The Minisymposium "Materials design and application based on thermodynamics and phase diagrams" will take place on Friday, May 16th between 2 - 5 pm in SR2 of the Faculty of Chemistry.
Prof. Dr. Martin Heilmaier, Institute of Technology, Karlsruhe
"Thermodynamics guided development of novel high temperature oxidation resistent refractory alloys"
We will review the status of our current high temperature structural materials development based on refractory metals. For obtaining appropriate high temperature creep and corrosion properties multi-phase microstructures are demanded. We will show how thermodynamics predictions can guide us to fulfill these requirements with two case studies for which ternary sections are available: (1) the Mo-Si-Ti system and (2) the Cr-Mo-Si system, both exhibiting solidus temperatures far beyond those of currently used Ni-base superalloys. A short outlook towards multi-phase refractory high entropy (i.e. compositionally complex) alloys will conclude the presentation.
Dr. Mario Kriegel, TU Bergakademie Freiberg
"CalPhaD-Assissted Alloy Design for Fe-based Shape Memory Alloys"
Shape-memory alloys (SMAs) based on the Fe–Mn–Al–Ni system provide promising advantages over conventional NiTi-based alloys in terms of materials costs and cold workability. To understand energetic contributions of the intermetallic B2 precipitates to the parent phase in order to initiate the martensitic transformation, thermodynamic calculations were performed using a quaternary Al–Fe–Mn–Ni CalPhaD (Calculation of Phase Diagrams) database. With the aid of extrapolated T0 temperatures for the B2 precipitates and energetic considerations (EAM potentials) of the differences between B2 and L10, both adopted from literature data, the thermodynamic stability of the B2 phase was approximated. In order to verify the applicability of thermodynamic calculations for a target-oriented alloy design of Fe-based SMAs, several samples with varying fractions of B2 particles and different stabilities against the martensitic transformation were prepared, annealed, subsequently tested using nanoindentation and analyzed using electron-backscatter diffraction (EBSD). In order to describe the deformation behavior and to assess the reversibility of the martensitic transformation upon loading and unloading, the work-recovery ratio was determined from indentation curves. Since the martensitic transformation behavior is strongly dependent on the crystal orientation, the nanoindentation and EBSD measurements were performed on numerous differently oriented grains. It is shown that the volume fraction and the stability of the intermetallic B2 precipitates against the transformation towards an L10-like state severely influence the overall stability of the parent state in Fe–Mn–Al–Ni SMAs and consequently, the reversibility of the martensitic transformation.