Effects of Point Defects on Dislocation Nucleation in Metals

传统的强化材料的方法通常集中于通过降低位错迁移率来增加对塑性变形的抵抗力。在许多快速发展的金属材料中，表现出增强的强度，例如多层金属和超细晶粒金属，限制因素可能是位错的产生和增殖，而不是位错的运动。虽然世界各地的许多团体在这一主题上进行了大量的工作，但大多数研究都集中在原始或极端受控的结构上，而大多数工程合金是复杂的多组分系统，具有普遍的缺陷结构。暴露于辐射和现有的非平衡处理特别可能产生过量空位和其他点缺陷。本计画将利用实验与计算研究，提供金属中具有广泛缺陷结构之源位错之成核与运作之基础研究。该团队将通过实验量化空位，杂质和晶界对位错成核和塑性的影响，在极端应力下，在各种金属系统中使用压痕技术来探测塑性的开始。点缺陷浓度将通过正电子孔隙率测定法进行评估。纳米压痕研究也将被用来证明现有的缺陷在纳米级的位错在高应力下的传播的影响，这些结果将使用分子静力学和动力学的计算模拟进行比较。这种耦合将通过发展多尺度建模技术来解决长度和时间尺度问题，从而在初期塑性的计算模型和实验研究之间建立更强的关系。非技术性总结在工程师和科学家用于强化金属材料的许多方法中，越来越强调开发表现出"越小越强“范例的纳米级结构，其中在材料中具有较小的长度尺度提供了更大的变形阻力。该项目将侧重于确定金属中现有缺陷对塑性开始的基本影响。将有一个实验部分，其中塑性的开始是在各种金属材料中测量，以量化材料的极限强度。这些结果将进行比较，以解决时间和长度尺度的问题，在建模的永久变形的发病计算模拟。支持的研究生将与一组材料科学和工程本科生合作，他们为初中生开发了一套材料，并将在组织工程学生团队和向该地区数十个服务不足的教室分发材料方面获得经验。

TECHNICAL SUMMARYTraditional methods of strengthening materials often focus on increasing the resistance to plastic deformation by decreasing dislocation mobility. In many of the rapidly developing metallic materials that exhibit enhanced strengths, such as multilayered metals and ultrafine grained metals, the limiting factor is likely the creation and multiplication of dislocations, rather than the motion of dislocations. While there is substantial work on this topic by many groups around the world, most studies focus on pristine or extremely controlled structures, whereas most engineering alloys are complex, multicomponent systems that have prevalent defect structures. Exposure to radiation and existing non-equilibrium processing is particularly likely to generate excess vacancies and other point defects. This project will provide a fundamental study of the nucleation of and operation of sources dislocations with a wide range defect structures in metals using both experimental and computational studies. The team will experimentally quantify the impact of vacancies, impurities, and grain boundaries on dislocation nucleation and plasticity at extreme stresses in a variety of metallic systems using indentation techniques to probe the onset of plasticity. Point defect concentration will be assessed by positron porosimetry. Nanoindentation studies will also be used to demonstrate the impact of existing defects on the propagation of dislocations at the nm scale at high stresses, and these results will be compared to computational simulations using both molecular statics and dynamics. This coupling will develop stronger relationships between computational models of incipient plasticity and experimental studies through the development of multi-scale modeling techniques addressing both length and time scales.NON-TECHNICAL SUMMARYOf the many methods used by engineers and scientists to strengthen metallic materials there is increased emphasis on developing nanoscale structures that exhibit the -smaller is stronger- paradigm, where having a smaller length scale in the material provides more resistance to deformation. This project will focus on determining the fundamental effects of existing defects in metals on the onset of plasticity. There will be an experimental component, wherein the onset of plasticity is measured in a variety of metallic materials to quantify the ultimate strength of the material. These results will be compared to computational simulations developed to address both time and length scale issues in modeling the onset of permanent deformation. The graduate students supported will be partnered with a group of materials science and engineering undergraduates that have developed an outreach kit of materials for junior high students, and will gain experience in organizing teams of engineering students and distributing the kits to dozens of underserved classrooms around the region.