Prediction and Control of Tungsten and Titanium Dioxide Sintering and Processing

烧结，或通过烧制将粉末固化成有用的零件，是最古老和最常用的材料加工和制造方法之一。然而，控制烧结机制的物理过程尚不清楚。该奖项以钨和二氧化钛作为初始模型系统，支持烧结和材料加工的基础研究。从这项研究中产生的知识将有助于预测和控制结构合金和功能陶瓷的制造过程，应用于能源，航空航天，汽车和其他行业。教育和外展活动与研究相结合，以激励和指导不同层次的学生，同时通过吸引不同背景和代表性不足的群体的学生来促进教育的多样性。本项目旨在实现对固态活化烧结现象的基本理解。半个多世纪以来，人们已经知道，添加少量的某些烧结助剂可以帮助大幅提高固态的致密率，类似于众所周知的液相烧结现象。然而，这种所谓的“固态活化烧结”的确切机制尚不完全清楚。最近的一系列研究表明，这种现象是由于助烧诱导的（基）、预熔样、颗粒间膜的质量输运增强，这些膜的热力学稳定在体固相线以下。使用钨和二氧化钛作为金属和陶瓷系统的初始模型，通过烧结实验、材料表征和热力学建模的结合，实现了对这种现象的基本理解。此外，本文还提出了一种新型的λ图，并对其进行了进一步的扩展，以预测高温下多晶材料中一般晶界无序的热力学趋势；这种图可以用来预测烧结行为，以及其他材料的制造、加工和性能。

Sintering, or consolidating powders to useful parts by firing, is one of the oldest and most commonly-used materials processing and fabrication methods. Yet, much is unknown about the physical processes that control sintering mechanisms. Using tungsten and titanium dioxide as the initial model systems, this award supports fundamental research of sintering and materials processing. The knowledge generated from this research will help to predict and control the fabrication processing of both structural alloys and functional ceramics, with applications in energy, aerospace, automotive, and other industries. Education and outreach activities are integrated with the research to inspire and mentor students at various levels, while promoting education diversity by engaging students with different backgrounds and underrepresented groups.This project aims to achieve fundamental understandings of the solid-state activated sintering phenomenon. It has been known for more than half a century that adding a small amount of certain sintering aids can help to substantially enhance the densification rates in the solid state, similar to the well-understood phenomenon of liquid-phase sintering. However, the exact mechanism for this so-called "solid-state activated sintering" is not fully understood. A series of recent studies suggests that this phenomenon is due to enhanced mass transport in the sintering-aid induced (based), premelting-like, intergranular films that are thermodynamically stabilized below the bulk solidus lines. Using tungsten and titanium dioxide as the initial model metallic and ceramic systems, fundamental understandings of this phenomenon are achieved via a combination of sintering experiments, materials characterization, and thermodynamic modeling. Furthermore, a novel type of lambda-diagrams are developed and further extended to predict the thermodynamic tendency for general grain boundaries in polycrystalline materials to disorder at high temperatures; such diagrams can be used to forecast sintering behaviors, as well as other materials fabrication processing and properties.