Effect of microstructural and processing parameters on the fatigue properties of severely deformed iron

• Applicant: Dr.-Ing. Enrico Bruder
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 242435020

In times of constantly rising raw material and energy costs, the aspect of resource efficiency is of growing importance for both production and application of products. A possible approach to face this challenge is to improve the crucial properties of materials which are most relevant for their applications. In the field of metallic structural materials the fatigue properties are fundamental for a wide range of applications. A promising method to increase both static and cyclic strength of metal is the grain refinement by Severe Plastic Deformation (SPD) processes. However, for these processes there is only little knowledge on the implications of processing parameters (and the resulting microstructures) on the fatigue properties and especially the damage mechanisms under cyclic loading. This lack of knowledge is the impetus for the present research project which shall contribute to the basic understanding of these correlations by fundamental investigations on pure iron as a model material. The project not only focuses on ultrafine grained (UFG) microstructures but also on severely deformed states with strains in the range of 1 to 4. Such deformed states can be regarded as a precursor to UFG structures and require significantly lower manufacturing costs.The project concentrates on the Identification of the dominant damage mechanisms above 10^4 cycles and their correlation with certain features of the severely deformed microstructure and premature damage caused by the SPD processing. For this purpose processing and microstructural parameters will be systematically varied to investigate their effect on the dominating damage mechanism as well as on the cyclic strength. Through the variation of the prestrain in the range of 1 to 4, the potential of precursors states as a cost-efficient alternative to UFG materials will be evaluated. Furthermore, UFG microstructures with a prestrain above 6 will be generated with varying aspect ratio and varying damage relevant processing parameters such as strain rate and hydrostatic stress. These will be used to investigate the impact of the effective glide length in elongated structures and relevance of premature damage from the SPD processing on the fatigue properties and their anisotropy.

• DFG Programme: Research Grants