The Role of Impurities in Superplastic Deformation and Cavitation

9810422穆罕默德这项研究集中在金属合金超塑性流动的亚结构细节上，特别是超塑性区域(区域II)。这包括系统地检查选定类型的杂质原子对超塑性流动和空化的影响。这种检查解决了不同杂质之间对气蚀和延展性的协同作用。深入研究了杂质类型和杂质能级对空化过程的影响，考察了空穴形核和变形与空穴生长之间的关系。表征了晶界上的杂质分布。与超塑性变形相关的微观结构细节(边界滑动和迁移、颗粒形状、颗粒旋转和韧带)被确定为杂质水平和类型、大应变(30%)和变形方式(拉伸和双剪切)的函数。对锌-22%铝、铅-62%锡和铝-33%铜三种不同的模型材料进行了研究。对于这些合金，测试了高纯级和掺杂杂质的级。此外，还选择了一些商业超塑性合金，根据为空心杆提出的新的力学模型，研究了空心杆的取向与应变率的关系。还研究了主要杂质，如铜和镁，对两种具有高应变速率超塑性的近纳米尺度铝合金的空化和塑性行为的影响。一种创新的技术使用了扁平的双剪切试件来简化测试程序，并避免了与扭转和拉伸加载相关的问题。%本项目的研究成果将对金属合金超塑性科学技术产生重大影响。它将促进对商业超塑性合金加工的理解，并可能导致这些材料性能的改善。***

9810422 Mohamed This research focuses on the substructural details of superplastic flow in metal alloys with special focus on the superplastic region (region II). This includes a systematic examination of the effects of selected types of impurity atoms on superplastic flow and cavitation. Such an examination addresses synergistic interactions among various impurities on cavitation and ductility. An in-depth study of the effects of impurity type and level on the cavitation process is carried out, looking at cavity nucleation and the relationship between deformation and cavity growth. Impurity distribution at boundaries is characterized. Microstructural details associated with superplastic deformation (boundary sliding and migration, grain shape, grain rotation, and ligaments) are determined as a function of impurity level and type, large strains (30%), and deformation mode (tension and double shear). Three different model materials, Zn-22% Al, Pb-62% Sn, and Al-33% Cu, are examined. For these alloys, high-purity grades and grades doped with impurities are tested. In addition, selected commercial superplastic alloys are included to examine the orientation of cavity stringers as a function of strain rate in light of a new mechanistic model proposed for the stringers. Also examined are the effects of major impurities, such as Cu and Mg, on cavitation and ductility behavior in two near-nano scale A1 alloys, which exhibit high strain rate superplasticity. An innovative technique employs flat double-shear specimens to simplify the test procedure and avoid problems associated with torsional and tensile loading. %%% The results of this program should have significant impact in the science and technology of metal alloy superplasticity. It will advance understanding of the processing of commercial superplastic alloys and could lead to improvements in the performance of these materials. ***