Manufacturing and Processing of Advanced Ceramic Materials: Processing of Oxide Ceramics
Sponsored by: ACerS Manufacturing Division
Program Organizers: Bai Cui, University of Nebraska Lincoln; Mike Alexander, Allied Mineral Products, Inc.; Eric Faierson, Quad City Manufacturing Laboratory - Western Illinois University; James Hemrick, Oak Ridge National Laboratory; Keith DeCarlo, Blasch Precision Ceramics
Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 16
Location: MS&T Virtual
Session Chair: William Carty, Alfred University; Keith DeCarlo, Blasch Precision Ceramics
2:00 PM Invited
Investigating the Dependence of Microstructure Evolution in Alumina on the Liquid Phase Chemistry in the CaO-Al2O3-SiO2 System: Densification, Grain Growth and Secondary Phase Formation: Sarah Whipkey1; William Carty1; 1Alfred University
This study investigated microstructure evolution of industrial-grade alumina (88-98%) with grain boundary compositions in the CaO-Al2O3-SiO2 system. The SiO2:CaO ratio strongly influenced both densification and grain size under identical sintering conditions. Densification and grain growth behavior was categorized into three distinct regions by the SiO2:CaO ratio, proposed to be due to varying viscosities, diffusion rates, and glass forming tendencies. Chemistries with molar ratios of SiO2:CaO > 1 (high silica) exhibited predictable sintering behavior, with minimal secondary phase formation, whereas SiO2:CaO < 1 (high calcia) displayed significant secondary phase formation, which inhibited the growth of alumina grains and reduced grain sizes. Systems with SiO2:CaO ≈ 1 exhibited unpredictable behavior and secondary phase formation, presumably due to non-uniform chemistry distributions. Normal grain growth was observed in all cases, and average grain sizes increased with increasing CaO content until the SiO2:CaO ratio fell below 1:1.5, where excessive secondary phase formation occurred.
2:40 PM Invited
Opportunities for Tailored Grain Boundary Networks in Thermomagnetically Processed Alumina Ceramics: Amanda Krause1; Bryan Conry1; Michael Kesler2; 1University of Florida; 2Oak Ridge National Laboratory
Textured microstructures are often associated with unique grain boundary character distributions (GBCD) and grain boundary networks that can improve bulk material behaviors, including corrosion resistance and fracture toughness. Thermomagnetic processing is an opportunity to create textured grains and, thus, preferred GBCD in polycrystalline ceramic monoliths, which are otherwise limited by the random nature of powder processing. We investigate how magnetically-induced textures affect the GBCD and grain boundary networks in α-alumina. Alumina slips are cast in a magnetic field of various strengths and subsequently sintered and annealed at high temperatures (1400-1600°C). The GBCD and grain boundary network are evaluated via serial sectioning in a dual beam focused ion beam/scanning electron microscope with electron backscattered diffraction (EBSD). The ramifications for tailoring GBCD and grain boundary networks in bulk ceramics will be discussed.
3:20 PM
Self-bonded Refractories for Investment Casting Mold Manufacture: David Price1; 1IC Ceramic Consulting, LLC
Self-Bonded Refractory, Patent #15/795,5573, utilizes a colloidal alumina binder between 72 and 96 % Al2O3. X-ray Diffraction Analysis confirms the binder phase in Self-Bonded Refractory consists of crystalline aluminum oxide, alpha, theta, and kappa phases with minimal amorphous phase, and with not more than 1.2% crystalline silica. Self-Bonded Refractory binder is 25% the volume and 20% of colloidal silica sol and is a fully powder-based refractory system, just add water. Self-Bonded Refractory has a firing range between 1,100 and 1,200 deg. C and Cold Fired MOR of 368 psi, sufficient and suitable for precision metal casting. The green elastic modulus of Self-Bonded Refractory, measured by Dynamic Modulus Analysis (DMA), is 10 times lower compared to colloidal silica-bonded systems. High temperature Creep resistance is 10 times greater with Self-Bonded Refractory, and in contact with Titanium 6Al 4V Self-Bonded Refractory did not show the reaction typical of a colloidal silica-bonded mold.
3:40 PM Invited
Fabricating Alumina with Heterogeneous Microstructure Using Integrated Additive/Subtractive Manufacturing (IASM): Xiao Geng1; Jincheng Lei1; Shenglong Mu1; Hai Xiao1; Jianhua Tong1; Rajendra Bordia1; Fei Peng1; 1Clemson University
Fabricating ceramics with heterogeneous microstructure enables novel properties of materials. To precisely control the ceramic’s microstructure, we build a system of integrated additive/subtractive manufacturing (IASM). In this system, we use the picosecond (PS) laser for localized micromachining, and a CO2 laser for selective sintering at precisely controlled positions. We demonstrate the approach of laser sintering of alumina with “brick-mortar” structure. After extrusion of each layer, a PS laser was used to create a pattern in this layer. A CO2 layer was then used to sinter this layer. The “brick-mortar” structure was thus achieved layer-by-layer. The PS laser patterning not only creates the unit cells in each layer, but also releases the stress during the CO2 laser sintering, resulting in crack-free unit cells. With the control of CO2 layer power and scanning speed, we can control the density gradient along the vertical direction and bonding between the layers.
4:20 PM
Optimized Etching of Porcelain and Polycrystalline Alumina with a Glass Phase: Sarah Whipkey1; Max Modugno1; Hyojin Lee1; William Carty1; 1Alfred University
Chemical and thermal etching are commonly used to enhance ceramic microstructural features for microscopy. While traditional etching conditions for these methods are sufficient for high purity ceramics, literature recommended conditions may not be applicable when significant glass is included. Porcelain and industrial alumina (Al2O3) contain measurable amounts of glass (~4-20 vol% in Al2O3 and 40-60 vol% in porcelain), and the chemistries of these glasses are proposed to be similar (silica-rich). Chemical etching porcelain is common, but published images are frequently over-etched, leading to erroneous interpretations of the role of quartz. Chemical etching was observed to be sensitive to residual stress in the glass, becoming more aggressive when in tension. For industrial Al2O3, thermal etching often initiated recrystallization of the grain boundary glass. To prevent this from altering and obscuring microstructures, combined chemical and thermal etching are proposed to prepare industrial Al2O3 for grain size measurements and to potentially assess porosity.