Sintering and Related Powder Processing Science and Technologies: Field Assisted Sintering and Other Novel Methods
Sponsored by: ACerS Basic Science Division, TMS Powder Materials Committee
Program Organizers: Wolfgang Rheinheimer, University of Stuttgart; Ricardo Castro, University of California, Davis; Zachary Cordero, Rice University; Eugene Olevsky, San Diego State University
Monday 8:00 AM
November 2, 2020
Room: Virtual Meeting Room 22
Location: MS&T Virtual
Session Chair: Wolfgang Rheinheimer, TU Darmstadt
8:00 AM Cancelled
Modification of Grain Boundary Core Structures by Applied Electric Fields: Klaus van Benthem1; Lauren Hughes1; Sean Russell1; 1University of California, Davis
Electric field applied during sintering can lead to accelerated densification and modified grain growth behavior. In this presentation we will review a systematic study of electric field effects on grain boundary core structures of (100) twist grain boundaries in SrTiO3. Grain boundaries diffusion bonded in the presence of an applied electrostatic field show an abrupt and atomically structured interface with an interface expansion of 0.43±0.03 nm. With increasing field strength during bonding an increasing number of oxygen vacancies appears randomly distributed in the vicinity of the grain boundary plane. In the absence of an applied electric field, however, the grain boundary core structure revealed a width of 0.89 ± 0.13 nm. Initial results for the direct measurement of space charge layers surrounding the grain boundary plane will be reviewed. This work was supported by the Army Research Office (W911NF-16-1-0394) and the National Science Foundation (DMR-1836571).
8:30 AM
Flash Sintering Solid State Ceramic Electrolytes Using a Novel Multi- electrode Approach: Gareth Jones1; Christopher Green2; David Pearmain2; Geoff West1; Emma Kendrick3; Claire Dancer1; 1University of Warwick; 2Lucideon Limited; 3University of Birmingham
Flash sintering (FS) is a promising new technology using electric fields to rapidly densify ceramics at reduced furnace temperatures. FS is of interest for the sintering of sensitive materials such as solid-state battery electrolytes, where volatilisation of charge carriers is a significant issue at conventional furnace temperatures. A key challenge for FS is hotspot formation, unavoidable for most geometries, leading to microstructural inhomogeneity. Here, a technical solution to this problem is presented using a multiple electrode approach, simultaneously driving three separate electrodes to homogenise the current distribution throughout a ceramic green. We show that the current distribution can be controlled using bespoke nonlinear controllers, which drive the electrodes according to appropriate temporal relationships. We demonstrate the viability of this approach by FS of the solid-state electrolyte sodium beta alumina, linking the processing conditions to the development of microstructural features.
8:50 AM Invited
Grain Growth Measurements of Anti-thermal Strontium Titanate with Non-destructive High Energy X-ray Diffraction Microscopy (HEDM): Amanda Krause1; He Liu2; Christopher Marvel3; Bryan Conry1; Michael Hoffmann4; Robert Suter2; Carl Krill5; Martin Harmer3; 1University of Florida; 2Carnegie Mellon University; 3Lehigh University; 4Karlsruhe Institute of Technology; 5Ulm University
Strontium titanate (SrTiO3) exhibits anti-thermal grain growth between 1350°C and 1425°C, where the grain boundary mobility decreases as the temperature increases. The underlying mechanism for this rare grain growth behavior is unknown. Previous grain growth studies show a change in the grain boundary character distribution within this temperature range. However, conventional grain growth studies rely on statistical comparisons of grain size distributions to describe grain growth and cannot capture the migration of individual grain boundaries or those of a specific energy or character. Here, the non-destructive microstructural characterization method high-energy x-ray diffraction microscopy (HEDM) is employed to directly correlate the velocity and character of individual SrTiO3 grain boundaries to elucidate anti-thermal behavior. Initial observations and the grain boundary velocity measurements at 1350°C (thermal regime) and 1400°C (anti-thermal regime) will be discussed.
9:20 AM
Electron Microscopy Observation of Electric Field Assisted Sintering of Stainless Steel Nanoparticles: Fei Wang1; Qin Zhou1; Xingzhong Li1; Michael Nastasi1; Bai Cui1; 1University of Nebraska Lincoln
The intrinsic role of electrical current on the electric field-assisted sintering (EFAS) process of stainless steel 316L nanoparticles has been revealed by both ex situ and in situ experiments. A novel device on the Si chip that has been designed and fabricated to fit into the sample holder of a transmission electron microscope for these experiments. The evolution of nanoparticle morphology and microstructures during the EFAS process has been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which has been combined with the simultaneous measurement of the electric voltage and current changes. A four-stage mechanism for the EFAS process of stainless steel 316L nanoparticles has been proposed based on these experimental investigations.
9:40 AM Invited
Selective Sintering Technique: Modeling and Experimentation: Elisa Torresani1; Geuntak Lee1; Eugene Olevsky1; 1San Diego State University
Additive manufacturing directly enables the production of complex-shape components. The downsides of the additive manufacturing technology such as the binder jetting is the necessity of conducting the complex and time-consuming debinding and the difficulty to achieve the full density of the components at the end of the sintering cycle. In the present work a novel sintering method to produce fully dense ceramic complex-shape components is presented. The proposed selective sintering technique combined with the powder bed 3D-Printing technology allows the fabrication of fully dense complex shape parts. The process is composed of four steps: 1) Fabrication of powder mold; 2) Injection of powder or slurry in the mold; 3) Isostatic pressing of the sacrificial mold and powder assembly; 4) Sintering. The possibility to design an optimal sintering cycle through a model and the advantages of this process regarding sinterability, grain size retention, short process time, and improved microstructure are discussed.
10:10 AM
Reduced Pressure Nanosintering during Environmentally Controlled – Pressure Assisted Sintering: Kevin Anderson1; James Wollmershauser1; Mason Wolak1; Boris Feigelson1; 1U.S. Naval Research Laboratory
Environmentally controlled – pressure assisted sintering (EC-PAS) has been utilized to produce fully dense nanocrystalline ceramics with grain sizes as small as 4 nm (MgAl2O4). Densification with negligible grain growth is enabled by the EC-PAS process through a combination of applied pressure (2 GPa), low temperatures (< 0.5 Tm), and the creation of pristine nanoparticle surfaces that are preserved through the sintering stage. Nanosintering with EC-PAS has been achieved at 2 GPa applied pressure across many materials systems including a variety of oxides and carbides. In an effort to expand the processing space of EC-PAS, nanosintering was performed at lower applied pressures by tuning other sintering parameters including temperature, heating and cooling rates, and soak times. The effect of these parameters on the grain size and density of sintered bodies will be discussed using MgAl2O4 as a model system.