The processing of metals through the application of severe plastic deformation provides an opportunity for achieving exceptional grain refinement. In high-pressure torsion (HPT), where a disk is subjected to a pressure and concurrent torsional straining, it is often feasible to reduce the grain size of a metallic alloy to the nanometer range (<100 nm). These ultrafine-grained materials exhibit very high strength and a potential for use in superplastic forming processes. Experiments will be conducted to address four major issues in HPT processing. First, experimental parameters that are needed to achieve a fully homogeneous microstructure using HPT will be evaluated. Second, both experimental and theoretical factors that determine the equilibrium grain sizes achieved in HPT will be investigated. Third, the origin of unusual flow patterns, including the presence of swirls and vortices, that have been reported in materials processed by HPT will be investigated. Fourth, HPT will be combined with a surface mechanical attrition treatment (SMAT) to evaluate the opportunity for producing hardened disks that will have considerable use in industrial applications.
NON-TECHNICAL SUMMARY
The grain size of a polycrystalline metal is a critical parameter because it determines fundamental properties such as strength and flow characteristics. The processing of metals by high-pressure torsion (HPT) is a relatively new procedure that provides an opportunity for producing bulk metals with extremely small grain sizes. These metals have a very high strength and also exhibit other attractive properties such as excellent formability and good wear resistance. The proposed research is designed to investigate some of the fundamental properties of the HPT processing technique with the objective of optimizing the technique so that it can be used to produce materials of interest for industrial applications. The research group will contain one post-doctoral fellow and at least one student, and they will have an opportunity to participate in a major and important research activity. We will also collaborate with several international groups in Japan, Brazil and Europe, and this will provide the students with an international experience.
