4th International Conference on Advances in Solidification Processes
8-11th July 2014, Beaumont Estates, Old Windsor, UK

Prof Zhongyn Fan - Brunel University

Zhongyun Fan
Professor Fan is currently a Professor of Metallurgy and the Founder and current Director of BCAST (Brunel Centre for Advanced Solidification Technology) at Brunel University, Uxbridge, UK. He is the principal investigator/director of the EPSRC Centre – LiME (total funding £11.5M), a national centre of excellence in liquid metal engineering, and also is the principal investigator of the EPSRC funded national programme TARF-LCV (total funding £4.5M). He obtained his first degree in Metallurgy from University of Science and Technology Beijing and his PhD in Materials Science and Engineering from Surry University. He started his academic career in 1997 at Brunel University, and prior to this he was a research fellow at Oxford University and Surrey University. He has published over 300 scientific papers with an H-Index of 30. He was the recipient of the Elegant Work Prize (1995), the Cook/Ablett Award (2003) and Dowding Medal and Prize (2012) of the Institute of Materials, Minerals and Mining (IOM3) and the Corac Research Award (2003) of Brunel University, , Diploma Award (2012) of the Institute of Cast Metals Engineers (ICME). Professor Fan is the principal inventor of twin-screw and rotor-stator based high shear processes, and holds 3 international patents and 6 UK patents. He is a co-chairman of the Casting and Solidification Society of IOM3, a Fellow of IOM3 (FIMMM), a Fellow of ICME (FICME), and a member of the scientific committee of 6 international conferences on solidification and solidification processing. Professor Fan’s current research interest covers solidification processing of metallic materials, heterogeneous nucleation and alloy development.

Abstract

Recent advances in the understanding of heterogeneous nucleation

Z. Fan

BCAST, Brunel University, UK

Solidification starts with nucleation followed by growth. 60 years of extensive solidification research has significantly improved our understanding of crystal growth, but made little progress in understanding of nucleation beyond the classical nucleation theory (CNT). Due to the fact that it is almost impossible to observe the nucleus in metallic, molecular or ionic systems, most of our current knowledge of nucleation comes from simulation of homogeneous nucleation in very simple systems, while the limited experimental work is exclusively on heterogeneous nucleation in more complex systems. However, the recent advances in high resolution electron microscopy and advanced computational techniques have provided us with great opportunities to investigate heterogeneous nucleation at the atomic level. With the financial support from the EPSRC (Engineering and Physical Sciences Research Council, UK) under the LiME grant, we have made good progress in understanding heterogeneous nucleation during solidification of metallic materials. In this lecture I will provide an overview of our latest progress in understanding heterogeneous nucleation achieved in the last few years. This will include:

  • Pre-nucleation phenomenon: substrate induced atomic ordering at the liquid/substrate interface. We found that a crystalline substrate can induce substantial ordering at the liquid/substrate interface at temperatures above the liquidus. We also found that pre-nucleation is promoted by reducing the misfit between the substrate and the nucleating phase.
  • An epitaxial nucleation model: heterogeneous nucleation on potent substrates (i.e., with small lattice mismatch with the nucleating phase) occurs via layer-by-layer growth. Due to the presence of pre-nucleation, there is neither energy barrier nor hysteresis for epitaxial nucleation.
  • Manipulation of heterogeneous nucleation: adsorption of solute/impurity atoms at the liquid/substrate interface to either enhance or poison heterogeneous nucleation. A solute (or impurity) element may segregate to the liquid/substrate interface through adsorption, forming a 2D compound or 2D solution, which in turn can either promote nucleation by reducing the lattice misfit or poisoning by increasing the lattice misfit or denying pre-nucleation.
  • Competition between different types of substrates: potency vs efficiency for grain refinement. For effective grain refinement the nucleating particles need to be potent (smaller misfit), of sufficient number density, of suitable size and size distribution. Potent particles with insufficient number density may lead to coarsening, while a sufficient number of particles with large misfit may lead to significant grain refinement if there are no other particles present in the liquid.
  • Classical nucleation theory (CNT) vs non-classical nucleation theory (NCNT).