Grain refinement of Al-Mg-Sc alloy by ultrasonic treatment

In foundry practice, ultrasonic treatment has been used as an efficient technique to achieve grain refinement in aluminium and magnesium alloys. This article shows the strong effect of pouring temperature and ultrasonic treatment at various temperatures on the grain refinement of Al-1 wt% Mg-0.3 wt% Sc alloy. Without ultrasonic treatment, a fine grain structure was obtained at the pouring temperature of 700 °C. The average grain size sharply decreases from 487 ± 20 to 103 ± 2 μm when the pouring temperature decreases from 800 to 700 °C. Ultrasonic vibration proved to be a potential grain refinement technique with a wide range of pouring tem- perature. A microstructure with very fine and homogeneous grains was obtained by applying ultrasonic treatment to the melt at the temperature range between 700 and 740 °C, before pouring. Cavitation-enhanced hetero- geneous nucleation is the mechanism proposed to explain grain refinement by ultrasound in this alloy. Moreover, ultrasonic treatment of the melt was found to lead to cast samples with hardness values similar to those obtained in samples submitted to precipitation hardening, suggesting that ultrasonic treatment can avoid carrying out heat treatment of cast parts.This research was supported by The Project Bridging The Gap, funded by the Erasmus Mundus External Cooperation Window Programme. Acknowledgements also to the University of Minho, for the provision of research facilities

Growth of Ru and RuO2 films by metal-organic chemical vapour deposition

We have prepared RuO2 layers by metal organic chemical vapour deposition using liquid delivery source and by thermal evaporation of powder precursors. The films were prepared on silicon and r-plane cut sapphire substrates. We discuss thermodynamics of both types of MOCVD techniques. Liquid delivery source technique using diglyme solvent results in deposition of metallic Ru film with some traces of RuO2, while films prepared by thermal evaporation of powder precursors consist of pure RuO2 phase. Thermal evaporation MOCVD grown RuO2 films exhibit excellent electrical properties ; room temperature resistivity of 30 µΩ.cm and residual resistivity ratio between 8 and 30

Effect of cooling rates on the properties of Portland cement clinkers in the presence of Mg

In order to enhance the performance of Portland cement clinker, this study investigates the effect of cooling rates on the mineralogical composition of cement clinkers containing magnesium (Mg), which is the most common minor element in raw materials (e.g., limestone). Three cooling regimes were considered to simulate industrial kiln processing conditions. MgO contents of 0, 3, and 6 wt.% were considered in this study. After synthesis of the clinkers, quantitative X-ray diffraction is used to investigate the mineralogical composition, as well, the phase amounts using the Rietveld method. The results show that rapid cooling and Mg doping can promote the formation of alite, and monoclinic alite can be stabilized via Mg ions. Slow cooling and Mg incorporation can stabilize g- C2S, but a rapid cooling rate is still effective to restrain the transformation from b-C2S to g-C2S in MgO-doped clinker. The cooling rates do not influence the content of ferrite and C3A obviously, but the MgO incorporation can enhance the ferrite formation and reduce the C3A content. At a slow cooling rate, little Mg can dissolve in clinker phases, but the retention of MgO in clinker phases can be increased by a fast cooling rate. Therefore, the effect of MgO on the mineralization and the solubility of MgO is a function of cooling rates