Functionally graded structures from high manganese iron based alloys - From TWIP effect to superelasticity

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Current alloys and processes have to meet challenging requirements. In the light of resource efficiency light-weight design is of utmost relevance. For this reason materials of high specific strength are numerously employed. Tailoring of local properties allows for a further improvement of the light-weight potential of these high performance alloys. It is possible to tailor local material properties in such way that the requirements set by the local loading situation are perfectly accomplished. This can be obtained by manipulation of geometry, microstructure and chemical composition. Not only strength and ductility can be affected, functionalization of the material is possible as well. The latter can be achieved e.g. by use of an alloy showing shape memory behavior.Another important aspect for future manufacturing processes is freedom of design. Individualized components can be excellently produced by additive manufacturing. By use of locally optimized parameters during layer-wise manufacturing high performance graded structures can be obtained.The research project applied for aims in the establishment of functionally graded structures that combine all aforementioned aspects in a perfect way, i.e. that are characterized by geometrical, microstructural and functional gradation simultaneously. In consequence, materials showing unprecedented properties will be producible. The material of choice, high-manganese iron based alloy, allows for activation of different deformation mechanisms. In addition to slip transformation- and twinning-induced plasticity (TRIP/TWIP) as well as superelasticity can be present in these systems. Based on a composition showing shape memory characteristics, alloys showing TRIP/TWIP will be developed. These alloys will be microstructurally graded in such way, that e.g. crack advance under cyclic loading can be stopped. Superelasticity in the shape memory alloy will allow for manufacturing parts with high internal damping characteristics. Additionally, geometric gradation will allow for a perfect synthesis of all effects in a single part.In order to be able to achieve the visionary aim of the current project, the structures have to be necessarily produced by additive manufacturing. Electron beam melting (EBM) will be employed since only this technique will avoid changes of the chemical composition of the materials.A thorough experimental approach, employing mechanical characterization under monotonic and cyclic load accompanied by intense microstructure analyses, in part in an in-situ fashion, will allow for solid conclusions regarding the high potential of the above mentioned processes to be used for manufacturing of functionally graded components made from iron-manganese based alloys.