2015 Van Horn Distinguished Lectures: 2
2,701 views · Published 15 May 2015 · 1:05:13 · Indexed 24 October 2026
Channel: bhadeshia123 · 2015 · Education
The Kent R. van Horn Lectureship is an endowed Lectureship at the Case Western Reserve University and dates from 1974. It honours Kent R. van Horn, an alum, who had a distinguished career as a metallurgist, director of research, and ultimately corporate vice-president of Alcoa. Three lectures on varied topics are to be delivered over three successive days. The 2015 lectures were delivered by Professor Harry Bhadeshia. This one is about the evolution of solutions. These videos are reproduced courtesy of the Materials Science and Engineering Department of Case Western Reserve University. http://engineering.case.edu/emse/node/121 http://www.phase-trans.msm.cam.ac.uk Abstract: In ordinary life, we take it for granted that when sugar is added to tea, it will form a solution. In academia, we understand solid solutions that form by mixing elements in the liquid state followed by solidification. Less well understood is the process where solid particles of different composition are mixed together by mechanical alloying until they form an intimate solution that can be probed on an atomic level. In this lecture, I address this issue from the point of view of materials destined for fusion reactors or where they must resist severe oxidation and creep. Some discoveries are made in the process, that defy intuition and resolve some long-standing problems in thermodynamics and nucleation. Here goes. Normal thermodynamic theory for solutions begins with the mixing of component atoms. Many solutions are, however, prepared by mixing together lumps of the components, each of which might contain millions of identical atoms. We examine here the way in which a solution evolves from these large clusters of components, from a purely thermodynamic point of view. There are some interesting results including the prediction that solution formation by the mechanical alloying of solid components cannot occur unless there is a gain in coherency as the particles become small. The nature of the barrier to mechanical alloying is discovered. There is also the possibility of a metastable state prior to the achievement of full solution, when the component atoms prefer like neighbours.
