Journal of the American Ceramic Society Awards Symposium: JACerS Award Symposium Session II
Program Organizers: William Fahrenholtz, Missouri University of Science and Technology

Wednesday 2:00 PM
October 2, 2019
Room: A107
Location: Oregon Convention Center

Session Chair: William Fahrenholtz, Missouri University of Science and Technology

2:00 PM  Invited
Electronic Structure and Mechanical Properties of a Large Realistic Model of Inter-granular Glassy Film in β-Si3N4: Wai-Yim Ching1; 1University of Missouri
    Based on a large periodic model containing two grains of β-Si3N4 with different orientations and two IGFs, the electronic structure, density of states, interatomic bonding, partial charge distribution are obtained and analyzed focusing on the interfacial regions. The total bond order density (TBOD), a quantum mechanical metric, is evaluated in different interfacial and bulk regions to reveal the subtle differences in the interfacial cohesion. Moreover, the mechanical properties of this IGF model are calculated using a stress vs strain approach showing the effect of a less rigid glassy layer. These results are compared with parallel calculations on crystalline α-Si3N4, β-Si3N4 and Si2N2O and their mechanical properties. The insights obtained from these detailed DFT calculation and analysis are discussed in the broader context of implications on the strength, fracture toughness, failure behavior and processing methods for nanoscale materials.

2:30 PM  Invited
High-strength, Light-weight and Printable Ceramic Foams with Hierarchical Pore Structure from Boehmite Foams: Xiaoyan Zhang1; Wenlong Huo1; Yugu Chen1; Jinlong Yang1; 1Tsinghua University
     Porous ceramics with high strength and hierarchical structure are increasingly attractive materials. We herein report novel ceramic foams from boehmite gel foams, which exhibit both high porosity and unprecedentedly high strength. The boehmite gel foams are prepared by mechanical frothing boehmite aqueous suspension to make colloidal foams with uniform and tiny bubbles, followed by gelation through tailoring pH or increasing ions strength. The obtained alumina foams possess uniform macro-pores with tailorable size in the range of 4~70 m and nanoscale pores in cell wall after sintering at 1200-1300C, which is a much lower in comparison to normal sintering temperature of alumina ceramics. The foams exhibit the highest strength to the best of our knowledge, which is attributed to the tiny grains, large amount of grain boundaries, uniform pores and hierarchical pore structure. The foams sintered below 1200C have unprecedentedly specific surface area of 200-300 m2/g. In addition, the gel foams show excellent printability due to its ultra-stability, high yield stress and storage moduli, which allow for the fabrication of lightweight and complex-shape materials. We believe this new foam materials has potential to be applied in several fields, for example, construction, thermal insulation, filtration, adsorption, aerospace, and so on.

3:00 PM  Invited
Thermochemical Model on the Carbothermal Reduction of Oxides During Spark Plasma Sintering of Zirconium Diboride: David Pham1; J Dycus2; James LeBeau2; Krishna Muralidharan1; Venkateswara Rao Manga1; Erica Corral1; 1The University of Arizona; 2North Carolina State University
     Carbon was used to reduce oxides in spark plasma sintered ZrB2 ultra-high temperature ceramics. A thermodynamic model was used to evaluate the reducing reactions to remove B2O3 and ZrO2 from the powder. Powder oxygen content was measured and carbon additions of 0.5 wt% and 0.75 wt% were used. A C-ZrO2 pseudo binary diagram, ZrO2-B2O3-C pseudo ternaries and Zr-C-O potential phase diagrams were generated to show how the reactions can be related to an open system experiment in the tube furnace. Scanning transmission electron microscopy identified impurity phases composed of amorphous Zr-B-O with lamellar BN and a Zr-C-O ternary model was calculated under SPS sintering conditionsat 1900 C and 6 Pa to understand how oxides can be retained in the microstructure.

3:30 PM Break

3:50 PM  Invited
The Future of Grain Boundary Complexion Engineering: Amanda Krause1; Patrick Cantwell2; Christopher Marvel3; Charles Compson4; Jeffrey Rickman3; Martin Harmer3; 1University of Florida; 2Rose–Hulman Institute of Technology; 3Lehigh University; 4Almatis, Inc
    Grain boundaries obtain equilibrium structures, known as complexions, that undergo first-order transitions. Over the past decade, grain boundary complexions and their transitions have been identified in different material systems, where they influence many material behaviors, including grain growth, fracture toughness, ductility, creep resistance, ionic conductivity, and radiation-resistance. The goal for grain boundary complexion engineering (GBCE) is to understand and use the grain boundary’s structure-property relationship to control bulk material performance. The increase in grain boundary simulations and availability of advanced characterization techniques has led to the creation of thermodynamic complexion diagrams and time-temperature transformation curves to aid GBCE. However, we still lack mechanistic understanding because of challenges in identifying complexions and isolating their transition events. Additionally, many different grain boundaries types can co-exist in a structure, which can obscure the role of a single complexion. Here, we discuss the critical questions and potential data method approaches to enable GBCE.

4:20 PM  Invited
Fabrication and Properties of Transparent Nd-doped BaF2 Ceramics: Yiquan Wu1; Jianlin Li2; Xianqiang Chen1; 1Alfred University; 2Hainan University
    Fluoride transparent ceramics have been known for several decades, with the first reports of fluoride optical ceramics in the context of laser materials being investigations of metal fluorides performed by Eastman Kodak. Unfortunately, to the best of our knowledge, no reports of highly transparent Nd-doped BaF2 ceramics exist in the literature; an issue which this report is intended to address. Nd doped BaF2 nanoparticles have been prepared via co-precipitation and a pumping filtration wash method. The resulting submicron-scale powders were subsequently calcined at 600 C and then consolidated by vacuum sintering to produce Nd doped BaF2 ceramics with 5 and 10at.% Nd dopant. The phase composition and morphology of the synthesized nanoparticles were investigated by X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM) analyses, respectively.

4:50 PM  Invited
New Advanced Sintering Approaches Based on Spark Plasma Sintering: Charles Maniere1; Geuntak Lee2; Elisa Torresani2; Claude Estournes3; Eugene A. Olevsky2; 1Laboratoire CRISMAT; 2Powder Technology Laboratory; 3CIRIMAT
    Spark plasma sintering (SPS) combines high-pulsed electrical current, pressures and vacuum; these conditions allow lowering the sintering temperatures and are very interesting for advanced materials. In this presentation, I will show how SPS represents an even broader prospect and can be applied to complex shapes, larger scale/energy efficient configurations and also applied to the flash (ultra-rapid) sintering of nearly all materials. I will also present the advanced Multiphysics simulation tool we develop to study all previously cited approaches. These simulations include the Joule heating coupled with the sintering/grain growth kinetics through the “continuum theory of sintering”.

5:20 PM  Invited
Sintering Forces Acting among Particles during Sintering by Grain Boundary/Surface Diffusion: Fumihiro Wakai1; Gaku Okuma1; Norimasa Nishiyama1; Olivier Guillon2; 1Tokyo Institute of Technology; 2Research Center Juelich
    The microscopic principle of the stress-assisted sintering is that the relative velocity between two adjoining particles is proportional to the sum of the sintering force and the mechanical force transmitted by the contact. Here, we simulated sintering of four particles by coupled grain boundary diffusion and surface diffusion, in order to analyze how the sintering force varies with the evolution of particle shape, i.e., pinch-off of pore channel, formation and shrinkage of a closed pore. The shrinkage rate of the pore volume was proportional to the relative velocity of particles, then, to the sintering force. We discussed the effect of mechanical stress on sintering also.

5:50 PM  Invited
Sinter-cracking: Simulations and Experiments: Joseph Carazzone1; Michael Bonar2; Henry Baring1; Mark Cantu1; Zachary Cordero1; 1Rice University; 2U.S. Army Research Laboratory
    Additive manufacturing (AM) enables production of geometrically complex objects not easily attained by traditional means. Low-cost AM techniques like binder jetting rely on post-process sintering to achieve final properties, but encounter problems with distortion and cracking. In this work we seek to understand how stress concentration in complex AM geometries leads to cracking during sintering, with the goal of mitigating the problem. Experiments involving in situ analysis of 3D-printed samples during sintering reveal how sinter-cracks initiate and grow, revealing unexpected behavior. Discrete element simulations offer further insight by allowing direct measurement of the stresses in a sinter-cracking material. We find that sinter-cracking phenomena correspond well with creep-cracking in dense materials, and that the net section stress both characterizes the stress field and correlates with the rate of sinter-crack growth. Knowledge of the correct fracture mechanics parameter will enable development of processing regimes that avoid sinter-cracking, resulting in quality AM products.