Manipulation of Grain Boundary Structures by Electric Fields

非技术描述：在用于制造应用的陶瓷加工过程中施加电偏压有可能显著缩短加工时间、降低所需温度和降低所需机械压力。这些陶瓷的这些工艺改进的机理尚不清楚；这项研究正在揭示潜在的原因。本研究的实验工作以理论建模为补充。这项研究的预期结果是告知如何利用电场来改善现有材料的加工条件，并定制新的功能陶瓷材料。研究生和本科生正在接受材料科学和工程领域的培训，为以后在学术界或高科技制造领域的职业生涯做准备。参与活动的大学生正在指导传统上代表人数较少的社区的高中生，以提高科学素养和大学入学率。技术细节：电场辅助烧结已经证明了加速粉末压坯致密化、降低加工温度和抑制颗粒长大的可行性。然而，在没有电流流动的情况下，电场的作用仍然是未知的。一个主要的挑战是系统地研究纳米晶陶瓷中由于大量随机取向的普通晶界而出现的缺陷结构。利用自行设计的扩散连接装置，系统地研究了原子和电子晶界结构随外加电场强度、方向和晶界几何形状的变化。这种实验方法允许将特定选择的晶界几何形状作为外加电场的函数进行比较，并阐明外加电场是否影响晶界的热力学稳定性。实验得到了基于晶界核内原子密度变化的新的建模例程的补充。结合扩散连接、原子分辨率表征和界面热力学状态的理论模型，对电场对晶界形成的影响进行了定量的机理理解。现场辅助修改晶界网络预计将成为一种颠覆性技术，用于定制具有前所未有的宏观物理特性的新微结构。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION: The application of an electrical bias during ceramic processing for manufacturing applications has the potential to dramatically improve processing times, lower required temperatures, and decrease required mechanical pressures. The mechanisms for these process improvements of these ceramics is unclear; this research is revealing the underlying reasons. The experimental work in this study is complemented by theoretical modeling. The anticipated results of this study are informing how electric fields can be utilized for enhancing processing conditions for existing materials, and tailoring of new functional ceramic materials. Graduate and undergraduate students are being trained in areas of materials science and engineering for subsequent careers in academia or fields of high-tech manufacturing. Participating university students are mentoring high school students from traditionally underrepresented communities to improve science literacy and college-going rates.TECHNICAL DETAILS: Electric field assisted sintering has demonstrated the feasibility to accelerate densification of powder compacts, lower processing temperatures, and suppress grain growth. The role of electric fields in the absence of current flow remains, however, mostly unknown. A major challenge is the systematic investigation of emerging defect structures in nanocrystalline ceramics due to the overwhelming number of randomly oriented general grain boundaries. Diffusion bonding of bicrystals in a custom-built setup is used to systematically investigate atomic and electronic grain boundary structures as a function of applied field strength, direction, and grain boundary geometry. This experimental approach allows the comparison of specifically selected grain boundary geometries as a function of the applied electric field, and elucidates whether externally applied electric fields impact on the thermodynamic stability of grain boundaries. Experiments are complemented by novel modelling routines that are based on variations of atomic density within the grain boundary cores. The combination of diffusion bonding, atomic resolution characterization, and theoretical modelling of the interfacial thermodynamic state is used to gain a quantitative mechanistic understanding of electric field effects on grain boundary formation. Field-assisted modifications of grain boundary networks are expected to become a disruptive technology for tailoring of new microstructures with unprecedented macroscopic physical properties.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.