A New Atomistic Mechanism for Heterogeneous Nucleation in the Systems with Negative Lattice Misfit: Creating a 2DTemplate for Crystal Growth

• Main Authors: Zhongyun Fan, Hua Men, Yun Wang, Zhongping Que
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Metals
• Subjects: heterogeneous nucleation; MD simulation; solidification; interface
• Online Access: https://www.mdpi.com/2075-4701/11/3/478

Heterogeneous nucleation is a widespread phenomenon in both nature and technology. However, our current understanding is largely confined to the classical nucleation theory (CNT) postulated over a century ago, in which heterogeneous nucleation occurs stochastically to form a spherical cap facilitated by a substrate. In this paper, we show that heterogeneous nucleation in systems with negative lattice misfit completes deterministically within three atomic layers by structural templating to form a two-dimentional template from which the new phase can grow. Using molecular dynamics (MD) simulations of a generic system containing metallic liquid (Al) and a substrate of variable lattice misfit (fcc lattice with fixed Al atoms), we found that heterogeneous nucleation proceeds layer-by-layer: the first layer accommodates misfit through a partial edge dislocation network; the second layer twists an angle through a partial screw dislocation network to reduce lattice distortion; and the third layer creates a crystal plane of the solid (the 2D nucleus) that templates further growth. The twist angle of the solid relative to the substrate as a signature of heterogeneous nucleation in the systems with negative lattice misfit has been validated by high resolution transmission electron microscopic (HRTEM) examination of TiB₂/Al and TiB₂/<i>α</i>-Al₁₅(Fe, Mn)₃Si₂ interfaces in two different Al-alloys.