Adaptive Structural Materials
A major obstacle to traditional alloy design is the inverse relation between strength and ductility (right figure). As shown by the blue fields, conventional hardening mechanisms lead to a dramatic decrease in ductility. While modern advanced steels based on displacive transformations can partly break the inverse relation ship (green fields), with adaptive structural materials we aim at boosting metallic properties to yet unavailable regions by exploring new design strategies. The key idea of ASMs is based on the novel strategy of designing, synthesizing and characterizing intrinsic phase instability. As shown schematically in the ASM logo (left figure), the philosophy behind that is to either incorporate dispersed phases that are close or even beyond their mechanical and thermodynamic stability limit into otherwise stable bulk alloys or to design the bulk material itself such that it is at the verge of mechanical/thermodynamic stability. In either case the newly designed phases shall gradually transform under mechanical loading into secondary phases (i.e. martensite) or extended defects (e.g. twin bundles).
A strength but at the same time challenge of our group is the intimate coupling between quantum-mechanically guided design (first principles) and state-of-the-art experimentation. To address this challenge we can draw on high-quality work we have conducted previously. On the theory front, we have developed and applied a multitude of approaches over the recent years to efficiently and accurately tackle the finite temperature description from first principles (see "Projects" link below). With this, we resolve a serious but very common drawback of typical first-principles applications. A key future challenge is the incorporation of the various methods and techniques into a single unified approach, since we expect various physical mechanisms (electronic, vibrational = quasiharmonic + anharmonic, magnetic, structural defects= vacancies + dislocations +..., configurational) to be crucial in the design of ASMs. On the experimental front, we employ (i) various high-end metallurgical production and processing routes, (ii) multi-scale microstructural characterization (down to atomic resolution) and mechanical testing, and (iii) high-resolution in-situ characterization of phase transformations and microstructural deformation mechanisms. The latter is of particular importance and a key future challenge for ASMs, since the determination of the stable regimes of the introduced unstable phases is in most cases only possible through such in-situ analysis.