Fracture of ultrafine-grained metals produced by severe plastic deformation

Research output: ThesisDoctoral Thesis

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Abstract

In the last two decades bulk solids with grain sizes typically smaller than 1 micrometer down to several nanometers have attracted great scientific interest driven by their promising enhanced mechanical and physical properties. Among different possibilities to produce such materials the Severe Plastic Deformation (SPD) approach has possibly gained the most prominence currently reflected by the large number of publications in this field. This is mainly due to the technical simplicity of most processes and the large variety of processable materials. Besides classical mechanical material parameters, like strength or hardness after SPD processing, the fracture toughness is also of great concern, especially when structural applications are planned in future. Despite this, the fracture behavior of such materials has been widely omitted in the SPD community so far. In this thesis for the first time an extensive study into the fracture behavior of different SPD processed materials has been conducted. Main work was done on an one phase bcc and fcc metal, namely Armco iron and nickel. Additionally also a steel with a fully pearlitic microstructure was under investigation where experiments were performed as a function of pre-deformation. Special focus was given on a possible influence of the testing direction on the fracture toughness results. It will be shown that the deformation microstructure causes an intensive anisotropy in the fracture behavior from brittle to ductile fracture in the investigated bcc materials, Armco iron and the pearlitic steel. The anisotropy was related to one testing direction of fairly low fracture toughness which simultaneously favored a strong enhancement in the other directions. In contrast to this the fcc-example, Nickel, exhibited a good combination of strength and fracture toughness. The high fracture toughness and the less pronounced anisotropy are a result of the occurring ductile fracture compared to the brittle intercrystalline fracture of iron.
Translated title of the contributionBruch von ultrafeinkörnigen Metallen hergestellt durch Hochverformung
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Clemens, Helmut, Assessor B (internal)
  • Pippan, Reinhard, Assessor A (internal)
Publication statusPublished - 2010

Bibliographical note

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Keywords

  • Severe Plastic Deformation High Pressure Torsion fracture toughness ultrafine-grained metals anisotropy iron nickel pearlitic steel

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