Projekt

The objectives of this research project are to study the fatigue mechanisms occurring in selected ultrafine-grained (UFG) metallic materials, to elucidate the microstructural fatigue mechanisms and to derive means to optimize the fatigue resistance. The so-called UFG-materials represent a “new” class of materials with grain sizes of ca. 100 – 300 nm which are produced by severe plastic deformation in the form of repeated massive shear deformations in the ECAP-process (ECAP: equal channel angular pressing). UFG-materials possess an exceptionally high strength and are hence considered as excellent candidates for special applications. The cyclic deformation behaviour of UFG-materials has only been studied scarcely so far. Cyclically deformed UFG-materials frequently exhibit early fatigue damage related to strong cyclic softening caused by macroscopic shear banding and dynamic grain coarsening of the heavily deformed metastable microstructure (even at rather low homologous temperatures of ca. 0.2 Tm, Tm: melting temperature).
In this project, criteria based on the experimental results obtained are to be derived with the goal to improve the cyclic deformation and fatigue resistance of selected UFG-materials. For this purpose, studies will be performed on UFG-copper as a model material and on UFG specimens of the Al-alloy AA 6061 and of α-brass at temperatures between –50°C and ca. +200°C, both in strain and in stress control. Additional experiments are planned on an austenitic stainless steel. Based on the accompanying microstructural studies, a fatigue life model will be formulated.