Burst and Biaxial Creep of Thin-Walled Tubing of Low c/a-Ratio HCP Metals

AbstractThin-walled tubing used in various structures are made of low c/a-ratio hcp metals such as Zr and Ti based alloys, and their integrity to internal pressures is of prime importance in the life of these engineering structures. We summarize here ome of the work performed on Zircaloy cladding commonly used in LWRs as thin walled tubing as well as Cp-Ti and Ti3Al2.5V that find applications in aerospace industry. Considered here are three different types of tests: (i) burst tests using closed- end internal pressurization, (ii) uniaxial ring tests for characterization of hoop creep properties and (iii) hoop creep under biaxial internal pressurization. Burst and ring tests yielded identical hoop creep and rupture characteristics indicating the utility of ring tests to replace burst tests. Importance of transitions in creep mechanisms with decreased stress levels in predicting in-service dimensional changes is emphasized

Ion irradiation enhances the mechanical performance of metallic glasses

We demonstrate that irradiation may enhance the plasticity in metallic glasses by increasing the free-volume content via micropillar compression experiments on an ion-irradiated bulk metallic glass (BMG). Results show that irradiation decreases the flow stress and enhances the shear band formation by lowering the magnitude of stress serrations in plastic flow regime. These results highlight that amorphous alloys can mitigate the deleterious affects of severe ion irradiation as compared to their crystalline counterparts

Unfaulting mechanisms of Frank loops in fluorite oxides

Unfaulting of Frank loops in irradiated fluoride oxides are of significance to microstructural evolution. However, the mechanisms have not been directly observed. To this end, we utilize molecular dynamics to reveal the atomistic details related to the unfaulting process of interstitial Frank loop in ThO$_2$, which involve nucleation of single or multiple Shockley partial pairs at the loop circumference. The unfaulting is achieved via a synchronous shear of the partial pairs to remove the extrinsic stacking fault in the cation sublattice and the intrinsic stacking fault in the anion sublattice. The strong oxygen motion at the dislocation core may reduce the activation barriers of dislocation nucleation and migration. These findings provide a fundamental understanding of the transformation of faulted loops in irradiated ThO$_2$, and could be transferable to other fluorite systems