SUMMARYPitcher plants of the genus Nepenthes efficiently trap and retain insect prey in highly specialized leaves. Besides a slippery peristome which inhibits adhesion of insects they employ epicuticular wax crystals on the inner walls of the conductive zone of the pitchers to hamper insect attachment by adhesive devices. It has been proposed that the detachment of individual crystals and the resulting contamination of adhesive organs is responsible for capturing insects. However, our results provide evidence in favour of a different mechanism, mainly based on the stability and the roughness of the waxy surface. First, we were unable to detect a large quantity of crystal fragments on the pads of insects detached from mature pitcher surfaces of Nepenthes alata. Second, investigation of the pitcher surface by focused ion beam treatment showed that the wax crystals form a compact 3D structure. Third, atomic force microscopy of the platelet-shaped crystals revealed that the crystals are mechanically stable, rendering crystal detachment by insect pads unlikely. Fourth, the surface profile parameters of the wax layer showed striking similarities to those of polishing paper with low grain size. By measuring friction forces of insects on this artificial surface we demonstrate that microscopic roughness alone is sufficient to minimize insect attachment. A theoretical model shows that surface roughness within a certain length scale will prevent adhesion by being too rough for adhesive pads but not rough enough for claws. Supplementary material available online at

In the production of high‐manganese TRIP and TWIP steels, significant micro‐segregation effects are observed after solidification. Homogenization can be achieved by heat treatment followed by deformation at a significant time and effort (forging, annealing, hot rolling). In an attempt to achieve the best homogeneous microstructure and reduced thermomechanical processing, the cast alloy is treated by electroslag remelting (ESR). After a simple hot rolling procedure with a thickness reduction of 90% and without further heat treatment, micro‐segregation of manganese can be reduced to about 5 wt%. There is a potential to achieve even lower values with further optimization of the ESR process and an adapted thermomechanical processing.

The mechanical properties of high manganese steels are linked to their hardening mechanisms and their intrinsic behavior during deformation. The characterization of mechanical properties is influenced by the localization of plastic flow and the effect of this localization on the material. Depending on grain size, temperature, and extrinsic strain rate localization of strain, adiabatic heating, and hardening vary in spatial and temporal extent. Even at small strain rates the adiabatic heating of samples reaches temperatures more than 100 K over initial testing temperature due to the sharp localization and last but not least this heating is also dependent on the tested sample size. Furthermore, temperature influences the activated mechanisms of plastic flow. The characterization of temperature increase, strain distribution, and local hardening is pursued in tensile tests with application of infrared thermography. With those techniques it is possible to gather correlations between local strain and temperature. The analysis of dynamic strain ageing effects is also carried out by evaluation of the instantaneous strain rate, the strain rate in the gauge length, in dependence of stress in different alloys, as well as at different strain rate regimes. Thus it is possible to distinguish the onset of TRIP, TWIP and DSA.

Steels show different types of deformation mechanisms. Those mechanisms inherit different geometrical influences on the shape of grains on the materials surface and lead to changes in surface topography during deformation. Within the Collaborative Research Center SFB 761 – Steel Ab Initio a way of strain dependent microstructure characterization concerning deformation mechanisms of austenitic high manganese steels is evaluated. With the measurement of a polished surface with confocal microscopy it is possible to observe not only the macroscopic visible orange peel, but also the effects that occur on grain size level during deformation. In a practical approach in‐situ measurements of surface topography are performed in incremental strain steps during tensile test. Each measurement delivers the evolution of surface roughness as well as information on the surface topography of single grains in a representative measurement area. The results of in situ confocal microscopy of 3 different steel concepts are presented and evaluated regarding the relevance of the technique for the deformation characterization.

KurzfassungNeue Stähle weichen in ihrer Zusammensetzung, ihren Gefügen und ihren Eigenschaften zum Teil erheblich von den seit Jahrzehnten bekannten Werkstoffen ab. Die Verwendung höherer Legierungsgehalte und mehrstufiger Glühungen führt zu neuen Problemen in der Charakterisierung dieser Güten. Die klassischen Verfahren der Metallografie und Werkstoffprüfung sind zumeist auf einphasige Werkstoffe ausgelegt und liefern dort gute Ergebnisse. Werden jedoch Werkstoffe mit erhöhtem Legierungsgehalt und/oder speziellen Gefügen betrachtet, ergibt sich die Notwendigkeit für die erweiterte Charakterisierung mit neuen Methoden. Im vorliegenden Beitrag werden einige Ansätze zur Beschreibung neuer Stähle vorgestellt.