In situ study of sigma phase formation in Cr-Co-Ni ternary alloys at 800°C using the long duration experiment facility at Diamond Light Source.

The new long duration experiment facility on beamline I11 at Diamond Light Source has been used to study the kinetics of sigma phase formation in three Cr-Co-Ni alloys. Diffraction data acquired during in situ exposure at 800°C for 50 d showed progressive increases in the sigma fraction. This was accompanied by changes in the proportions of the other phases, which differed markedly between the alloys studied. These results demonstrate the capabilities of the long duration facility for the study of metallurgical phenomena over periods of months to years, a capability not previously available at a synchrotron source

The effect of phase chemistry on the extent of strengthening mechanisms in model Ni-Cr-Al-Ti-Mo based superalloys

The exceptional mechanical properties of polycrystalline nickel-based superalloys arise through various concurrent strengthening mechanisms. Whilst these mechanisms are generally understood, consensus has yet to be established on the precise contribution of each to the overall alloy strength. Furthermore, changes in alloy chemistry influence several different mechanisms, making the assessment of individual alloying elements complex. In this study, a series of model quinary Ni-based superalloys has been investigated to systematically study the effect of varying Mo content on the contributing strengthening mechanisms. Using microstructural data, the yield strength was modelled by summing the individual effects of solid solution in both the γ and γ ' phases, coherency, grain boundary and precipitation strengthening. The total predicted yield stress increased with Mo content despite the diminishing contribution of precipitation strengthening. It is shown that solid solution strengthening of the ordered γ' precipitate phase is a key contributor to the overall strength, and that variations in composition between the tertiary and secondary γ ' lead to significant changes in mechanical properties that should be accounted for in models of alloy strength.Funding was provided by the EPSRC/Rolls-Royce Strategic Partnership under EP/M005607/1 and EP/H022309/1. The Oxford Atom Probe facility was funded by the EPSRC under EP/M022803/1. E. I. Galindo-Nava would like to acknowledge the Royal Academy of Engineering for his fellowship funding. Neutron diffraction beam time was supported through the Canadian Neutron Beam Centre under Experiment number 1258

Adiposity, fitness, health-related quality of life and the reallocation of time between children’s school day activity behaviours: a compositional data analysis

Sedentary time (ST), light (LPA), and moderate-to-vigorous physical activity (MVPA) constitute the range of school day activity behaviours. This study investigated whether the composition of school activity behaviours was associated with health indicators, and the predicted changes in health when time was reallocated between activity behaviours. Accelerometers were worn for 7-days between October and December 2010 by 318 UK children aged 10-11, to provide estimates of school day ST, LPA, and MVPA. BMI z-scores and percent waist-to-height ratio were calculated as indicators of adiposity. Cardiorespiratory fitness (CRF) was assessed using the 20-m Shuttle Run Test. The PedsQLTM questionnaire was completed to assess psychosocial and physical health-related quality of life (HRQL). Log-ratio multiple linear regression models predicted health indicators for the mean school day activity composition, and for new compositions where fixed durations of time were reallocated from one activity behaviour to another, while the remaining behaviours were unchanged. The school day activity composition significantly predicted adiposity and CRF (p=0.04-0.002), but not HRQL. Replacing MVPA with ST or LPA around the mean activity composition predicted higher adiposity and lower CRF. When ST or LPA were substituted with MVPA, the relationships with adiposity and CRF were asymmetrical with favourable, but smaller predicted changes in adiposity and CRF than when MVPA was replaced. Predicted changes in HRQL were negligible. The school day activity composition significantly predicted adiposity and CRF but not HRQL. Reallocating time from ST and LPA to MVPA is advocated through comprehensive school physical activity promotion approaches

HIRDLS poster

A poster supporting the HIRDLS data held at the BADC (High Resolution Dynamics Limb Sounder (HIRDLS) instrument)

Dynamical and chemical evolution of gas-rich dwarf galaxies

We study the effect of a single, instantaneous starburst on the dynamical and chemical evolution of a gas-rich dwarf galaxy, whose potential well is dominated by a dark matter halo. We follow the dynamical and chemical evolution of the ISM by means of an improved 2-D hydrodynamical code coupled with detailed chemical yields originating from type II SNe, type Ia SNe and single low and intermediate mass stars (IMS). In particular we follow the evolution of the abundances of H, He, C, N, O, Mg, Si and Fe. We find that for a galaxy resembling IZw18, a galactic wind develops as a consequence of the starburst and it carries out of the galaxy mostly the metal-enriched gas. In addition, we find that different metals are lost differentially in the sense that the elements produced by type Ia SNe are more efficiently lost than others. As a consequence of that we predict larger [$\alpha$/Fe] ratios for the gas inside the galaxy than for the gas leaving the galaxy. A comparison of our predicted abundances of C, N, O and Si in the case of a burst occurring in a primordial gas shows a very good agreement with the observed abundances in IZw18 as long as the burst has an age of $\sim 31$ Myr and IMS produce some primary nitrogen. However, we cannot exclude that a previous burst of star formation had occurred in IZw18 especially if the preenrichment produced by the older burst was lower than $Z=0.01$ Z$_{\odot}$. Finally, at variance with previous studies, we find that most of the metals reside in the cold gas phase already after few Myr. This result is mainly due to the assumed low SNII heating efficiency, and justifies the generally adopted homogeneous and instantaneous mixing of gas in chemical evolution models.Comment: 25 pages, Latex, 18 figures, accepted for publication in MNRA