Anisotropic static and cyclic mechanical properties in nanolayered pearlitic steelsWednesday (26.09.2018) 14:30 - 14:45 S1/01 - A03 Part of:
Severely deforming a fully pearlitic steel by high pressure torsion produces a high strength composite consisting of alternating ferrite and cementite lamellae with 20 nm and 3 nm spacing, respectively. This refinement results in a strength increase of almost three times compared to the as-received state, however, a distinct dependency on the loading direction with respect to the lamellae orientation exists. Maximum strength levels of 3.5 GPa are only achieved when the load is imposed perpendicular or parallel to the lamellae, whereas the strength for inclined loading conditions is only 2.8 GPa. Micro compression experiments performed in-situ inside a scanning electron microscope revealed that the origin of this difference lies in the tendency of nanocomposites to localize strain in shear and kink bands. It has been found that the characteristics of the strain localization vary with the loading direction of the lamellae and affect the materials strain hardening capacity. It will be shown, that a change in the deformation mode from compression to bending enables the suppression of large scale shear bands. Thereby the plastic deformability can be enhanced significantly, making these high strength materials promising aspirants for fatigue loading conditions. Their cyclic behavior was studied by in-situ micro bending experiments under low cycle fatigue conditions. Two different loading directions were studied, with the lamellae being aligned perpendicular and parallel to the load, in order to account for an orientation dependent behavior. Although strain localizations were not observed an anisotropy was revealed in terms of the nanocomposite’s lifetime. It will be shown that not only crack propagation itself, but also the plastic strain to initiate a crack from the surface can be governed by the lamellar alignment.