Nucleation Of Eutectic Si Research Articles

Generation of a Uniformly Coarse Two-Phase Microstructure in a Hypereutectic Ag-Si Alloy

Abstract Wetting experiments require a uniform coarse two-phase microstructure with microstructural constituents in an order of magnitude of ∼200 μm. Such a microstructure was generated using a hypereutectic Ag-Si alloy (Ag-10wt.%Si). It was adjusted by relatively slow cooling to a temperature close to the eutectic temperature, by coarsening the primary Si phase in the two-phase liquid/solid mixture, and, eventually, by very slow cooling below the eutectic temperature. Nucleation of eutectic Si is inhibited by the low cooling rate and by rotating the sample. The rotation also prevents the occurrence of gravity segregations (floating of primary-Si).

The interaction between Eu and P in high purity Al-7Si alloys

The interaction between Eu and P in high purity Al-7Si alloys was investigated. Interrupted solidification experiments were undertaken to study macrostructure evaluation and thermal analyses were performed to obtain characteristic temperatures of the eutectic reaction. Without the presence of Eu, increasing P concentrations results in a significant increase in the number of eutectic grains due to the formation of AlP particles, which can act as nucleation sites for eutectic Si. With the presence of Eu, a decrease in nucleation frequency and thereby an increase in eutectic grain size was observed in alloys containing 5 and 30ppm P due to the interaction between Eu and P, which can be further supported by the results of μ-XRD patterns and SADP of TEM. It was found that most P-rich particles were covered by Eu-rich intermetallics, which are indexed to be Al2Si2Eu phase, indicating that the formation of the pre-eutectic Al2Si2Eu phase may lead to a depletion of pre-existing AlP particles or residual P in the melt. This investigation highlights the effect of the interaction between Eu and P on the nucleation of eutectic Si and eutectic grains.

Nucleation and Growth of Eutectic Si in Al-Si Alloys with Na Addition

Al-5 wt pct Si-based alloys with Na additions (19 and 160 ppm) have been produced by controlled sand casting and melt spinning. Entrained droplet technique and differential scanning calorimetry were employed to investigate the nucleation behavior of eutectic Si. High-resolution transmission electron microscopy and atom probe tomography were used to investigate the distribution of Na atoms within eutectic Si and at the interfaces between eutectic Si and eutectic Al. It was found that (i) only 19 ppm Na addition results into a high undercooling (49 K (49 °C)) of the entrained eutectic droplet. However, further increasing Na addition up to 160 ppm exerts no positive effect on the nucleation of eutectic Si, instead a decreased undercooling (29 K (29 °C)) was observed. (ii) Na addition suppresses the growth of eutectic Si due to the Na segregation at the interface between eutectic Si and eutectic Al, and (iii) Na addition promotes significant multiple Si twins, which can be attributed to the proposed adsorption of Na atoms at the intersection of Si twins and along the 〈112〉Si growth direction of Si. The present investigation demonstrates, for the first time, a direct observation on the distribution of Na atoms within eutectic Si and thereby provides strong experimental supports to the well-accepted impurity-induced twinning growth mechanism and poisoning of the twin plane re-entrant edge growth mechanism.

Fourier thermal analysis of the solidification kinetics in A356/SiCp cast composites

The aim of this work was to explore the effect of the presence of SiCp on the solidification kinetics and the microstructural characteristics of A356/SiCp cast composites by using the Fourier thermal analysis (FTA) method. The tests were performed in order to identify changes in the solidification kinetics of the metal matrix that could be caused by the presence of particle reinforcement. FTA results were complemented with information provided by microstructural characterisation. The outcome of this work suggests that the presence of SiCp affect the solidification kinetics of both the primary dendritic phase and the eutectic microconstituent. These effects are apparently due to two main causes: (1) the decrease of the latent heat released during solidification associated to the presence of SiCp and (2) the change in the growth kinetics and morphology of the eutectic present in the metal matrix alloy produced by the nucleation of eutectic Si on SiCp.

Fourier thermal analysis of the solidification kinetics in A356/SiCp cast composites

The aim of this work was to explore the effect of the presence of SiC p on the solidification kinetics and the microstructural characteristics of A356/SiC p cast composites by using the Fourier thermal analysis (FTA) method. The tests were performed in order to identify changes in the solidification kinetics of the metal matrix that could be caused by the presence of particle reinforcement. FTA results were complemented with information provided by microstructural characterisation. The outcome of this work suggests that the presence of SiC p affect the solidification kinetics of both the primary dendritic phase and the eutectic microconstituent. These effects are apparently due to two main causes: (1) the decrease of the latent heat released during solidification associated to the presence of SiC p and (2) the change in the growth kinetics and morphology of the eutectic present in the metal matrix alloy produced by the nucleation of eutectic Si on SiC p .