Ceramic Matrix Composites: CMC I
Sponsored by: ACerS Engineering Ceramics Division
Program Organizers: Narottam Bansal, NASA Glenn Research Center; Sung Choi, Naval Air Systems Command; Jacques Lamon, CNRS

Monday 8:00 AM
November 2, 2020
Room: Virtual Meeting Room 16
Location: MS&T Virtual

Session Chair: Elizabeth Opila, University of Virginia; Dong Liu, University of Bristol


8:00 AM  
Characterizing Environment-dependent Fracture Mechanisms of SiC-SiC CMCs via Novel Four-point Bend / Hermeticity Test Frame: Clifton Bumgardner1; Frederick Heim1; David Roache1; Xiaodong Li1; 1University of Virginia
    Using a novel four-point bend / hermeticity test frame, we investigate the coupled failure mechanisms and gas-tightness properties of SiC/SiC ceramic matrix composites (CMCs) exposed to high temperature environments up to 1400°C in oxidizing and inert environments. Multiple-perspective, three-dimensional digital image correlation quantified in-situ deformation and strain; the strain maps were refined to track individual crack growth. Internal CMC degradation was characterized via X-ray tomography while the environmental impact on the CMC was characterized via X-ray diffraction and energy-dispersive X-ray spectroscopy. Crack opening displacement was correlated directly with leak rate and acoustic activity, thus identifying critical thresholds for loss of gas tightness, through-thickness matrix cracking, and fiber pullout for CMCs exposed to different harsh environments. This testing identified distinct deformation thresholds leading to ultimate failure, which may be used to govern the safe use of SiC/SiC CMCs in aerospace and nuclear energy applications.

8:20 AM  
Size-dependent Toughness and Strength in Defective SiC and Diamond Nanowires: Zubaer Hossain1; 1University of Delaware
    Defects play a major role in altering the mechanical properties of brittle materials. Yet quantification of toughness and strength degradation in brittle nanowires remains a major challenge due to the associated reduced dimension and difficulty in taking into account the effects of surface and its interaction with a neighboring defect. In this talk, we will present a theoretical and computational understanding of the role of defects of different sizes in governing the strength and toughness behavior of diamond and SiC nanowires of different sizes and shapes. Our results suggest that with decreasing diameter both strength and toughness decrease as a direct consequence of surface softening and geometric confinement of elastic deformation at the defective sites in the nanowire. The defective regime and the surface soften the nanowire and carry the maximum angular deformation at the expense of breaking local symmetry of the atomic structure.

8:40 AM  Invited
Properties of Thermally Grown Borosilicate Glasses and Their Impact on CMC Oxidation and Life Prediction: Kaitlin Detwiler1; Bohuslava McFarland1; Megan Watza1; Elizabeth Opila1; 1University of Virginia
    SiC/BN/SiC composites rely on the BN matrix/fiber interphase for achieving the requisite composite toughness for load-bearing applications, such as turbine engine components. In high temperature oxygen- and water vapor-containing conditions relevant for combustion environments, the BN and SiC phases oxidize to form B2O3 and SiO2, respectively. These oxides in turn combine to form a borosilicate glass. The properties, distribution, and morphology of the borosilicate glasses vary considerably over the range of relevant operating conditions. Viscosity changes by orders of magnitude as a function of composition and temperature. The composition, in turn changes dramatically with temperature and gaseous environment. Finally, the tendency for boria dissolution of SiC leading to rapid SiC fiber degradation also depends on temperature and silica content. Results from laboratory furnace CMC studies in combination with properties available in the literature are reviewed. Implications of the wide range of borosilicate properties on life prediction of SiC/BN/SiC are discussed.

9:20 AM  
Processing and Characterization of Al /Al2O3 Metal Matrix Composites Produced Using Magnetic Field-Assisted Freeze Casting of Porous Ceramic Structures : Said Bakkar1; Jihyung Lee1; Nicholas Ku2; Diana Berman1; Samir Aouadi1; Raymond Brennan2; Marcus Young1; 1University of North Texas; 2U.S. Army Research Laboratory
    In this study, Al/Al2O3 Metal Matrix Composites (MMCs) were produced by metal infiltration of porous ceramic preforms. The porous ceramic preforms were fabricated using the magnetic freeze-casting method, resulting in vertically-aligned porous channels. Preforms were prepared by freezing Al2O3/tert-butyl alcohol (TBA)/polyvinyl alcohol (PVA)/Fe3O4 slurry under an applied vertical magnetic field of 0.3 T. The formed ceramic preforms contained porous channels of 80-100 μm diameter and a total porosity volume fraction of 78.2%, as determined from scanning electron microscopy (SEM) micrographs and ImageJ software. The sintered ceramic preforms were then infiltrated with molten A356 Al-based alloy using the suction pump-assisted infiltration. Mechanical properties of the resulting Al2O3/A356 MMCs were compared to those of the bulk Al2O3, bulk Al-based alloy (A356), and porous Al2O3 preform using micro-indentation testing. The indentation hardness and elastic modulus values of Al2O3/A356 MMCs were found to be in good agreement with experimental and theoretical calculations.

9:40 AM  
Mechanically-robust, Oxidation-resistant, Thermally-cyclable Oxide/Metal Composites for Concentrated Solar Power: Camilla McCormack1; Mario Caccia1; Thuan Nguyen1; Gregory Scofield1; Grigorios Itskos1; Michael Sangid1; Kenneth Sandhage1; 1Purdue University
    A concentrated solar power (CSP) plant transfers heat from focused sunlight to a high-pressure working fluid, such as supercritical carbon dioxide (sCO2), that is then used to drive a turbine to generate electricity. The cost of CSP-derived electricity may be significantly reduced by increasing the temperature of the working fluid entering into the turbine. However, compact stainless-steel-based heat exchangers (HEXs) used to transfer heat to the working fluid have been limited to operational temperatures ≥550oC, owing to significant reductions in the maximum stresses allowed for stainless steels at higher temperatures. In this talk, the use of ceramic/metal composites (cermets), such as Al2O3/Cr cermets, as attractive alternative HEX materials will be discussed. At 750oC, Al2O3/Cr cermets are stiff, possess relatively high failure strengths (>300 MPa), are resistant to oxidation, and are thermally cyclable (owing to similar thermal expansions of Al2O3 and Cr). The fabrication of Al2O3/Cr-based HEXs will also be discussed.