Synchrotron analysis of toughness anomalies in nanostructured bainite

High-resolution synchrotron X-ray diffraction has been used to characterise the notch root regions of Charpy impact test specimens of a superbainitic steel, both before and after loading. The changes in the volume fraction of austenite induced by the application of a three-point-bending load were quantified. Analysis of diffraction peak shifts revealed the extent of residual tensile and compressive strains present due to both machining and an applied load. The results lend support to the hypothesis that the comparatively low energies absorbed during Charpy impact testing of superbainitic steels, < 7 J, are due to the formation of stress-induced martensite at the notch root, prior to crack initiation.The authors are grateful to Prakash Srirangam Venkata and Bernard Ennis for their valuable contribution to the synchrotron work; to Diamond Light Source (Oxford) for access to the synchrotron facilities (under experiment EE8564); to Tata Steel UK and the Engineering and Physical Sciences Research Council of the UK for financial support (under EP/H500375/1 and EP/I02249X/1).This is the final version of the article. It was first available from Elsevier via http://dx.doi.org/10.1016/j.actamat.2015.11.02

The association of hydrogen with nanometre bubbles of helium implanted into zirconium

Electron energy-loss spectroscopy (EELS) is used to investigate the association of hydrogen with helium bubbles in zirconium. Conventional EELS data yield a signal at 13.5 eV (similar to the hydrogen K-edge, 13 eV), which is spatially distributed around the peripheries of bubbles and may correlate with the concentration of hydrogen/deuterium in the material. Ultra-high energy resolution EELS yields a signal at 148.6 meV (comparable to a range of ZrH bonds, 130–156 meV) from a region containing bubbles and no visible hydrides. These signals are interpreted in the context of either bubble surface chemisorption or bubble stress field trapping mechanisms