The roles of Eu during the growth of eutectic Si in Al-Si alloys.

Jiehua Li,Manfred Wiessner,Fredrik Hage,Quentin Ramasse,Lorenz Romaner,Peter Schumacher,Daniel Scheiber,Bernhard Sartory

doi:10.1038/srep13802

Abstract

Controlling the growth of eutectic Si and thereby modifying the eutectic Si from flake-like to fibrous is a key factor in improving the properties of Al-Si alloys. To date, it is generally accepted that the impurity-induced twinning (IIT) mechanism and the twin plane re-entrant edge (TPRE) mechanism as well as poisoning of the TPRE mechanism are valid under certain conditions. However, IIT, TPRE or poisoning of the TPRE mechanism cannot be used to interpret all observations. Here, we report an atomic-scale experimental and theoretical investigation on the roles of Eu during the growth of eutectic Si in Al-Si alloys. Both experimental and theoretical investigations reveal three different roles: (i) the adsorption at the intersection of Si facets, inducing IIT mechanism, (ii) the adsorption at the twin plane re-entrant edge, inducing TPRE mechanism or poisoning of the TPRE mechanism, and (iii) the segregation ahead of the growing Si twins, inducing a solute entrainment within eutectic Si. This investigation not only demonstrates a direct experimental support to the well-accepted poisoning of the TPRE and IIT mechanisms, but also provides a full picture about the roles of Eu atoms during the growth of eutectic Si, including the solute entrainment within eutectic Si.

Highlights

IntroductionAmong the rare earth elements, only Eu can modify eutectic Si to a fibrous morphology[15,16,17] and Eu is more likely to combine with Si atoms, forming Eu-rich clustering[17]
(r/rSi = 1.646) according to the impurity-induced twinning (IIT) mechanism
A comparison of the experimental high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images, and in particular Fig. 2a,b, with density functional theory (DFT)-calculated models is not expected to yield a perfect one-to-one correspondence due to the simplified model considered for the simulations, a moderately good level of agreement was observed with Case 3, Fig. 3b

Summary

Introduction

Among the rare earth elements, only Eu can modify eutectic Si to a fibrous morphology[15,16,17] and Eu is more likely to combine with Si atoms, forming Eu-rich clustering[17] For this latter case in particular, there is still a lack of a detailed investigation on the distribution of Eu atoms within eutectic Si (i.e. at the twin plane re-entrant edge or at the intersection of Si facets and respectively twins). First-principle calculations were performed to elucidate the segregation behaviour of Eu atoms within Si twins and its effect on the Si twinning The aim of this investigation is to provide direct experimental supports to the well-accepted poisoning of the TPRE and IIT mechanisms, and to elucidate other roles of Eu during the growth of eutectic Si, including the solute entrainment within eutectic Si

Methods

Results

Conclusion