Nanomechanical investigations of plasticity in topologically close-packed phases at high temperatures

• Applicant: Professorin Sandra Korte-Kerzel, Ph.D.
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2013 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 246436525

The scientific aim of this project is the comprehensive characterisation of plasticity in the intermetallic, topologically close packed precipitates (TCP phases) which form, for example, in the highly alloyed superalloys. They affect rafting during creep and are associated with a reduction in lifetime by the initiation of cracks and the softening of the matrix by extraction of important alloying elements.In the first phase of this project, the mechanical properties, deformation mechanisms and defect structure of the µ-phase Fe7Mo6 have been investigated using micromechanical test methods in combination with scanning and (high resolution) transmission electron microscopy. First investigations of the σ-phase revealed a stoichiometry dependence of its deformation. Within the scope of this work, a computer-assisted analysis for unknown glide planes in complex crystals has been developed and implemented which has accelerated and expanded the identification of slip traces formed around indentation. In addition, the nanoindentation methods was expanded to now reach the operating temperature of superalloys at 1000 °C.Based on these results, a complete determination of the deformation mechanisms, their thermal activation and dependence on stoichiometry is planned for the µ, σ und Laves TCP phases in the technically relevant Fe-Mo system. To this end, micromechanical test methods, such as nanoindentation, high temperature nanoindentation, nanoindentation-strain rate jump testing and micropillar compression will be used and combined with subsequent analysis to the atomic scale. Here, the focus will be laid on the comparison of the deformation mechanisms and dislocation structures in the pure Laves phase and the Laves phase layers within the µ-phase. The existing results have shown that at room temperature deformation of the µ-phase occurs by synchroshear on the Laves triple layers. Consideration of deformation of complex crystals based not on a complete unit cell, but rather its constituent sub-cells, would make the categorisation and identification of suitable complex intermetallic phases for defined applications much easier. We therefore expect that the planned investigations will affect the evaluation of future applicability of complex intermetallic phases and the effects of alloying elements, for example in high temperature applications or as reinforcement phases in high strength materials.

• DFG Programme: Research Grants