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The Mechanical Properties in the Vicinity of Grain Boundaries in Ultrafine-Grained and Polycrystalline Materials Studied by Nanoindentations

Published online by Cambridge University Press:  15 March 2011

E. Schweitzer ,
K. Durst ,
D. Amberger  and
M. Göken
E. Schweitzer
Affiliation:
Department of Materials Science & Engineering, University Erlangen-Nuremberg 91058 Erlangen, Martensstrasse 5, Germany
K. Durst
Affiliation:
Department of Materials Science & Engineering, University Erlangen-Nuremberg 91058 Erlangen, Martensstrasse 5, Germany
D. Amberger
Affiliation:
Department of Materials Science & Engineering, University Erlangen-Nuremberg 91058 Erlangen, Martensstrasse 5, Germany
M. Göken
Affiliation:
Department of Materials Science & Engineering, University Erlangen-Nuremberg 91058 Erlangen, Martensstrasse 5, Germany
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Abstract

The strength of structural materials strongly depends on the structure and properties of grain boundaries. Interfaces usually act as barriers to dislocation motion and therefore strengthen materials with decreasing grain size, quantitatively described by the well-known Hall-Petch relation. However, interfaces in nanocrystalline materials are often covered with impurities or second phases, which may influence the mechanical properties. With nanoindentation testing it is now possible to probe the strength of interfaces like grain boundaries directly on a nanometer scale. Therefore this method was used to investigate the properties in the vicinity of grain boundaries in polycrystalline materials with conventional grain size and in ultrafine-grained metals prepared by equal channel angular pressing (ECAP), where no impurities are introduced during processing. Measurements on an austenitic steel clearly show a decreasing hardness close to the interface opposite to the general expected behavior of strengthening. In this case segregation effects strongly influence the mechanical properties near the boundaries. The nanoindentation investigations on ultrafine-grained Al and Cu show a strong strain rate sensitivity. Inelastic effects are also found between unloading-loading segments during indentations.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 819: Symposia N/P – Interfacial Engineering for Optimized Properties III , 2004 , N4.9/P4.9
Copyright
Copyright © Materials Research Society 2004

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