First-principle calculations on the Al/L1₂-Al₃Zr heterogeneous nucleation interface

Abstract

The interfacial properties including interfacial energy, work of adhesion and electronic structure of Al(100)/Al₃Zr(100) were calculated by first-principle calculations based on the density functional theory. The seven layered Al(100) slab and nine layered Al₃Zr(100) slab were employed to construct the interface models. And six Al(100)/Al₃Zr(100) interfaces, including Top, Bridge and Center sites for the Al- and AlZr- terminations, were considered to study. The interfaces with center site stacking of both terminations are the most stable as they have the largest adhesion work (W_ad). The interfacial bonding characteristics is a combination of covalent and metallic bond for the AlZr-terminated center site interface, but only metallic for the Al-terminated center one. Under the whole range of ${\mu }_{Zr}^{slab}-{\mu }_{Zr}^{bulk}$, the interfacial energy of AlZr-terminated center interface is negative, which is much smaller than that of α-Al and its melt (0.15J/m²), indicating that Al₃Zr particle is an effective nucleant for α-Al primary grains.

Introduction

Due to the good thermal and electrical conductivities, low density, and corrosion resistance, Al and its alloys have been widely applied in many industries such as engineering materials for structural applications [1]. The fine grains play a key role in improving the soundness and mechanical properties of Al alloy castings [2,3]. During the solidification processes, adding grain refiner or solute is still the most common method to obtain the refined grain structure. By the addition of Zr, the effective refinement of Al alloys was found [4]. As is known, the Al₃Zr with D0₂₃ structure is the most stable, whereas L1₂ structure is metastable [5]. By the addition of Cu and Ni atoms, the L1₂-Al₃Zr can exist stably at temperatures over 900 °C for Cu and 850 °C for Ni [6]. In the Al-X-Zr(X = Cu, Ni) alloys, the solidification process begins with the formation of L1₂-Al₃Zr phase, and is then followed by the heterogeneous nucleation of α-Al on the L1₂-Al₃Zr, and the lattice match of (100)_Al[010]_Al||(100)_Al3Zr-L12 [010]_Al3Zr-L12 has also been reported [7].

All the abovementioned investigations could not reveal whether L1₂-Al₃Zr is an effective grain refiner, since the atomic interaction between the Al and L1₂-Al₃Zr interface was not considered in these studies. The interfacial properties, such as the interfacial energy, work of adhesion and electronic structure can reflect the nucleation potency between the nucleating crystal and the substrate [2,3]. Unfortunately, even the simplest solid-solid interfacial energy is unavailable yet, due to the difficulties in the experimental studies. Therefore, it is of great significance to investigate the interfacial properties at atomic scale by theoretical calculations in order to identify the possibility of L1₂-Al₃Zr as a heterogeneous nucleation substrate of α-Al.

First-principle calculation can provide the quantitative information for the solid-solid interface at atomic and electronic levels, and it is therefore the best choice to study the nucleation ability of a potent heterogeneous substrate [8]. Recently, calculations on the Al/Al₃Ti [9], Al/NbB₂ [10], Al/Al₃Nb [11], and Al/TiB₂ [12] interfaces were reported, and the respective optimal atomic stacking at the interface were determined. However, until now, there is still no information about the Al/Al₃Zr interfacial properties, such as the atomic stacking, adhesion work, interfacial energy and the electronic structure of the interface. Therefore, it is necessary to make these clear to help us understand the heterogeneous nucleation mechanism.

In this paper, we focus on the Al(100)/L1₂-Al₃Zr(100) interface, since Al(100) and L1₂-Al₃Zr(100) are low indexed planes with a small lattice mismatch. The paper is arranged as follows: we describe the computational details in Section 2; the bulk and surface properties were calculated and discussed in Section 3; In section 4, the results of the interface were presented. Finally, the conclusions were given in Section 5.