Role of Impurities in Superplastic Flow and Cavitation

9500316穆罕默德这是对细晶材料中超塑性流动和空化的基础研究。主要目的是评估低应力下的超塑性流动特性是否是杂质原子在晶界偏聚的结果，并解决有关中应力下超塑性变形和空化的亚结构细节和起源的几个问题。实验方法包括：(A)深入研究杂质类型和水平对空化过程的影响；(B)表征变形前后晶界上的杂质分布；(C)调查与超塑性变形有关的微观结构细节(晶界滑动和迁移、晶粒形状、晶格旋转、韧带和晶格位错)作为杂质水平和类型、应变和变形、模式(拉伸和双剪切)的函数；以及(D)研究使用反应雾化和沉积新工艺将氧化物分散固体引入超塑性合金对蠕变行为和组织的影响。使用了三种不同的模型材料，锌-22%铝、铅-62%锡和铝-33%铜，并控制了杂质的量。该项目不仅将加深对杂质原子在超塑性合金变形和断裂过程中作用的理解，还将为控制超塑性流动的变形过程的起源提供新的见解。***

9500316 Mohamed This is a fundamental investigation of superplastic flow and cavitation in fine-grained materials. The main objective is to assess if the characteristics of superplastic flow at low stresses are a consequence of impurity atom segregation at boundaries and to address several issues regarding the substructure details and origin of superplastic deformation and cavitation at intermediate stresses. The experimental approach involves: (a) an in-depth study of impurity type and level on the cavitation processes; (b) a characterization of impurity distribution at boundaries before and after deformation; (c) an investigation of microstructural details associated with superplastic deformation (boundary sliding and migration, grain shape, grain rotation, ligaments, and lattice dislocations) as a function of impurity level and type, strain, and deformation, mode (tension and double shear); and (d) an examination of the effects on creep behavior and microstructure of introducing oxide dispersoids into a superplastic alloy using the new process of Reactive Atomization and Deposition. Three different model materials, Zn-22%Al, Pb-62%Sn, and Al-33%Cu, are used with controlled amounts of impurities. %%% This project will not only enhance the understanding of the role of impurity atoms in the deformation and fracture of superplastic alloys, but also provide new insights into the origin of deformation processes controlling superplastic flow. ***