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

目前的合金和工艺必须满足具有挑战性的要求。从资源效率的角度来看，轻量化设计具有极其重要的意义。为此，大量使用高比强度的材料。局部性能的调整可以进一步提高这些高性能合金的轻量化潜力。有可能以这样的方式来定制本地材料属性，从而完美地满足本地加载情况所设定的要求。这可以通过控制几何结构、微观结构和化学成分来获得。不仅可以影响强度和延展性，材料的功能化也是可能的。后者可以通过使用表现出形状记忆行为的合金来实现。未来制造工艺的另一个重要方面是设计的自由。通过加法制造可以很好地生产个性化的部件。在层次化制造过程中，利用局部优化的工艺参数可以获得高性能的梯度结构，该研究项目的目标是建立一种功能梯度结构，将上述各方面完美地结合在一起，即同时具有几何、组织和功能梯度的特征。因此，显示出前所未有的性能的材料将是可以生产的。选择的材料是高锰铁基合金，允许激活不同的变形机制。除了滑移、相变和孪生诱发塑性(TRIP/TWIP)以及超弹性外，这些体系中还可能存在超弹性。基于一种显示形状记忆特性的成分，将开发具有TRIP/TWIP的合金。这些合金将以这样的方式进行组织分级，例如，可以阻止在循环载荷下的裂纹扩展。形状记忆合金的超弹性将允许制造具有高内部阻尼特性的部件。此外，几何渐变将允许在单个部件中完美地合成所有效果。为了能够实现当前项目的愿景目标，这些结构必须通过添加制造来生产。将采用电子束熔炼(EBM)技术，因为只有这种技术才能避免材料化学成分的变化。一种彻底的实验方法，采用单调和循环载荷下的力学表征，并部分以原位方式进行密集的微观结构分析，将允许对上述工艺用于制造由铁-锰基合金制成的功能梯度部件的高潜力做出坚实的结论。

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.