Comparative study on the miscibility of Cu-Fe-Co compounds processed by methods of severe deformation

This thesis deals with investigations regarding the microstructural development of severe plastically deformed samples by high-pressure torsion of the ternary system Cu-Fe-Co, whereby the individual components (besides Co-Fe) are immiscible at the thermodynamic equilibrium. Two various compositions, Cu20(Fe70Co30)80 and Cu20(Fe15Co85)80, were fabricated out of elemental powders, then deformed by high-pressure torsion and exposed to subsequent conventional annealing treatments. The obtained microstructures were compared by using light microscopy, scanning electron microscopy, X-Ray diffraction and Vickers hardness measurements. A single-phase microstructure could be reached for Cu20(Fe15Co85)80. In contrast to that, the Fe-rich samples exhibit residual particles embedded in a supersaturated matrix. The resulting microstructure consists therefore of two phases. An enhancement of intermixing was achieved with powder mixtures, which were pre-treated by ball milling and subsequently deformed by high-pressure torsion. Ball milling, however, led to brittle samples which exhibit more cracks. Nevertheless, grain sizes in the nanocrystalline regime were obtained for all asdeformed samples. Furthermore, conventional annealing led to a homogenous microstructure and grain coarsening in each case. In comparison, the as-deformed and annealed Cu20(Fe15Co85)80 samples exhibit a higher thermal stability