Mechanism of void formation in grain interior of ODS alloys

The mechanism of the void formation in the grain interior of ODS alloy PM2000 was investigated by an internal friction technique. A relaxation peak with a relaxation characteristic was observed around 770 °C, and average activation energy for the relaxation peak is approximately 2.70 ± 0.16 eV, which is consistent with that of self-diffusion in δ-ferrite. Internal friction study has substantiated the existence of the interfacial diffusional relaxation of the stress concentrations in the single crystal ODS alloy. The micrographic results indicate that the actual shape for the voids, which co-exist with the oxide particles in the voids, is ellipsoidal. Taking account of the correlation of the interfacial diffusional relaxation with the ellipsoidal shape of voids, it is suggested that the void formation in grain interior is attributed to the relaxation of the stress-concentration gradients introduced by extrusion deformation via interfacial diffusion.