Florian Spieckermann

Plasticity and X-ray Line Profile Analysis of the semicrystalline polymer poly(3-hydroxybutyrate)

The evolution of the microstructure during compressive deformation of the biodegradable polymer poly(3-hydroxybutyrate) (P3HB) was investigated in-situ via X-ray diffraction using synchrotron radiation. Flow curves were measured in-situ together with X-ray profiles for several degrees of deformation. The profiles were analysed using Multi-Reflection X-ray Line Profile Analysis (MXPA) adapted by the authors for semicrystalline polymers providing lamella thickness, crystallinity, and the presence and density of dislocations as a function of the deformation. In contrast to previous investigations in α crystallised isotactic polypropylene (α-iPP), P3HB does not exhibit a deformation induced increase of the dislocation density which suggests mechanisms other than dislocations to be involved in plastic deformation of P3HB.

Hysteresis and Loss Measurements on the Plastically Deformed Fe–(3 wt%)Si Under Sinusoidal and Triangular External Field

The effect of different degrees of plastic deformation on the frequency dependence of coercive field and losses in NO Fe-(3 wt%)Si was investigated measuring hysteresis loops on a ring-shaped core over a frequency range of 0.5-1000 Hz. The investigation was performed under sinusoidal and triangular external field H(t). Although H(t) induce a similar quasi-sinusoidal magnetic induction (similar hysteresis loops), the loop area is smaller for that measured by triangular applied field resulting in smaller magnetic losses. The coercive field and the total losses of all samples increase with increasing frequency; however, the influence of frequency becomes gradually smaller with plastic deformation. The total losses that increase due to plastic deformation at low frequencies become at high frequencies smaller in deformed samples than in an undeformed material. A similar behavior was found in the frequency dependence of the coercivity. Due to a periodic quasi-sinusoidal B(t), the losses were analyzed using the concept of loss separation. While the quasi-static (hysteresis) loss increases, classical and excess losses decrease with increasing deformation.

Dual self-organised shear banding behaviours and enhanced ductility in phase separating Zr-based bulk metallic glasses

Abstract The multiplication and interaction of self-organised shear bands often transform to a stick-slip behaviour of a major shear band along the primary shear plane, and ultimately the major shear band becomes runaway and terminates the plasticity of bulk metallic glasses (BMGs). Here, we examined the deformation behaviours of the nanoscale phase-separating Zr65–xCu25Al10Fex (x = 5 and 7.5 at.%) BMGs. The formation of multi-step phase separation, being mainly governed by nucleation and growth, results in the microstructural inhomogeneity on a wide range of length-scales and leads to obviously macroscopic and repeatable ductility. The good deformability can be attributed to two mechanisms for stabilizing shear banding process, i.e. the mutual interaction of multiple shear bands away from the major shear band and the delaying slip-to-failure of dense fine shear bands around the major shear band, both of which show a self-organised criticality yet with different power-law exponents. The two mechanisms could come into effect in the intermediate (stable) and later plastic deformation regime, respectively. Our findings provide a possibility to enhance the shear banding stability over the whole plastic deformation through a proper design of microstructure heterogeneities.

In Situ X-Ray Synchrotron Profile Analysis During High Pressure Torsion of Ti

X-Ray Line Profile Analysis is a powerful method to characterize the microstructure of deformed materials, especially when high energy and brilliant Synchrotron radiation enables investigations with high time and spatial resolution. Parameters like dislocation density, dislocation arrangement as well as scattering domain size and it’s distribution are parameters of a physical model of peak broadening, which can be applied to high quality diffraction measurements. A small high-pressure-torsion-machine was designed in order to perform in situ diffraction experiments during the deformation process at hydrostatic pressures up to 8 GPa in order to follow the strain as well as pressure induced microstructural characteristics of any material deformed. This was possible with the ideal design and equipment at the High-Energy-Materials-Science-beamline at PETRA III in Hamburg. Recent and First results of experiments on HPT-deformed Ti show that at 6 GPa the high pressure \( \omega \)-phase is initiated only with additional shear deformation.