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The microstructure of metals and alloys has a significant impact on material properties.
Therefore a detailed investigation of this characteristic is mandatory for the understanding of the behavior of the material of interest.
Beside of the mechanical behavior the impact of the microstructure on thermal and electrical properties is of importance. At cryogenic temperatures thermal processes are hindered and the thermal coupling from inside the material to the cooling fluid depends significantly on the thermal conductivity and heat capacity.
In this work pure copper (OFHC) is used as a reference fcc system with intrinsic stacking fault energy γSFE lower 60 mJm-2 [1], where the grain size can be systematically adjusted by different deformation processes. By severe plastic deformation (SPD), in peculiar the so-called equal channel angular pressing (ECAP) reduce the grain size down to nanometer scale by several consecutive deformation passes.
The distinctive microstructure is characterized by electron backscatter diffraction as well as scanning electron microscopy. Depending on the deformation path, different amounts of twinning, orientation and grain size are observed. Measurements of thermal conductivity and heat capacity are performed. The results are related to the gradually changed grain sizes and examined how far a correlation to mechanical properties is possible.
[1]: J. Freudenberger, A. Kauffmann, H. Klauß, T. Marr, K. Nenkov, V. S. Sarma,, L. Schultz. Studies on recrystallization of single-phase copper alloys by resistance measurements 2010. Acta Materialia , 58, 2324-2329.