Effects of Hydride Morphology on Zr-2.5Nb Fracture Toughness

Abstract

The effects of hydride morphology on the axial fracture toughness of cold-worked Zr-2.5Nb pressure tube material have been determined between room temperature and 240°C. Tests were performed on small compact tension specimens machined from samples of material prepared with different morphologies and hydrogen concentrations. The morphologies were characterized by a parameter referrred to as the hydride continuity coefficient (HCC), which provides a measure of the extent to which hydrides are oriented in the axial-radial plane of the pressure tube. Hydrides in this orientation are known to be detrimental to the fracture properties of the tube. Fracture toughness was characterized by a J-R curve technique, from which it is possible to estimate the maximum stable size of a through-wall axial crack for typical reactor operating conditions. Material with HCC values greater than 0.5 exhibited low toughness from room temperature to 240°C, at which temperature there was an abrupt transition to an upper shelf toughness value. As HCC decreases, the transition to upper shelf toughness occurs more gradually and is complete at a lower temperature.

Bioinertness and fracture toughness evaluation of the monoclinic zirconia surface film of Oxinium™ femoral head by Raman and cathodoluminescence spectroscopy

“…This means that, if the substrate is highly tough and compliant, the crack will arrest at the interface and will remain confined into limited surface regions. The substrate of Oxinium™ femoral head components is a quite ductile Zr-2.5%Nb alloy and its fracture toughness can be estimated in the order of 75-96 MPa  m 1/2 (Coleman et al, 1989;Walker, 1972;Wallace et al, 1989), which is comparable with that of steel (Roy et al, 2008), and an order-of-magnitude higher than that of the surface oxide fracture toughness and of that of any bulk ceramic used in biomaterial implants. Therefore, any crack, occasionally formed as a consequence of extrinsic factors, on the Oxinium™ surface not only will remain confined in its depth within the oxide film but will also hardly spread through the surface of the oxide film, which proves the extremely high structural reliability of the Oxinium™ joint components in comparison with bulk zirconia ceramic components.…”

Fracture Strength of Embedded Hydride Precipitates in Zirconium and its Alloys

“…It is significant that results of fracture toughness tests of compact toughness specimens of unirradiated and irradiated material containing radial hydrides reproduced in Figs. 9.14 and 9.15, similarly show that 250°C is approximately the temperature where these hydrides no longer act as fracture initiation sites, and, therefore, no longer primarily contribute as nucleation sources for the overall ductile failure of the specimen [47,51].…”

Ductile-to-Brittle Transition Temperature for High Burnup Zircaloy-4 and ZIRLO (TM) Cladding Alloys Exposed to Simulated Drying Storage Conditions.

“…However, even if such data were available, high susceptibility to radial-hydride formation would likely be the result of the RXA microstructure and low hydrogen content (≈100 wppm or less) rather than the presence of Nb. Data reported by Wallace et al [11] indicate that a relatively high tensile stress is required to induce significant radial-hydride precipitation during cooling of CWSRA Zr-2.5%Nb with 60 to 80 wppm hydrogen. Although possible, it is unlikely that the presence of Nb in ZIRLO™ is responsible for the higher susceptibility to radial hydride precipitation observed in high-burnup ZIRLO™.…”

“…The radial hydride fraction (RHF, percent of hydrides with orientation within 40° or 45° of the radial direction) is the most commonly used metric [6]. The hydride continuity coefficient (HCC) has been used by Canadian researchers to characterize the extent of radial-hydride formation in Zr-2.5%Nb pressure tubes [10,11]. It is determined by projecting the radial hydrides within a 0.11-mm circumferential band onto the radius across the metal wall.…”