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4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on HfSiOs by Materials Project

HfOsSi crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Hf is bonded in a 11-coordinate geometry to six equivalent Os and five Si atoms. There are two shorter (2.92 Å) and four longer (3.04 Å) Hf–Os bond lengths. There are four shorter (2.73 Å) and one longer (2.75 Å) Hf–Si bond lengths. Os is bonded in a 12-coordinate geometry to six equivalent Hf and four Si atoms. There are two shorter (2.48 Å) and two longer (2.55 Å) Os–Si bond lengths. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to six equivalent Hf and three equivalent Os atoms. In the second Si site, Si is bonded in a 9-coordinate geometry to three equivalent Hf and six equivalent Os atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HfSiOs by Materials Project

HfOsSi crystallizes in the orthorhombic Ima2 space group. The structure is three-dimensional. there are three inequivalent Hf sites. In the first Hf site, Hf is bonded in a 11-coordinate geometry to six Os and five Si atoms. There are a spread of Hf–Os bond distances ranging from 2.85–2.96 Å. There are a spread of Hf–Si bond distances ranging from 2.71–2.95 Å. In the second Hf site, Hf is bonded in a 5-coordinate geometry to four Os and five Si atoms. There are two shorter (2.90 Å) and two longer (3.14 Å) Hf–Os bond lengths. There are a spread of Hf–Si bond distances ranging from 2.71–2.73 Å. In the third Hf site, Hf is bonded in a 9-coordinate geometry to six Os and five Si atoms. There are a spread of Hf–Os bond distances ranging from 2.88–3.17 Å. There are a spread of Hf–Si bond distances ranging from 2.71–2.76 Å. There are two inequivalent Os sites. In the first Os site, Os is bonded in a 12-coordinate geometry to five Hf, one Os, and four Si atoms. The Os–Os bond length is 2.87 Å. There are a spread of Os–Si bond distances ranging from 2.47–2.55 Å. In the second Os site, Os is bonded in a 12-coordinate geometry to six Hf, two equivalent Os, and four Si atoms. There are two shorter (2.54 Å) and two longer (2.56 Å) Os–Si bond lengths. There are two inequivalent Si sites. In the first Si site, Si is bonded in a 9-coordinate geometry to six Hf and three Os atoms. In the second Si site, Si is bonded in a 9-coordinate geometry to three Hf and six Os atoms.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

High-Temperature Slurry Environmental Barrier Coating With Graded HfO 2 -HfSiO 4 Topcoat

Environmental barrier coatings (EBCs) have enabled the use of silicon carbide (SiC)-based ceramic matrix composites (CMCs) in gas turbine engines by protecting the underlying CMC from corrosive combustion species. Current-generation EBCs consist of a rare earth silicate topcoat and a silicon bond coat. The relatively low melting point of the silicon bond coat (1414°C) limits the upper use temperature of these coatings. To protect SiC-based CMCs at temperatures beyond that achievable by the current state-of-the-art, an oxide-based bond coat capable of withstanding temperatures of up to 1482°C has been developed at NASA Glenn Research Center. Hafnia (HfO2) is a promising EBC topcoat material due to its stability in high-temperature steam; however, its coefficient of thermal expansion (CTE) is highly anisotropic and much larger than that of SiC. In this study, a graded HfO2-HfSiO4 topcoat was deposited via a slurry process on the NASA-developed oxide-based bond coat. The oxidation resistance of this EBC system was evaluated at 1482°C in a steam cycling environment. The durability and stability of this slurry-deposited HfO2-HfSiO4 topcoat was compared to that of HfO2 deposited by plasma spray physical vapor deposition (PS-PVD).

EBC↗
DOE OSTI2024

Holistic comparison of environmental barrier coating material candidates through design of a figure of merit

The first figure of merit for environmental barrier coating (EBC) materials was designed through a ranking system for material properties pertaining to established EBC failure modes in service. Seven past, present, and novel EBC candidate materials were used in the figure of merit design: SiO 2 , Ba 0.75 Sr 0.25 Al 2 Si 2 O 8 (BSAS), HfSiO 4 , Yb 2 Si 2 O 7 , Yb 2 SiO 5 , Yb 2 O 3 , and YbPO 4 . Utilizing compiled data from the literature, the presented figure of merit verified Yb 2 Si 2 O 7 as the state-of-the-art candidate with optimal EBC properties and inferred that YbPO 4 should be considered as a potentially viable EBC material candidate. Further, the figure of merit allows for a holistic comparison of EBC candidates and informs experimental and computational search efforts for next-generation complex EBCs. Clear knowledge gaps found through this work include CaO–MgO–Al 2 O 3 –SiO 2 (CMAS)-resistant coatings, EBC lifetimes before delamination, and oxidant diffusion rates in relevant EBC microstructures. It was shown that while some materials show promise for solving a single key failure mode for EBCs (i.e., CMAS reactivity), a community-wide goal should be placed on materials development to achieve acceptable resistance against all major failure modes, which are interconnected. Novel compositionally complex EBC materials, in addition to layered EBC architectures, show promise for the optimization of material properties for long-lifetime EBCs in combustion environments.

36 MATERIALS SCIENCE↗