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

高压扭转法制备纳米结构材料原理的评价技术：通过严重塑性变形(SPD)对金属进行加工正引起材料科学界的关注。这种类型的加工包括通过施加强烈应变将大量位错引入样品中，但不会引起工件横截面尺寸的任何变化。SPD工艺的主要优点是，它可以在不引入残余气孔率或污染的情况下显著细化晶粒。SPD加工的超细晶材料在常温下表现出极高的强度和改善的韧性，以及在高温下实现快速超塑性成形的潜力。这笔赠款涉及使用高压扭转(HPT)的SPD处理，其中材料在同时扭转应变下受到非常高的压力。世界各地的初步结果表明，与其他SPD技术相比，HPT工艺具有优势，因为它导致了更小的颗粒尺寸，通常在纳米范围内。本研究项目涉及HPT加工的基本领域：(1)在材料内部形成均质化所涉及的因素；(2)表观饱和晶粒度的重要性；(3)克服高强度伴随低延展性的问题的程序的制定；以及(4)通过将HPT与其他加工技术相结合来实现改善机械性能的可能性。非技术性：该项目培训一名研究生和一名博士后研究方法，并通过国内和国际合作提供与其他研究人员互动的机会。这些合作包括许多来访者来南加州大学几天或长期约会。还特别尝试将代表性不足群体的成员纳入该方案。本科生通过在高级项目实验室内为机械工程毕业生提供为期一学期的项目来参与开发。当地高中生和他们的老师通过定期的海报展示和特殊活动，如每年一度的南加州大学开放日，让学生和他们的老师接触到研究活动，在此期间，校园对当地社区成员开放。

An Evaluation of the Principles of High-Pressure Torsion for Producing Nanostructured MaterialsTECHNICAL: 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.