Sintering and Related Powder Processing Science and Technologies: Advanced Sintering Techniques
Program Organizers: Wolfgang Rheinheimer, Purdue University; Zachary Cordero, Rice University; Ricardo Castro, University of California, Davis; Eugene Olevsky, San Diego State University

Wednesday 2:00 PM
October 2, 2019
Room: E142
Location: Oregon Convention Center

Session Chair: Eugene Olevsky, San Diego State University; Wolfgang Rheinheimer, Purdue University

2:00 PM  Invited
Cold Sintering of Ceramic Materials, Devices and Novel Nanocomposites: Clive Randall1; 1Penn State University
    Cold sintering enables a platform for better unification of material science. Now ceramics, metal and polymers can be processed under a common platform in one step processes. With controlling the forming process new nanocomposites can be fabricated. Polymers, gels and nanoparticulates can be dispersed, interconnected and sintered in the grain boundaries of a ceramic matrix phase. With the ability to sinter metal phases, multilayer devices can be co-sintered with electrodes made from metals such as Al, Ag, Fe and Cu. With appropriate binder selection, polypropylene carbonate and its de-binding at 130° C we can remove organic binders and leave metals and other more stable polymers within the layers that then can be co-sintered under the cold sintering process and form unique combinations of materials in multilayers. This then could lead to new devices and devices that can impact important products that are required for a more sustainable economy.

2:30 PM  Invited
Controlling Factors in Flash Sintering of Ceramics: Richard Todd1; Wei Ji2; Zhengyi Fu3; Yinsheng Li1; Yasuhiro Kubota1; Andrew Gibson1; 1University of Oxford; 2University of Oxford/Wuhan University of Technology; 3Wuhan University of Technology
    The investigation of flash sintering has led to intensive investigation of the effects of electric fields on the sintering of ceramics. This presentation examines which mechanisms are primarily responsible for the increase of electrical power dissipation and rapid sintering involved. Data from a wide range of ceramics shows that the apparent resistivity-temperature relationship is sufficient to explain the onset of flash sintering. In some cases, this relationship reflects the innate conductivity of the ceramic, but in others concurrent sintering, changes in defect structure and phase changes play a role. In the case of densification, it is shown that YSZ can be sintered on a similar timescale to flash sintering, but without the use of an electric field, provided the heating rate is rapid. Microstructures from different heating rates are compared with a view to understanding the micromechanisms responsible. Evidence from the flash sintering of SiC is also described.

3:10 PM  
Staged Microstructural Study of Flash Sintered Titania: Xin Li Phuah1; Han Wang1; Harry Charalambous2; Shikhar Jha2; Jin Li1; Thomas Tsakalakos2; Xinghang Zhang1; Haiyan Wang1; 1Purdue University; 2Rutgers University
    Flash sintering offers more control of microstructure owing to its additional sintering conditions compared to conventional sintering, including electric field, current density limit and holding time. A systematic study of flash sintered TiO2 is presented to investigate the effects of flash sintering conditions on the asymmetrical microstructure and defect structure across the two electrodes of the samples. Grain growth has been found to be more prominent near the positive electrode and significantly influenced by the current density limit. Extended defects, including dislocations and stacking faults, have been observed near the positive electrode due to the generation and coalescence of oxygen vacancies by the electric field. The generation of defects is highly dependent on the strength of electric field and the defect density decreases with additional grain growth under a longer holding time.

3:30 PM Break

3:50 PM  
Room Temperature Plasticity in Flash-sintered TiO2: Jin Li1; Jaehun Cho1; Jie Ding1; Harry Charalambous2; Sichuang Xue1; Han Wang1; Xin Li Phuah1; Thomas Tsakalakos2; R. Edwin García1; Amiya K. Mukherjee3; Noam Bernstein4; C. Stephen Hellberg4; Haiyan Wang1; Xinghang Zhang1; 1Purdue University; 2Rutgers University; 3University of California, Davis; 4U.S. Naval Research Laboratory
    Ceramic materials have been widely used for structural applications. However, most ceramics have rather limited plasticity at low temperatures. A majority of ceramics fracture well before the onset of plastic yielding. The brittle nature of ceramics arises from the lack of dislocation activity and the need for high stress to nucleate dislocations. Here we have investigated the deformability of TiO2 prepared by a flash-sintering technique. Our in situ studies show that the flash sintered TiO2 can be compressed to ~ 10% strain under room temperature without noticeable crack formation. Distinct deformation behaviors have been observed in flash-sintered TiO2 deformed at different testing temperatures, ranging from room temperature to 600°C. Potential mechanisms that may render ductile ceramic materials are discussed.

4:10 PM  
Analysis of SPS Parameters and Resultant Electrical Response of SPS Sintered Specimens: Rosario Gerhardt1; Thomas Rudzik1; 1Georgia Institute of Technology
    A thorough understanding of the underlying mechanisms of spark plasma sintering has been difficult to achieve due to the many processing parameters which can affect the sintering process. Conflicting results point to the various parameters. It has also been difficult to determine what effects changing a single parameter have on the final microstructure and properties of the sintered sample because many of these parameters are interdependent and often not reported. Through the detailed analysis of electrical conditions used during the SPS process of a series of samples, as well as measurements of the ac impedance response and equivalent circuit fitting of the resulting samples, it is shown that a wide array of information regarding the microstructural evolution during sintering can be revealed. The results show the unexplored potential of electrical characterization for understanding the sintering process and for elucidating the effects of processing parameters on the resulting microstructure and properties.