Determining Grain Boundary Solute Segregation Specificity in Nanocrystalline Stability

非技术摘要：当材料的晶粒尺寸减小时，材料的强度增加。不幸的是，与较大尺寸的晶粒相比，这些小晶粒尺寸在能量上是不利的。在加热时，较小的晶粒将生长以减少这种能量差，从而导致强度损失。近年来，特定类型合金的发展表明，较低浓度的原子类型或溶质可以稳定这些晶粒，防止这种生长。这些观察的结果是各种模型来解释晶粒尺寸的稳定。然而，这些模型有几个基本的科学差距仍然有待解决。例如，模型化的晶界被认为是等效的，其中实际晶界在其结构、能量和迁移率方面是不同的。缺乏实验验证这种溶质特定偏析晶界阻碍了进一步的模型开发。这项研究将克服这些限制，结合电子显微镜和原子探针断层扫描检测溶质偏析到这些特定的边界。然后，这些结果将被前馈到解释这种行为多样性的原子模型。这项研究将被纳入各种推广活动，包括为中学教师举办的夏季材料夏令营，将材料科学引入初中/高中课堂。技术摘要：纳米晶体材料是一个活跃的研究领域，由于其独特的尺寸依赖性能。由于界面（边界）构成整个结构的很大一部分，来自这些边界的相应界面能可以使这些晶粒固有地不稳定。溶质分配到这些边界已被设计为一种手段，以稳定这些晶粒对增长的动力学溶质拖曳效应和热力学减少的界面能的概念被建议的机制稳定。到目前为止，这些模型假设所有的晶界是各向同性的，彼此等效;在现实中，晶界是不同的能量，结构和流动性与溶质分区是该可变性的函数。利用交叉相关旋进电子衍射和原子探针层析成像，本研究将阐明溶质对晶界的特异性，导致稳定。实验结果将被链接到氢化物蒙特卡洛分子动力学原子模型，将阐明稳定到特定的边界类型的机制。 此外，将测量退火期间这些边界的实时实验定量，以确定稳定性的迁移率和动力学贡献者。集体的结果将桥梁突出的和基本的知识差距，揭示如何热力学和动力学考虑特定的晶界导致晶粒尺寸的稳定性。这项研究将无缝集成到各种推广活动，以加强STEM学科，包括为中学教师举办的夏季材料夏令营，将材料科学引入初中/高中课堂。

Non-technical Abstract: When the grain size of a material is reduced, the strength of a material increases. Unfortunately, these small grain sizes are energetically unfavorable as compared to larger sized grains. Upon heating, the smaller grains will grow to reduce this energy difference which results in the loss of strength. In recent years, the development of specific types of alloys has shown that the lower concentration atom type, or solute, can stabilize these grains against this growth. An outcome of these observations has been various models to explain the grain size stabilization. However, these models have several fundamental scientific gaps that still remain to be solved. For example, the modeled grain boundaries are considered equivalent wherein reality grain boundaries are diverse in their structure, energy, and mobility. The lack of experimental verification of this solute specific segregation to grain boundaries has hindered further model development. This research will overcome these prior limitations by combining electron microscopy and atom probe tomography to detect solute segregation to those specific boundaries. These results will then be forward fed to atomics models that explain this diversity of behavior. This research will be integrated into various outreach activities, including a summer materials camp for secondary education teachers to introduce materials science into the middle/high school classrooms. Technical Abstract:Nano-crystalline materials is an area of active research owing to their unique size dependent properties. Since interfaces (boundaries) constitute a large fraction of the entire structure, the corresponding interfacial energy from those boundaries can make these grains inherently unstable. Solute partitioning to these boundaries has been devised as a means to stabilize these grains against growth with concepts of kinetic solute drag effects and thermodynamic reduction of interfacial energy being suggested mechanisms for stabilization. To date, these models assume all the grain boundaries are isotropic and equivalent to each other; in reality grain boundaries are diverse in energy, structure, and mobility with solute partitioning being a function of that variability. Using cross-correlative precession electron diffraction and atom probe tomography, this research will elucidate the solute specificity to grain boundaries that leads to stabilization. The experimental findings will be linked to hydride Monte Carlo-Molecular Dynamics atomistic models that will elucidate the mechanisms of stabilization to specific boundary types. In addition, real-time experimental quantification of those boundaries during annealing will be measured to ascertain mobility and kinetic contributors to stability. The collective results will bridge outstanding and fundamental knowledge gaps in revealing how thermodynamic and kinetic considerations for specific grain boundaries leads to grain size stability. This research will be seamlessly integrated to various outreach activities to strengthen the STEM disciplines including a summer materials camp for secondary education teachers to introduce materials science into middle/high school classrooms.