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Pure nickel was deformed by a combination of conventional and cyclic high-pressure torsion. The change of the mechanical strength during the deformation was measured, and microstructural features were determined for specific cases. A cyclic deformation of the ultrafine-grained structure obtained by severe plastic deformation leads to a localization of the deformation due to deformation-induced grain coarsening. Furthermore, an explanation for the observed decrease of the mechanical strength after reversal of the strain path is given.

The fully pearlitic rail steel R260 was deformed by equal channel angular pressing at room temperature. Changes in the microstructure as well as changes in mechanical properties were determined. With increasing predeformation significant changes of the tensile strength, the fatigue crack propagation rate and the fracture toughness occurred. Due to the alignment of the cementite lamellae, also a markedly anisotropy in all these properties evolved.

Cyclic high-pressure torsion, a modified version of high-pressure torsion, is applied to Armco iron and nickel. The results in terms of microstructure and flow stress are compared to samples deformed by conventional high-pressure torsion. For both processes and both materials, a saturation in the decrease of the structure size and the increase in the flow stress is observed. The minimum size of the structural elements which is obtainable is smallest for the conventionally high-pressure torsion deformed samples and increases with decreasing strain per cycle in cyclic high-pressure torsion.

The effect of the different processing parameters on the refinement during severe plastic deformation is evaluated. The attention is focused to very high strains, where saturation in the structural refinement is observed. The single phase metals and alloys show a relatively uniform behaviour, with increasing strain the size of structural elements decreases and reaches saturation between equivalent strains of 5 to 50. The resulting ultra fine or nanostructured granular microstructure contains mainly high angle grain boundaries. Alloying, the temperature, and the strain path are the most important parameters controlling the saturation in the structural refinement. The behavior of the dual and multiphase materials during SPD is more complex, it varies from simple homogenisation of the phase distribution, fragmentation of one phase to disintegration and supersaturation of the phases. Severe plastic deformation of these types of materials offers the potential for the production of new types of materials with a nanocrystalline or a nanocomposite structure for a broad range of industrial applications.

YBa2Cu3O7 is a high-temperature superconductor. Due to its complex lattice structure, belonging to the layered perovskite family, a strong biaxial texture of the grains is necessary to achieve technically relevant currents. In this paper, coarse-grained Ni, Ni-4at.% W, and electrolytic copper (E-Cu) obtained from swaged rods, and ultra-fine grained E-Cu produced by equal channel angular pressing, were thermo-mechanically processed. The development of the primary recrystallisation of the cube texture was studied and compared to determine the suitability of these materials as lattice-matched templates for coated conductor applications. Electron backscatter diffraction was performed to measure the texture and microstructure at various deformation levels and annealing temperatures. The texture sharpness formed in E-Cu with a coarse-grained starting microstructure proved superior, and it correlates with an anomaly observed in the temperature sensitivity of the flow stress in tensile tests, arising from crystal rotations.

A fully pearlitic steel was deformed by high-pressure torsion up to very high strains, and the changes in the microstructure were determined by analytic and conventional transmission electron microscopy. The imposed strain leads to a fragmentation and an alignment of the cementite lamellae parallel to the shear plane. The electron energy-loss near-edge-fine structures of the Fe-L2,3-edge of the iron matrix and the cementite lamellae were measured with high spatial resolution. The results indicated that after high-pressure torsion, the iron matrix contains finely dispersed carbon-rich areas that do not show the electronic fingerprint of cementite. However, the refinement in microstructure leads to an enormous increase in mechanical strength.

To study the influence of shear deformation on the evolution of the microstructure and the mechanical strength in rail steels, three steels with different microstructure (two pearlitic, one bainitic) were deformed by High Pressure Torsion (HPT). In order to evaluate in addition the effect of the strain path, a cyclic form of HPT was applied. The mechanical strength was determined by means of in-situ measurement of the flow stress and microhardness measurements. The differences of the mechanical strengths between the monotonic and cyclic deformed samples clearly indicate that a monotonic deformation promotes higher dislocation densities and leads to the assumption that dissolution of the cementite takes place more pronounced.

Severe plastic deformation (SPD) has been applied to two classes of metallic materials, single phase and dual phase materials. The applied shear strain has been varied between 1 and 1000 and the homologous temperature between 0.08 and 0.4. The deformation experiments are performed by high pressure torsion (HPT). The resulting microstructures were investigated by backscattered electron imaging, orientation image microscopy, and in selected cases by transmission electron microscopy. It will be shown that the behavior of single phase material is relatively uniform. With increasing strain, the size of the structural elements decreases and reaches a saturation between a shear strain of 10 to 100. The temperature and the alloying are the main parameters, which controls the saturation size of the structural elements (grains). The behavior in the dual phase materials is more complex, it varies from simple homogenisation, fragmentation of one phase, to desintegration and supersaturation of the phases.

Severe plastic deformation has been applied to Armco iron and copper by means of high pressure torsion. The evolution of the shear stress during deformation was measured under different hydrostatic pressures. By applying a simple model for a strain hardening, the shear stress–shear strain curves are fitted and the influence of the hydrostatic pressure is studied. These results are compared to microhardness measurements, tensile strength and the microstructural evolution.

Pure copper is deformed by high pressure torsion and the resulting microstructure is studied. Small structural elements are formed. Their size decreases with increasing strain and reach a steady-state. The misorientation between neighbouring structural elements increases with strain and finally reaches a nearly random distribution. The steady-state size decreases with increasing pressure and decreasing temperature. The shape of the elements suggests the continuous formation of new elements during steady-state deformation. This would be a process similar to dynamic recrystallisation.

The rail steel S900A and Armco-iron have been deformed by severe plastic deformation, the microstructural evolution and the changes in microhardness have been investigated. In both materials the deformation leads to a decrease in structure size. In the case of the steel an alignment of the lamellae parallel to the shear plane and a decrease of the lamellae spacing is observed. Lamellae which have been originally not favourably aligned are heavily bent and broken into small fragments. This refinement is also reflected in the evolution of the microhardness.

On the surface of rails a severely deformed layer is formed during the application due to the permanent loading of a rail-wheel contact [1]. In this deformed layer cracks are formed and may grow to a critical length. Therefore, it is of great importance to determine the fracture properties of these plastically deformed regions to enhance finite element calculations for live time predictions and define service intervals.

A filamentary composite elaborated by cold drawing was processed by High Pressure Torsion (HPT). The nanostructure resulting from this severe plastic deformation (SPD) was investigated thanks to scanning electron microscopy, transmission electron microscopy, X-ray diffraction and 3D atom probe. Although the mutual solubility of Cu and Fe is extremely low at room temperature in equilibrium conditions, it is shown that nanoscaled Fe clusters dissolve in the Cu matrix. The non-equilibrium copper supersaturated solid solutions contain up to 20at.% Fe. The driving force of the dissolution is attributed to capillary pressures and mechanisms which could enhanced the atomic mobility during HPT are discussed. We conclude that the interdiffusion is the result of a dramatic increase of the vacancy concentration during SPD., 20 pages

This is a copy of the slides presented at the meeting but not formally written up for the volume. Grain size reduction induced by severe plastic deformation (SPD) and the resulting mechanical properties have been widely investigated for pure metals but less is known and reported about multi-phase materials. To study the grain size reduction mechanisms in multiphase structure subjected to SPD, two copper based composites (Cu-10%Fe and Cu-43%Cr) were severely deformed by torsion under high pressure. The grain size achieved with these composite materials is much smaller than in pure metals. It is for example in a range of 10 to 20 nm for the Cu-43%Cr composite, e.g. one order of magnitude lower than in pure Cu processed by SPD. Three dimensional atom probe data show also the formation of non equilibrium supersaturated solid solutions. The mechanisms of the deformation induced intermixing are discussed together with its influence on the mechanical properties.