An Evaluation of the Principles of High-Pressure Torsion for Producing Nanostructured Materials

University Of Southern California, Los Angeles CA

Investigators

Abstract

An Evaluation of the Principles of High-Pressure Torsion for Producing Nanostructured Materials TECHNICAL: The processing of metals by severe plastic deformation (SPD) is attracting attention within the materials science community. This type of processing involves introducing a large number of dislocations into the sample by imposing intense strain but without incurring any change in the cross-sectional dimensions of the work-piece. The primary advantage of SPD processing is that it can lead to significant grain refinement without the introduction of residual porosity or contamination. The ultrafine-grained materials processed by SPD exhibit exceptionally high strength and improved toughness at ambient temperatures together with the potential for achieving rapid superplastic forming capabilities at elevated temperatures. This grant is concerned with SPD processing using high-pressure torsion (HPT) where materials are subjected to very high pressures under concurrent torsional straining. Preliminary results around the world demonstrate that HPT processing offers advantages over other SPD techniques because it leads to a smaller grain size often within the nanometer range. This research program addresses fundamental areas of HPT processing: (1) the factors involved in developing homogenization within the material; (2) the significance of apparent saturation grain sizes; (3) the formulation of procedures for overcoming the problem of higher strength accompanied by lower ductility; and (4) the potential for achieving improved mechanical properties by combining HPT with other processing techniques. NON-TECHNICAL: The program trains one graduate student and one post-doc in research methodology and provides opportunities for interactions with other researchers through national and international collaborations. These collaborations involve numerous visitors coming to USC either for a few days or for long-term appointments. Special attempts are made to incorporate members of under-represented groups into the program. Undergraduate students are involved through the development of semester-long projects offered within the Senior Projects Laboratory for students graduating in Mechanical Engineering. Local high school students and their teachers are exposed to the research activities through regular poster presentations and special activities such as the annual USC Open Day during which the campus is open to members of the local community.