No abstract

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.

No abstract

KeywordsSevere plastic deformation, nanocrystalline microstructure, atom-probe field ion microscopy, vacancies, bulk diffusion. AbstractA 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.

No abstract

Afully pearlitic steel was deformed by high-pressure torsionuptovery high strains, and the changes in the microstructure were determined by analytic and conventional transmission electron microscopy.The imposedstrain leads to afragmentation and an alignment of the cementite lamellae parallel to the shear plane. The electron energy-loss near-edge-fine structureso ft he Fe-L 2,3 -edge of the iron matrix and the cementite lamellae were measured with high spatial resolution. The results indicated that after high-pressuretorsion, the iron matrixcontains finely dispersed carbon-rich areas that do not showt he electronic fingerprint of cementite. However,t he refinement in microstructure leads to an enormous increase in mechanical strength.

No abstract

No abstract