to above 1, due to the irradiation hardening and embrittlement, the repeated sliding during fretting wear leads to intergranular fracture at surface and the growth of cracks under load contact area, leaving deeper furrows and higher hardness debris, which results in higher friction coefficient and severe wear of Zr-4 alloy after irradiation.