No abstract

No abstract

We demonstrate experimentally that a part-per-million addition of Sn solutes in Al-Mg-Si alloys can inhibit natural aging and enhance artificial aging. The mechanism controlling the aging is argued to be vacancy diffusion, with solutes trapping vacancies at low temperature and releasing them at elevated temperature, which is supported by a thermodynamic model and first-principles computations of Sn-vacancy binding. This "diffusion on demand" solves the long-standing problem of detrimental natural aging in Al-Mg-Si alloys, which is of great scientific and industrial importance. Moreover, the mechanism of controlled buffering and release of excess vacancies is generally applicable to modulate diffusion in other metallic systems.

No abstract

This study presents a design strategy for Al-Mg-Si alloys to control natural aging. Recently, trace addition of Sn was shown to suppress natural aging for up to two weeks, which was explained by the strong trapping of vacancies to Sn atoms. Here we explore the effect of Keywords: aluminum alloys, natural aging, phase transformation kinetics, vacancies, trace elements This is a pre-print of the following article: Werinos, M.; Antrekowitsch, H.; Ebner, T.; Prillhofer, R.; Curtin, W. A.; Uggowitzer, P. J.; Pogatscher, S. Acta Mater. 2016, 118, 296-305.. The formal publication is available at http://dx

In this study, we describe the effect of the main alloying elements Ni, Cu and Mg on the mechanical properties of near eutectic and hypoeutectic Al-Si foundry alloys at 250uC after a long term exposure to test temperature. Systematic compositional variations illustrate the significant hardening effect of secondary precipitates such as Al 2 Cu and Mg 2 Si. It is also shown that the strength is increased by the addition of Ni, albeit only to a certain level, depending on the fraction of eutectic phase in the alloy. The alloys are considered as coarse two-phase systems, where a hardening effect is caused by load transfer to the harder phase, which requires a certain contiguity of the latter. This paper discusses the individual influences of Ni, Cu and Mg on the high temperature strength and describes a potentially adverse effect of the combinations Cu/Ni and Cu/Mg.

No abstract

Hospitalized children who undergo painful procedures are more susceptible than others to experiencing iatrogenic effects, such as anxiety, pain, and severe stress. Clowns in clinical setting have been found to be effective in reducing children's experiences of these effects during hospitalization and before procedures. This article provides an overview of clowning in health care settings; reviews major studies conducted on clowning for hospitalized children, discussing evidence that clown interventions decrease pain and distress in pediatric patients; and concludes with a discussion of health care clowning as a profession.