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

Revealing hidden defects through stored energy measurements of radiation damage

With full knowledge of a material’s atomistic structure, it is possible to predict any macroscopic property of interest. In practice, this is hindered by limitations of the chosen characterization techniques. For example, electron microscopy is unable to detect the smallest and most numerous defects in irradiated materials. Instead of spatial characterization, we propose to detect and quantify defects through their excess energy. Differential scanning calorimetry of irradiated Ti measures defect densities five times greater than those determined using transmission electron microscopy. Our experiments also reveal two energetically distinct processes where the established annealing model predicts one. Molecular dynamics simulations discover the defects responsible and inform a new mechanism for the recovery of irradiation-induced defects. The combination of annealing experiments and simulations can reveal defects hidden to other characterization techniques and has the potential to uncover new mechanisms behind the evolution of defects in materials.Peer reviewe

Revealing hidden defects through stored energy measurements of radiation damage

With full knowledge of a material’s atomistic structure, it is possible to predict any macroscopic property of interest. In practice, this is hindered by limitations of the chosen characterization techniques. For example, electron microscopy is unable to detect the smallest and most numerous defects in irradiated materials. Instead of spatial characterization, we propose to detect and quantify defects through their excess energy. Differential scanning calorimetry of irradiated Ti measures defect densities five times greater than those determined using transmission electron microscopy. Our experiments also reveal two energetically distinct processes where the established annealing model predicts one. Molecular dynamics simulations discover the defects responsible and inform a new mechanism for the recovery of irradiation-induced defects. The combination of annealing experiments and simulations can reveal defects hidden to other characterization techniques and has the potential to uncover new mechanisms behind the evolution of defects in materials.Peer reviewe

Effect of hydriding on the creep behavior of HANA-4 Zirconium alloy

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Nanoindentation response of an ion irradiated Zr-based bulk metallic glass

Nanoindentation experiments were conducted on a Ni+ ion-irradiated Zr-based bulk metallic glass (BMG). The irradiation was carried out using 2.5, 5, 10 and 15 MeV ions and a flux of similar to 10(16) ions/cm(2). Post mortem imaging of the indents reveals a transition in the deformation mechanism of the irradiated regions from heterogeneous shear banding to homogeneous flow. Additionally, the load-displacement curves exhibit a transition from serrated to continuous flow with increasing severity of irradiation damage. The stress-strain response obtained from micro-pillar compression experiments complements the indentation response exhibiting a decrease in the flow stress and an `apparent' strain hardening at the lowest irradiation damage investigated, which is not observed in the as-cast alloy. (C) 2011 Elsevier B.V. All rights reserved

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

Near-surface modification of defective KTaO3 by ionizing ion irradiation

International audienceThe synergistic effect of nuclear (Sn) and electronic (Se) energy loss observed in some ABO3 perovskites has attracted considerable attention due to the real possibility to modify various near-surface properties, such as the electronic and optical properties, by patterning ion tracks in the defective near-surface regions. In this study, we show that low-energy ion-induced disordering in conjunction with ionizing ion irradiation (18 MeV Si, 21 MeV Ni and 91.6 MeV Xe) is a promising approach for tailoring ion tracks in the near-surface of defective KTaO3. Experimental characterization and computer simulations reveal that the size of these latent ion tracks increases with Se and level of pre-existing damage. These results further reveal that the threshold Se value (Seth) for track creation increases with decreasing pre-damage level. The values of Seth increase from 5.02 keV nm−1, for a pre-existing fractional disorder of 0.53 in KTaO3, to 10.81 keV nm−1 for pristine KTaO3. Above these thresholds, amorphous latent tracks are produced due local melting and rapid quenching. Below a disorder fraction of 0.08 and Se ⩽ 6.68 keV nm−1, the synergistic effect is not active, and damage accumulation is suppressed due to a competing ionization-induced damage annealing process. These results indicate that, depending on Se and the amount of pre-existing damage, highly ionizing ions can either enhance or suppress damage accumulation in KTaO3, thus providing a pathway to tailoring defects states. Comprehending the conflicting roles of highly ionizing ions in defective ABO3 oxides is vital for understanding and predictive modeling of ion-solid interactions in complex oxides, as well as for achieving control over ion track size in the near-surface of defective KTaO3