Stability of the microstructure of superfine-grained, non-alloy steels under cyclic loading

Superfine-grained structures with submicron grain size can be realized in pure metals by severe plastic deformation (SPD) under quasi-hydrostatic state of stress. These states have higher static strengths compared to states with conventional grain sizes. Within the research project, ultra-fine grained (UFG) ferritic pearlitic steels will be analyzed and optimized in regard to their fatigue properties. The process of high pressure torsion (HPT) will be used for generating an ultra-fine grained structure by putting the specimen (im Ausgangszustand) between two punches that are rotating against each other under high quasi-hydrostatic pressure (Fig.1). The massive, plastic deformation results in a homogeneous, superfine-grained microstructure, that is shown in figure 2 for a steel with a relevant, average grain-size of 10nm [2]. The characterization of the fatigue behavior is carried out using micro test equipment (Fig.4) to realize 4-point bending tests mainly in the HCF (High cycle Fatigue) range. The aim of the project is to produce a stabile microstructure also under cyclic loading. Transmission electron microscope and electron scanning microscopy are available to characterize the microstructure after cyclic loading. The project takes place in close collaboration with the Institut für Nanotechnologie (KIT, Karlsruhe).

Literature:

[1] R.Z. Valiev, R.K. Islamgaliev, I.V.Alexandrov, Progress in Material Science 45 (2000) 103.

[2] Yu. Ivanisenko, R. Wunderlich, R.Z. Valiev, H.-J. Fecht, Scripta Materialia 49 (2003) 947

Contact: Prof. Dr.-Ing. Eberhard Kerscher