Heterogeneous nucleation and microstructure formation: Steps towards a system and scale bridging understanding

Abstract

For 6 years from 2007–2013 the DFG has funded the scientific priority program 1296 with the above title. Its aim was to attain a fundamental understanding of the basic mechanisms underlying heterogeneous nucleation as well as the subsequent development of the nucleus into a specific heterogeneous microstructure. To that end a system- and method-spanning scientific approach was developed, in which the simplest types of model systems for heterogeneous crystalline orders, for pure metals, binary metal alloys, and colloids, were investigated in a comparative manner. Moreover they were assessed with complementary experimental as well as simulation techniques from the atomic to the mesoscale to obtain a comprehensive view across all relevant time and length scales, as depicted in Fig. 1. The figure illustrates the key idea of the priority program, namely to exploit a smearing of scales as given by the two complementary material systems for a most comprehensive assessment of the diverse kinetic, energetic and morphological features involved in heterogenous nucleation. Some of the questions explored in detail in the context of the priority program are summarized in the following: – Heterogeneous nucleation: What does a critical nucleation grain look like? Does the classical concept of a contact angle make sense for heterogeneous nucleation? Can claims be made about the dominant contributions to the nucleation barrier for heterogeneous nucleation, like they can be obtained from molecular simulations, During the course of the priority program one of its members, Prof. Dr. R. Bormann, died in a tragic accident. In his scientific work R. Bormann pushed with full enthusiasm particularly fundamental problems related to the phase transformation in metallic alloys, as they were also a central focus of this priority program. He supported the priority program from its initial stages: first as project leader, later he became president of University of Bayreuth. In that role he took responsibility in particular for fostering the frame for interdisciplinary scientific activities – a second link to the efforts and achievements in this priority program. We dedicate this overview article on the work in the priority program 1296 to the enthusiasm with which he engaged himself for both roles.