The Role of Impurities in Superplastic Deformation and Cavitation

小行星9810422 本研究的重点是金属合金的超塑性流动的亚结构的细节，特别侧重于超塑性区域（区域II）。 这包括对选定类型的杂质原子对超塑性流动和空化的影响的系统检查。 这样的检查解决了各种杂质之间的协同相互作用对空化和延展性的影响。 杂质类型和水平的空化过程的影响进行了深入的研究，着眼于空穴成核和变形和空穴生长之间的关系。 杂质分布在边界的特点。 与超塑性变形（边界滑动和迁移，晶粒形状，晶粒旋转，和韧带）的微观结构的细节被确定为杂质水平和类型，大应变（30%），和变形模式（拉伸和双剪切）的函数。 三种不同的模型材料，Zn-22%Al，Pb-62%Sn，和Al-33%Cu进行了检查。 对于这些合金，测试高纯度等级和掺杂杂质的等级。 此外，选定的商业超塑性合金包括检查作为应变率的函数的腔纵梁的方向在一个新的力学模型提出的纵梁。 还研究了主要杂质，如Cu和Mg，在两个近纳米级的A1合金，表现出高应变速率超塑性的空泡和延性行为的影响。 一项创新技术采用扁平双剪切试样，以简化测试程序，避免与扭转和拉伸载荷相关的问题。 该项目的研究成果将在金属合金超塑性科学技术领域产生重大影响。 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. ***