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At least 19 records

All sources NASA NTRS DOE OSTI

NASA NTRS2018

Microscale Fracture Testing of HfO2-Si Environmental Barrier Coatings

Environmental barrier coatings (EBCs) play a vital role in protecting advanced turbine components constructed from ceramic matrix composites. EBC performance is evaluated based on many factors such as mechanical and thermal properties and chemical stability. This study focuses on the mechanical properties of individual phases within a HfO2-Si EBC through the combined use of chevron-notched microcantilevers and finite element modeling. The Si- and HfO2-rich phases were found to have fracture toughness K(sub IC) values of 1.36+/-0.07 MPa·m1/2 and 1.99+/-0.36 MPa·m1/2, respectively. Despite irregular notch geometry, calculated K(sub IC) values agreed reasonably with literature values of monolithic samples for the respective phases. The relatively large scatter in the HfO2-rich samples is attributed to heterogeneity in fracture feature size and distribution of the HfO2 and HfSiO4 phases. Comparisons with bulk single-edge V-notched beams suggest bulk behavior is dictated by the fracture behavior of the Sirich phase with no contribution from the HfO2-rich phase.

Robertson, Andrew L.↗

NASA NTRS2004

Thermal Conductivity and Water Vapor Stability of Ceramic HfO2-Based Coating Materials

HfO2-Y2O3 and La2Zr2O7 are candidate thermal/environmental barrier coating materials for gas turbine ceramic matrix composite (CMC) combustor liner applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature phase stability of plasma-sprayed coatings and/or hot-pressed HfO2-5mol%Y2O3, HfO2-15mol%Y2O3 and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasma-sprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC Hexoloy or CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications will also be discussed.

Zhu, Dong-Ming↗

NASA NTRS2014

Development and Performance Evaluations of HfO2-Si and Rare Earth-Si Based Environmental Barrier Bond Coat Systems for SiC/SiC Ceramic Matrix Composites

Ceramic environmental barrier coatings (EBC) and SiCSiC ceramic matrix composites (CMCs) will play a crucial role in future aircraft propulsion systems because of their ability to significantly increase engine operating temperatures, improve component durability, reduce engine weight and cooling requirements. Advanced EBC systems for SiCSiC CMC turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant material development challenges for the high temperature CMC components is to develop prime-reliant, high strength and high temperature capable environmental barrier coating bond coat systems, since the current silicon bond coat cannot meet the advanced EBC-CMC temperature and stability requirements. In this paper, advanced NASA HfO2-Si based EBC bond coat systems for SiCSiC CMC combustor and turbine airfoil applications are investigated. The coating design approach and stability requirements are specifically emphasized, with the development and implementation focusing on Plasma Sprayed (PS) and Electron Beam-Physic Vapor Deposited (EB-PVD) coating systems and the composition optimizations. High temperature properties of the HfO2-Si based bond coat systems, including the strength, fracture toughness, creep resistance, and oxidation resistance were evaluated in the temperature range of 1200 to 1500 C. Thermal gradient heat flux low cycle fatigue and furnace cyclic oxidation durability tests were also performed at temperatures up to 1500 C. The coating strength improvements, degradation and failure modes of the environmental barrier coating bond coat systems on SiCSiC CMCs tested in simulated stress-environment interactions are briefly discussed and supported by modeling. The performance enhancements of the HfO2-Si bond coat systems with rare earth element dopants and rare earth-silicon based bond coats are also highlighted. The advanced bond coat systems, when integrated with advanced EBC top coats, showed promise to achieve 1500 C temperature capability, helping enable next generation turbine engines with significantly improved engine component temperature capability and long-term durability.

HfO2-Si bond coat↗

NASA NTRS2003

Thermal Conductivity and Stability of HfO2-Y2O3 and La2Zr2O7 Evaluated for 1650 Deg C Thermal/Environmental Barrier Coating Applications

HfO2-Y2O3 and La2Zr2O7 are candidate thermal and environmental barrier coating (T/EBC) materials for gas turbine ceramic matrix composite (CMC) combustor applications because of their relatively low thermal conductivity and high temperature capability. In this paper, thermal conductivity and high temperature stability of hot-pressed and plasma sprayed specimens with representative partially-stabilized and fully-cubic HfO2-Y2O3 compositions and La2Zr2O7 were evaluated at temperatures up to 1700 C using a steady-state laser heat-flux technique. Sintering behavior of the plasmasprayed coatings was determined by monitoring the thermal conductivity increases during a 20-hour test period at various temperatures. Durability and failure mechanisms of the HfO2-Y2O3 and La2Zr2O7 coatings on mullite/SiC hexoloy or SiC/SiC CMC substrates were investigated at 1650 C under thermal gradient cyclic conditions. Coating design and testing issues for the 1650 C thermal/environmental barrier coating applications are also discussed.

Zhu, Dong-Ming↗

DOE OSTI2024

Phase transitions in HfO2 probed by first-principles computations

Ever since ferroelectricity was discovered in HfO2, the question of its origin remains controversial. Here, we probe this question using a combination of Landau theory of phase transitions and first-principles computations. In such an approach, the energy landscape associated with the phase transition between cubic and different experimentally demonstrated phases of HfO2 (tetragonal, monoclinic, orthorhombic Pbca, orthorhombic Pnma, and orthorhombic Pca21) is explored using density functional theory calculations. Computations revealed that stabilization of all but orthorhombic Pbca phase is driven by a single unstable zone-boundary antipolar mode X2−. When coupled with zone-center modes (Γ1+ and Γ3+), it stabilizes the tetragonal phase. Coupling with four additional modes (Γ5+, X3−, X5−, X5+) results in the monoclinic phase, which is the ground state of the material. If, however, Γ5+ mode is replaced with Γ4− mode, orthorhombic polar phase Pca21 is stabilized. The application of this framework to examine the effect of electric field on the ferroelectric phase of hafnia reveals that the field of 5 MV/cm is capable of stabilizing ferroelectric phase over the monoclinic one at 0 K.

Physics↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Baddeleyite-like structured and crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Hf4+ is bonded to seven O2- atoms to form a mixture of distorted edge and corner-sharing HfO7 pentagonal bipyramids. There are a spread of Hf–O bond distances ranging from 2.05–2.22 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Hf4+ atoms to form a mixture of edge and corner-sharing OHf4 tetrahedra. In the second O2- site, O2- is bonded in a trigonal planar geometry to three equivalent Hf4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Baddeleyite structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Hf4+ is bonded to seven O2- atoms to form a mixture of distorted corner and edge-sharing HfO7 pentagonal bipyramids. There are a spread of Hf–O bond distances ranging from 2.05–2.26 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Hf4+ atoms. In the second O2- site, O2- is bonded to four equivalent Hf4+ atoms to form a mixture of distorted corner and edge-sharing OHf4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Hf4+ is bonded in a body-centered cubic geometry to eight equivalent O2- atoms. All Hf–O bond lengths are 2.20 Å. O2- is bonded to four equivalent Hf4+ atoms to form a mixture of edge and corner-sharing OHf4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Baddeleyite-like structured and crystallizes in the orthorhombic Pca2_1 space group. The structure is three-dimensional. Hf4+ is bonded to seven O2- atoms to form a mixture of distorted edge and corner-sharing HfO7 pentagonal bipyramids. There are a spread of Hf–O bond distances ranging from 2.04–2.25 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to three equivalent Hf4+ atoms. In the second O2- site, O2- is bonded to four equivalent Hf4+ atoms to form a mixture of edge and corner-sharing OHf4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Hf4+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of Hf–O bond distances ranging from 2.14–2.59 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Hf4+ atoms to form a mixture of edge and corner-sharing OHf4 tetrahedra. In the second O2- site, O2- is bonded in a 3-coordinate geometry to five equivalent Hf4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Baddeleyite-like structured and crystallizes in the orthorhombic Pbca space group. The structure is three-dimensional. Hf4+ is bonded to seven O2- atoms to form a mixture of distorted corner and edge-sharing HfO7 pentagonal bipyramids. There are a spread of Hf–O bond distances ranging from 2.05–2.23 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Hf4+ atoms. In the second O2- site, O2- is bonded to four equivalent Hf4+ atoms to form a mixture of corner and edge-sharing OHf4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Hydrophilite-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. there are two inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 50–53°. There are a spread of Hf–O bond distances ranging from 2.09–2.11 Å. In the second Hf4+ site, Hf4+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 50–53°. There are a spread of Hf–O bond distances ranging from 2.04–2.16 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three equivalent Hf4+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Hf4+ atoms. In the third O2- site, O2- is bonded in a trigonal planar geometry to three Hf4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Hf4+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing HfO6 octahedra. The corner-sharing octahedral tilt angles are 50°. All Hf–O bond lengths are 2.10 Å. O2- is bonded in a distorted trigonal planar geometry to three equivalent Hf4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 crystallizes in the tetragonal P4_2/nmc space group. The structure is three-dimensional. Hf4+ is bonded in a distorted body-centered cubic geometry to eight equivalent O2- atoms. There are four shorter (2.07 Å) and four longer (2.40 Å) Hf–O bond lengths. O2- is bonded to four equivalent Hf4+ atoms to form a mixture of distorted edge and corner-sharing OHf4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on HfO2 by Materials Project

HfO2 is Baddeleyite-like structured and crystallizes in the orthorhombic P2_12_12 space group. The structure is three-dimensional. Hf4+ is bonded to seven O2- atoms to form a mixture of distorted corner, edge, and face-sharing HfO7 pentagonal bipyramids. There are a spread of Hf–O bond distances ranging from 2.01–2.28 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to three equivalent Hf4+ atoms. In the second O2- site, O2- is bonded to four equivalent Hf4+ atoms to form a mixture of distorted corner and edge-sharing OHf4 trigonal pyramids. In the third O2- site, O2- is bonded to four equivalent Hf4+ atoms to form a mixture of corner and edge-sharing OHf4 tetrahedra.

36 MATERIALS SCIENCE↗

NASA NTRS1990

Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters

An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

Zukic, Muamer↗

NASA NTRS2016

Development and Property Evaluation of Selected HfO2-Silicon and Rare Earth-Silicon Based Bond Coats and Environmental Barrier Coating Systems for SiC/SiC Ceramic Matrix Composites

Ceramic environmental barrier coatings (EBC) and SiC/SiC ceramic matrix composites (CMCs) will play a crucial role in future aircraft propulsion systems because of their ability to significantly increase engine operating temperatures, improve component durability, reduce engine weight and cooling requirements. Advanced EBC systems for SiC/SiC CMC turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant material development challenges for the high temperature CMC components is to develop prime-reliant, high strength and high temperature capable environmental barrier coating bond coat systems, since the current silicon bond coat cannot meet the advanced EBC-CMC temperature and stability requirements. In this paper, advanced NASA HfO2-Si and rare earth Si based EBC bond coat EBC systems for SiC/SiC CMC combustor and turbine airfoil applications are investigated. High temperature properties of the advanced EBC systems, including the strength, fracture toughness, creep and oxidation resistance have been studied and summarized. The advanced NASA EBC systems showed some promise to achieve 1500C temperature capability, helping enable next generation turbine engines with significantly improved engine component temperature capability and durability.

Oxidation and cyclic durability↗

NASA NTRS2017

Environmental Stability and Oxidation Behavior of HfO2-Si and YbGd(O) Based Environmental Barrier Coating Systems for SiCSiC Ceramic Matrix Composites

Ceramic Matrix Composites↗