Mikrobiegeversuche am PicoIndenter 85

Translated title of the contribution: Microbending tests with a PicoIndenter 85

Michael Reisinger

Research output: ThesisDiploma Thesis

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Abstract

Ultrafine- grained (ufg) metals, produced by severe plastic deformation methods, are polycrystalline materials, with an average grain size in the range of 100nm – 1µm. Their specific microstructure leads to special mechanical properties, such as enhanced strength combined with moderate ductility. For industrial applications dynamic load and fatigue properties are a very important material parameter. The microstructure of ufg metal is metastable, due to an increased defect density from manufacturing. Cyclic loading can therefore lead to microstructural changes, which can deteriorate the fatigue strength. In this thesis cyclic in situ bending measurements were performed on ufg Cu using a PicoIndenter PI85 from Hysitron. This device has a force resolution of 3nN, which enables cyclic softening to be seen in the stress-strain curve, caused by small microstructural changes. The ufg Cu was processed via High Pressure Torsion. As a first task, an existing testing method was successfully adjusted for this PicoIndenter leading to a stable testing process. Nanoscaled bending beams with different dimensions were produced and cyclically loaded. These cyclical fatigue tests were combined with observations of the specimen microstructure. Therefore the microstructure of the beams was characterized prior to testing and after a certain numbers of cycles. Various methods of Scanning Electron Microscopy were used for microstructural characterisation include Electron Backscatter Diffraction and backscattered electron imaging. These tests show that the microstructure of ufg Cu can coarsen during cyclic loading, due to the movement of the grain boundaries.
Translated title of the contributionMicrobending tests with a PicoIndenter 85
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Pippan, Reinhard, Supervisor (internal)
Award date19 Dec 2014
Publication statusPublished - 2014

Bibliographical note

embargoed until null

Keywords

  • ultrafine- grained
  • grain coarsening
  • fatigue
  • micromechanics

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