Prediction and Control of Tungsten and Titanium Dioxide Sintering and Processing

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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.