Formulations for engineered ceramic matrix composites for high temperature applications
An engineered ceramic matrix is provided to blunt and self-heal matrix cracks to reduce oxygen ingress into a fiber reinforced composite.
36 MATERIALS SCIENCE↗
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Phase Transformation Pathway of DyPO4 to 21.5 GPa
Interest in the deformation behavior and phase transformations of rare earth orthophosphates (REPO4s) spans several fields of science—from geological impact analysis to ceramic matrix composite engineering. In this study, the phase behavior of polycrystalline, xenotime DyPO4 is studied up to 21.5(16) GPa at ambient temperature using in situ diamond anvil cell synchrotron X-ray diffraction. This experiment reveals a large xenotime–monazite phase coexistence pressure range of 7.6(15) GPa and evidence for the onset of a post-monazite transformation at 13.9(10) GPa to scheelite. The identification of scheelite as the post-monazite phase of DyPO4, though not definitive, is consistent with REPO4 phase transformation pathways reported in both the experimental and the computational literature.
Sharma, Jai (ORCID:0000000339034534)↗
Water Vapor Resistant SiC/SiC Composite for Hydrogen-Based Turbines (Final Scientific Technical Report)
New material innovations are needed for the extreme environments of next generation, hydrogen-fueled turbine engines. Ceramic matrix composites (CMCs) offer high-temperature capability but are susceptible to degradation in high-temperature water vapor. Pratt & Whitney’s (P&W) baseline silicon carbide (SiC)/SiC CMC was initially applied to design a component in a hydrogen-fueled engine, verifying the existence of a design space and extracting boundary conditions to inform testing parameters. Several material innovations, including two fibers, interface coatings (IFC), and self-healing matrices (SHM), were investigated to improve high-temperature performance in water vapor. A boron-doped pyrocarbon (B-PyC) IFC and a SHM matrix with layers of zirconium nitride (ZrN) or zirconium diboride (ZrB 2 ) were developed to fabricate minicomposites with either standard Hi-Nicalon™ Type S (HNS) fibers or new Tyranno® SA4 fibers (SA4). The B-PyC IFC is functional but lacks in providing improved durability. A matrix consisting of thick layers of SiC and thin layers of ZrB 2 shows promise as a SHM that can effectively seal matrix cracks in this extreme environment. Minicomposites with HNS fibers generally outperform those with SA4 fibers.
08 HYDROGEN↗
A novel fiber-fretting test for tribological characterization of the fiber/matrix interface
Ceramic matrix composites exhibit excellent high temperature properties and are candidate materials for structural applications from jet engines to nuclear fuel cladding. The strength and deformation behavior of these composites are intrinsically tied to the properties of the fiber/matrix interface. This research introduces a novel technique to evaluate the fundamental friction and wear characteristics of these interfaces. A case study on SiC f /PyC/SiC m composites applies in situ fiber fretting to investigate the kinetic friction coefficient and cyclic wear characteristics of the interphase. The experimental methodology is presented in explicit detail to encourage other researchers to explore the capabilities of this technique. Additionally, testing was carried out as a function of fiber roughness, PyC thickness (≈10, 500, 1200 nm), cycle count (10, 100, 1000), and frequency (1, 5, and 10 Hz). The friction coefficient and wear behavior changed with cycle length due to a transition from adhesive to abrasive mechanisms. SEM fractography provided insights to tribological evolution from adhesive sliding to three-body abrasive wear. The structural disorder at the tribo-surface relating to graphitic content and dangling bond density was investigated using Raman spectroscopy. Properties are contextualized with comparison to uniaxial tensile behavior of the parent composite.
36 MATERIALS SCIENCE↗
Engineered Water for Improved Oil Recovery from Fractured Reservoirs (Final Scientific/Technical Report)
The goal of this proposal is to field test the novel technology of engineered water (modifying ionic composition and/or adding surfactants or nanoparticles) injection to improve oil recovery from the carbonate matrix in fractured reservoirs. Carbonate reservoirs tend to be oil-wet/mixed-wet due to positively charged carbonate mineral surfaces and negatively charged acidic/asphaltic components in the oil. Many carbonate reservoirs are also highly fractured. Water injection does not work efficiently in fractured oil-wet reservoirs because water does not imbibe into the matrix. The water composition can be engineered with ionic modification, surfactants and nanoparticles which can change the wettability of carbonate rocks towards more water-wet conditions which can imbibe water into the matrix and push the oil into the fractures. The engineered water can also lower interfacial tension and minimize capillary forces so that gravity can push the oil up and out of the matrix. Wettability alteration also increases water relative permeability which can also improve oil recovery in non-fractured carbonate reservoirs. This technology, if successful, can be a game changer for West Texas carbonates.
02 PETROLEUM↗
Optimization of matrix viscosity improves polypropylene fiber dispersion and properties of engineered cementitious composites
Engineered cementitious composites (ECC) is a durable cementitious material with high tensile ductility and strain-hardening characteristics. Although considered as a cost-effective fiber for ECC, polypropylene (PP) fiber is reportedly difficult to disperse in mortar matrix due to its high aspect ratio and hydrophobicity. In this study, the matrix viscosity of a low-carbon ECC based on limestone calcined clay cement was tailored as a variable to improve PP fiber dispersion under a pre-determined mixing protocol. The effect of matrix viscosity on the composite fresh and hardened properties was investigated experimentally. Results suggested an optimal range of matrix viscosity (10.3–11.5 Pa . s) favors the composite tensile strength and strain capacity at 28 days. At the optimal state with a 0.1 % viscosity modifying admixture (VMA)-to-binder mass ratio, PP-ECC achieved 7.0 % tensile strain capacity and 3.5 MPa ultimate tensile strength. When matrix viscosity falls outside the desired range, both ultimate tensile strength and strain capacity were diminished. By tailoring the VMA dosage, the matrix viscosity can be adjusted for desired fiber dispersion, workability, and mechanical properties. Finally, the findings of this study provide a technical reference for the practical design and application of PP-ECC.
36 MATERIALS SCIENCE↗
Enhanced defect annihilation capability of the graphene/copper interface: An in situ study
It is well known that energetic heavy ion irradiations can often induce defects and ultimately lead to material degradations. Interfaces, such as high-angle grain boundaries (HAGBs), are generally used as defect sinks for alleviating the irradiation damage. However, HAGBs are often unstable during radiation. Here we investigate the interfacial irradiation responses of the graphene (Gr)/Cu composites by using in situ Kr ++ ions irradiation under transmission electron microscopy. The results revealed that the Gr/Cu interface exhibits higher defect annihilation capability compared to the HAGBs in Cu. Moreover, the atomistic simulations suggested a slightly higher and larger range of stress field for the Gr/Cu interface, which contributes to the enhanced defects absorption capability. The present findings are essential to understand and design a new class of carbon/metal composites with superior irradiation tolerance.
36 MATERIALS SCIENCE↗
Predicting EBC Temperature Limits for Industrial Gas Turbines
Higher turbine inlet temperatures may require the use of ceramic matrix composites (CMC) such as SiC/SIC, which require environmental barrier coatings (EBCs) to protect them against the detrimental effect of water vapor. Here, the goal of this project is to determine the maximum bond coating temperature for EBCs for land-based turbines, where the minimum coating lifetime is 25,000 h. If the temperature exceeds the 1414°C melting point of the Si bond coating, then coatings without a bond coating also need to be evaluated. Thus, current Yb 2 Si 2 O 7 EBCs with a Si bond coating and next-generation EBCs without a Si bond coating are being evaluated in laboratory testing using 1-h cycles in air+90%H 2 O. For this initial work, coatings were deposited on CVD SiC coupons. Reaction kinetics at 1250°, 1300° and 1350°C have been evaluated by measuring the thickness of the thermally grown silica scale after 100–500 h exposures. For comparison, scale growth rates for uncoated SiC and Si specimens in dry and wet environments were included as minimum and maximum values, respectively. Based on a critical scale thickness failure criteria, estimated maximum temperatures were calculated for both EBC systems using this initial data.
42 ENGINEERING↗
A mean field homogenization model for the mechanical response of ceramic matrix composites
SiC/SiC composites offer exceptional mechanical stability at high temperatures and under irradiation. These ceramic matrix composites are therefore strong candidate materials for future nuclear energy applications. Their mechanical response, which exhibits pseudo-plasticity, is mediated by matrix cracking, fiber debonding, and fiber pull-out due to slip. Here, this study introduces a mechanistic model for the behavior of unidirectionally reinforced SiC/SiC composites. Specifically a mean field homogenization approach is proposed to account for all deformation and degradation modes during mechanical deformation. The homogenization scheme relies on a Mori Tanaka method that is extended to consider the effects of the coating’s elasto-plastic response on the development of micromechanical fields. Further, the model proposed introduces a method to effectively account for the role of localized damage (i.e., cracks) on mechanical fields within both the fiber and the matrix. Upon validating the model against experimental data, the roles of interface sliding, coating dimensions and intrinsic elastic response, as well as of microstructure (e.g. porosity, fiber volume fraction) are discussed.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
High pressure effects on EBC systems in high temperature environments
Environmental barrier coatings (EBCs) are designed to protect SiCfiber/SiCmatrix ceramic matrix composites (CMCs) in turbine engines by mitigating wear in high-temperature water vapor environments. The failure of EBCs is frequently attributed to the accelerated oxidation of the silicon bond coating layer when exposed to high-temperature steam, leading to the formation of a thickened thermally grown oxide (TGO). TGO growth increases interfacial stress, weakens adhesion, and results in coating spallation. Understanding the impact of high-temperature oxidation of EBC systems is essential for developing accurate lifespan models for turbine components, although pressurized oxidation testing is extremely sparse in the open literature. In this work, oxidation tests were performed on rare earth silicate EBCs coated onto SiC substrates under increased pressure conditions. The coated specimens were tested at 1100°C, 1200°C, and 1300°C at both 1 atm and 10 atm total pressure in steam environments. Subsequent characterization focused on the microstructural evolution of the EBC/Si/SiC system. The experimental findings indicated that TGO behavior is dependent on high-pressure conditions, with elevated pressure leading to an increase in oxide scale thickness and modifications in its morphology.
Ardrey, Kristyn [ORNL] (ORCID:0000000184407796)↗
Melting temperature, emissivity, and thermal conductivity of rare-earth silicates for thermal and environmental barrier coatings
In recent years, rare-earth silicates have become the industry standard for coating state-of-the-art SiC ceramic matrix composite (CMC) gas turbine engine components, due to their low volatility, high melting point, and thermal shock resistance. Current research is focused on designing rare-earth silicate based thermal-environmental barrier coatings (T/EBCs) with improved resistance to CMAS (CaO-MgO-Al 2 O 3 -SiO 2 ), steam, and crack formation, while maintaining high temperature performance and stability. Here, in this work we compare the high temperature performance of a variety of single and multi-component rare-earth mono- and disilicates (MS, DS) and rare earth apatites by measuring their melting points and spectrally averaged visible emissivities using laser heating and radiation pyrometry. We also report room temperature thermal conductivity measured by time-domain thermoreflectance (TDTR).
Environmental barrier coatings↗
Corrosion of Al 2 O 3 /Cr and Ti 2 O 3 /Cr composites in flowing air and CO 2 at 750°C
Hot-pressed Al 2 O 3 /Cr and Ti 2 O 3 /Cr composites were exposed to synthetic air or CO 2 at 750 °C. The Al 2 O 3 /Cr composites formed external Cr 2 O 3 scales, and exhibited slow parabolic oxidation kinetics, in both gases. The Cr 2 O 3 scales formed in CO 2 possessed finer grains, and thickened at a faster rate, than Cr 2 O 3 scales formed in air. The Ti 2 O 3 /Cr composites formed thick external TiO 2 scales with internal oxidation zones that also contained Cr 2 O 3 scales on subsurface Cr grains. After 20 h at 750 °C, the Ti 2 O 3 /Cr composites exhibited parabolic oxidation kinetics in both gases, although the oxidation rates were significantly higher than for the Al 2 O 3 /Cr composites.
36 MATERIALS SCIENCE↗
An IIPG-based finite element framework in MOOSE for modeling fiber reinforced composite failure governed by extrinsic cohesive laws
Fiber reinforced composites (FRC) are widely applied to many important engineering structures such as silicon carbide ceramic matrix composite (SiC CMC) of nuclear fuel claddings. Many material and structure failures are initiated at the interface between two distinctive materials, such as the debonding of interfaces of matrix/fiber of composites or bulk matrix/inclusion in metals at micro-scales. Accurate and robust modeling of these interface failures is critical to the development of novel material and structure with improved functionality. This paper presents a discontinuous Galerkin (DG) finite element method based on the Incomplete Interior Penalty scheme and its implementation in MOOSE for modeling material interface behaviors. The proposed method naturally accommodates important extrinsic cohesive zone material models and is capable of modeling the failures of material interfaces across which material properties are highly distinctive. We demonstrate a good performance of the proposed method using single fiber and multiple fiber debonding problems.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
On the interactions between molten aluminum and high entropy alloy particles during aluminum matrix composite processing
The feasibility of adding AlCrTiV high entropy alloy (HEA) particles to molten aluminum to make metal matrix composites was studied. Equiatomic AlCrTiV HEA particles, produced by a solid state reduction process, were dispersed into pure aluminum and 7075 alloy (Al-5.8Zn-2.3Mg-1.4Cu, all weight %) melt and by a ultrasonic dispenser. It was found that the AlCrTiV particles reacted with molten aluminum, leading to the formation of Al 45 (Cr,V) 7 and Al 3 Ti intermetallic phases in the aluminum matrix composites. Although the AlCrTiV HEA particles did not survive in molten aluminum during composite processing, the final composite materials showed significantly improved mechanical properties, due to grain refinement and dispersion strengthening. Finally, the research suggests that the interactions between matrix aluminum alloys and the particles are key in controlling the final microstructure and properties of the composites.
36 MATERIALS SCIENCE↗
Advanced Materials for CSP Molten Salt Storage
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36 MATERIALS SCIENCE↗
Additive manufacturing enabled synergetic strengthening of bimodal reinforcing particles for aluminum matrix composites
An additive manufactured TiB 2 /Al-Cu-Mg-Ni composite with a minor amount of Sc was fabricated by laser powder bed fusion (LPBF). The composite shows a yield strength of ~370 MPa, almost doubling the strength of its wrought matrix counterpart, and an elongation of ~7 %. The superior mechanical properties are attributed to a unique micro-nano hierarchical microstructure, consisting of nanoscale and microscale TiB 2 particles dispersed in a matrix of fine aluminum grains (3 µm) together with intragranular intermetallic nanoparticles and nano-cellular networks (cell size 30 nm). The formation of the TiB 2 nanoparticles is the consequence of partial dissolution of the TiB 2 particulates and the enrichment of Sc in the newly formed nanoparticles. Remarkable strengthening effects are achieved by the bimodal TiB 2 particles, intermetallic nanoparticles and intragranular nano-cellular networks. Finally, this study provides new insights into the role of additive manufacturing in tailoring the microstructure of particulate reinforced metal matrix composites (MMCs) with advanced properties.
36 MATERIALS SCIENCE↗