On Tuesday afternoon we listened to in-depth presentations from Pavel Korzhavui, Mikhail Dzugutov and Anatoly Belonoshko of examples of their work in ab-initio and molecular dynamics.
We also reviewed the status of the four graduate student projects. Since these are the main topic at our monthly meetings we were rather brief here. A short summary is as follows:
Erik von Schwerin (NADA) has started to do molecular dynamics. The first aim is to set up a generic solidification process. This can be used for instance to deduce properties of stochastic noise, as is needed in phase fields.
Walter Villanueva can now do wetting problems with two immiscible liquids, using Cahn-Hilliard and Navier-Stokes equations in two and three dimensions. Some aspects of liquid phase sintering can be studied with this, and a paper is to be written.
Klara Asp can now do three-phase phasefield simulations of solid-state transformations with realistic properties, showing coarsening, pinch-off, three phase contact points etc. A paper is being written.
Elin Olsson has completed a study of a novel free boundary method, applied to droplet motions in liquids. This method is conceptually between phase fields and levelsets, with much better conservation properties than typical levelset methods. A paper is being reviewed by J Comp Physics.
One next step overall is to join the experience gained so far to be able to do reactive wetting problems involving liquid, solid and gas/void. Most of the tools for doing this are now available to us, as seen from the list above. Special attention has to be paid to the motion of solid particles though.
On Wednesday morning we formed three groups that discussed separately. The topics were taken from a list that had first been identified as:
The three groups were (reporting chairman of each group is underlined):
Erik von Schwerin
John Ågren reported that his group had discussed rigid body motion in phase fields and nano-micro coupling. The rigid body motions in phase field models are known to be complicated due to the importance of internal stresses in the solid that are not possible to treat with explicit numerical schemes, as is standard in the phase field community. Gustav Amberg has done some preliminary work on this and has some ideas. A meeting was set with John, Gustav, Klara and Walter, to plan how to proceed.
The group also discussed in detail about possible problems where a coupling between nano- and micro-scales would be truly crucial. Such are stacking faults and vacancies in irradiated materials; formation of clusters in alloys. Also non-smooth phase interface features, such as tips of Widmanstätten plates, that are probably atomistically sharp, would present a true interplay between long range diffusion and atomistic processes at the tip. An obvious possibility is also to use ab-inito and/or MD to obtain free energies and material properties that are needed in phase field modeling at longer length scales.
Gunilla Kreiss and group had discussed nano-micro coupling and wetting phenomena. In phase fields, there is a need for diffusion coefficients, interface energies, etc. There is also a need for mobilities and diffusion coefficients in the interface region. These are difficult to measure experimentally, but could be obtained using molecular dynamics. Erik (von Schwerin) is already starting to do phase change with MD, and his computations could be used to obtain this information.
Wetting problems were also discussed. Here information about surface energies etc are also needed, that can in principle be obtained from MD etc. Such computations could be quite heavy though and when reasonable, ad-hoc arguments could be used. Qualitative information is also important, and can be much cheaper.
Bosse Jansson described a few observations and phenomena from sintering of hard materials, for instance that when joining WC (tungsten carbide) and TiC (titanium carbide), the Co (Cobalt) binder phase will be adsorbed into the TiC, from the WC. Such phenomena could be studied using the wetting modeling available to us now.
Anders Szepessy reported discussions that had touched upon wetting problems, but had spent most of the time on the contact with industrial applications. Bosse Jansson contributed in particular to the discussion of industrial applications: From the industry’s point of view, academic projects that are worthwhile to participate in should do things that the industry is not doing itself. This project is aimed at methods for studying/developing materials, and there is knowledge accumulated and developed that does not exist in industry. It is thus the right project to be involved in.
Anders Szepessy is involved in an EU proposal for pre- and postdoc training. This is due in December and could typically fund postdocs from other members of the network in the proposal. The proposal needs to be interdisciplinary and intersectorial. This was discussed and various possible contacts were identified. Our project will enter as a partner in the application.
Finally we called upon our two external members to comment on what they see as our strength/weakness, our possibilities etc.
Bo Jansson: Some things were mentioned above, notably that from the industry’s point of view, academic projects that are worthwhile should do things that the industry is not doing itself. This project is aimed at methods for studying/developing materials, and there is knowledge accumulated and developed that does not exist in industry, which makes it relevant for the industry. There has been a worrying trend in that there has been increased pressure to find funding from industry of academe that wants to do product development. This is best done in industry, and this center has the right attitude in that it develops knowledge that is not available in industry.
It is fascinating to see for instance the wetting simulations. Practical issues are how to choose powder size distributions etc, in the presence of coarsening, in order to have good consolidation.
It is interesting that this group is now, using computers, beginning to address questions that have been waiting a long time to be answered.
Per Lötstedt: This project has an interesting mix of people from different areas. The participants seem to understand each other. This has been a problem in other similar projects that he has been involved in. The different sub-projects show a variety, but there is also collaboration. We should make sure that the publications that start to come out also show that there is collaboration. He does not see any specific dangers or threats, rather a bright future.