SPDMETALS · Using Severe Plastic Deformation for the Processing of Bulk Nanostructured Metals

The processing of metals through the application of severe plastic deformation (SPD) provides an opportunity for achieving exceptional grain refinement to the submicrometer or the nanometer range. This grain refinement cannot be achieved by conventional methods and it introduces both significant strength and a potential superplastic forming capability. The two most important SPD techniques are Equal-Channel Angular Pressing (ECAP) and High-Pressure Torsion (HPT). In both procedures, very high strains are imposed without introducing any significant changes in the overall dimensions of the samples. This proposal outlines a research programme based on these techniques.Although processing by ECAP and HPT has attracted considerable attention, there have been few attempts to make use of this technology for the fabrication of commercial products. There are several reasons for this omission. First, both techniques produce materials having high strength but limited ductility. Second, ECAP is a labour-intensive process that must be adapted to provide a continuous processing capability. Third, the flow processes are not understood and recent experiments using HPT show remarkable similarities to fluid flow and plasma turbulence. We will take advantage of the ERC Advanced Grant to investigate these areas with three overall objectives. First, to provide an understanding of the flow processes and the microstructural evolution occurring in metals when using these techniques. Second, to develop procedures for the successful utilisation of these techniques in manufacturing. Third, to evaluate the potential for producing super-strong solids by combining HPT with a surface mechanical attrition treatment to introduce a hard surface layer of nanostructured grains.