Large Deformation Processes in Lamellar Structures

Materials with a lamellar microstructure, like lamellar composites, are well known to the technical community. However, such microstructures may develop in nature without any lamination process. A prominent representative is the pearlite in the case of steels. One of the most amazing materials of the near future are Titanium-Aluminium Intermetallics (Ti-Al). They solidify during casting processes in very accurate lamellar structures with two types of layers showing different physical and mechanical behaviour. Some of the astonishing properties of Ti-Al are its weight (half that of superalloys), its oxidation resistance and its superior creep resistance at high temperatures. However, one of the preconditions for the use such a material in technical applications, generally involving some high-temperature environment, is that the coarse as-cast material must be refined and homogenized by a deformation process to achieve the necessary ductility and strength. The crucial question arising here is how to deform such a lamellar material to an amount of 80 % and more. Artificially produced lamellar composites are never subjected to such a high compressive deformation. Therefore, almost no practical or theoretical experience has been gathered in the past. Two main phenomena can be observed: - The lamellae seem to buckle and form a kinked microstructure as it would appear in the case of compression of a pack of playing cards. - Near the kink regions the material rebuilds by recrystallization, a thermodynamically driven process which would not happen in the case of artificial composites. The main goal of the project is to simulate the deformation process in direct relation with local energy concentrations in the kink regions. The local energy balance and its dissipation will be the key to the growth of the new grains by recrystallization. The project can be considered as an interdisciplinary project combining continuum mechanics and metal physics (which may be seen as Materials Mechanics). The project will performed together with a leading group in Ti-Al research and production.