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

技术：金属的严重塑性变形（SPD）加工正在引起材料科学界的关注。这种类型的加工涉及通过施加强烈的应变在样品中引入大量的位错，但不会引起工件横截面尺寸的任何变化。SPD加工的主要优点是，它可以导致显著的晶粒细化，而不会引入残余孔隙或污染。SPD加工的超细晶材料在室温下表现出极高的强度和韧性，并具有在高温下实现快速超塑性成形的潜力。该资助涉及使用高压扭转（HPT）处理SPD，其中材料在并发扭转应变下承受非常高的压力。世界范围内的初步结果表明，HPT加工比其他SPD技术具有优势，因为它通常在纳米范围内导致更小的晶粒尺寸。本研究项目涉及HPT加工的基本领域：(1)材料内均质化的因素；(2)表观饱和粒度的显著性；(3)制定克服高强度低延性问题的程序；(4)通过将HPT与其他加工技术相结合来改善机械性能的潜力。非技术：该项目培养一名研究生和一名博士后的研究方法，并通过国内和国际合作提供与其他研究人员互动的机会。这些合作涉及许多访客来南加州大学，有的是几天，有的是长期预约。特别尝试将代表性不足的群体成员纳入该计划。本科学生通过高级项目实验室为机械工程专业毕业的学生提供的学期项目的开发。当地的高中学生和他们的老师通过定期的海报展示和特殊活动，如每年的南加州大学开放日，校园向当地社区成员开放，从而接触到研究活动。

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.