9. Multi-phase thermodynamics and kinetics
In most cases, structural materials are complex multi-component multi-phase materials composed of various different alloying components. Their distinct mechanical, technological and thermo-physical properties are a consequence of their microstructure, which can be controlled by sequences of thermal, mechanical and thermo-mechanical treatments. Research focus of the materials technology group is the computational description of dynamic and static materials behavior as given by the evolution and constitution of the materials microstructure. The target materials of this research are binary and ternary model alloys to study the basics of phase transitions as well as complex technical materials with often up to 10-12 alloying elements.
In research and development of advanced structural materials, a combination of excellent strength and good toughness is usually desired. One of the most important strengthening mechanisms in advanced materials is precipitation strengthening caused by a fine dispersion of second-phase particles. In March 2008, when Ernst Kozeschnik joined the Faculty of Mechanical and Industrial Engineering as Professor of Materials Technology, he looked back on 15 years of experience in modeling and simulation of equilibrium and non-equilibrium thermodynamics as well as phase transformation kinetics. In the last 7 years, together with colleagues from Leoben University and Academy of Sciences of the Czech Republic, he was actively involved in development of novel approaches to simulation of nucleation and growth of precipitates in complex alloying systems. In 2004, he published first versions of the software MatCalc (http://www.matcalc.at), which has nowbecome one of the most versatile and powerful tools for computer simulation of precipitation during thermo-mechanical treatment of complex materials. More recent scientific activities of the materials technology group are focussed towards the description of the birth process of precipitates, that is nucleation.
Since 2007, a Christian Doppler Laboratory for Early Stages of Precipitation has been installed, where precipitation processes in micro-alloyed steel, tool steels, refractory metals as well as Ni-base alloys are investigated. A particular challenge in this context is the fact that nucleation and growth processes span multiple space and time scales. Nucleation typically occurs on the atomic level on sub-nanometer length scale within milliseconds, seconds or years. Further evolution of the precipitates, that is growth and coarsening, continue on mesoscale with spatial dimensions in the order of micrometers and millimeters. In many cases, these processes have to be followed over minutes, hours, years and even decades of real time, such as, for instance, during creep loading of hightemperature creep-resistant materials.
Traditionallly, the main focus of the materials technology group is on continuum modelling of nucleation, growth and coarsening of precipitates. However, the need for extended physical understanding of the mechanism and for achieving more predictive computational modelling capability has lead to increasing implementation of atomistic modeling techniques (Monte Carlo, Kinetic Monte Carlo and Cluster Dynamics Simulation) into the research activities of the materials technology group. These techniques are characterized by strong connections to electronic structure calculations based on, e.g., Density Functional Theory. A corresponding existing cooperation with University of Vienna (Raimund Podloucky) is funded by FWF and deals with bcc Cu and ordered NiAl precipitation in a-Fe. First contacts have already been made with the TU groups of Peter Mohn and Josef Redinger, which are planned to be intensified. Further possibilities of cooperation with mathematics groups or, for instance, Helmut Boehm’s group will be explored in the near future.