Advanced Rolling Technologies for Producing Ultrafine-grain/nanostructured Alloys

Ultrafine-grained materials show high strength at ambient temperature, high-speed superplastic deformation at elevated temperatures, and high corrosion resistance. Such materials have attracted increasing attention in the past twenty years. A number of severe plastic deformation techniques, such as equal-channel angular press, high pressure torsion, groove pressing, twist extrusion, asymmetric rolling, and accumulative roll bonding have been used to develop ultrafine-grained bulk materials. The equal-channel angular press, high pressure torsion, twist extrusion and groove pressing techniques suffer from some drawbacks: firstly, forming machines with large load capacities and expensive dies are indispensable for these processes; secondly, the productivity is relatively very limited; thirdly, the techniques are only suitable for small samples. Compared with equal-channel angular press, high pressure torsion, twist extrusion and groove pressing, the accumulative roll bonding and asymmetric rolling techniques can be used to produce continuous ultrafine-grained sheets in large quantities. In this paper, a survey of relatively recent rolling technologies is presented. The merits and drawbacks of each technique are examined. These techniques are: (1) Asymmetric cryorolling, which has potential for large-scale industrial production of nanostructured materials; (2) Four-layer accumulative roll bonding, which has potential to produce nanostructured materials at room temperature with high bonding quality, used for fabrication of ultrafine material sheets; (3) Asymmetric Rolling of accumulative roll bonding-processed sheets, which has potential for large-scale industrial production of nanocomposite foils.