Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Cr”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Cr(PO4)2 by Materials Project

Cr(PO4)2 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of two Cr(PO4)2 sheets oriented in the (0, 0, 1) direction. Cr6+ is bonded to six O2- atoms to form distorted CrO6 octahedra that share corners with five PO4 tetrahedra. There are a spread of Cr–O bond distances ranging from 1.59–2.15 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with three equivalent CrO6 octahedra and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 27–55°. There are a spread of P–O bond distances ranging from 1.52–1.62 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CrO6 octahedra and a cornercorner with one PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 31–48°. There are a spread of P–O bond distances ranging from 1.52–1.62 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Cr6+ and one P5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Cr6+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Cr6+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a single-bond geometry to one Cr6+ atom. In the sixth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cr6+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the eighth O2- site, O2- is bonded in a bent 120 degrees geometry to one Cr6+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr(PO3)5 by Materials Project

Cr(PO3)5 crystallizes in the monoclinic Pc space group. The structure is two-dimensional and consists of one Cr(PO3)5 sheet oriented in the (0, 1, 0) direction. Cr5+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Cr–O bond distances ranging from 1.98–2.07 Å. There are five inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CrO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 42–43°. There is two shorter (1.50 Å) and two longer (1.61 Å) P–O bond length. In the third P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.60 Å. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CrO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 47–48°. There is two shorter (1.51 Å) and two longer (1.62 Å) P–O bond length. In the fifth P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CrO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 40–43°. There is two shorter (1.50 Å) and two longer (1.61 Å) P–O bond length. There are fifteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cr5+ and one P5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cr5+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the seventh O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the ninth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cr5+ and one P5+ atom. In the tenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cr5+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cr5+ and one P5+ atom. In the twelfth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two P5+ atoms. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cr5+ and one P5+ atom. In the fourteenth O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the fifteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr(PO3)5 by Materials Project

Cr(PO3)5 crystallizes in the monoclinic P2_1/m space group. The structure is two-dimensional and consists of one Cr(PO3)5 sheet oriented in the (0, 0, 1) direction. Cr5+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six PO4 tetrahedra. There are a spread of Cr–O bond distances ranging from 1.91–1.99 Å. There are three inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one CrO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedral tilt angles are 41°. There are a spread of P–O bond distances ranging from 1.47–1.64 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with two equivalent CrO6 octahedra and corners with two PO4 tetrahedra. The corner-sharing octahedra tilt angles range from 47–49°. There are a spread of P–O bond distances ranging from 1.51–1.60 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There is two shorter (1.51 Å) and two longer (1.61 Å) P–O bond length. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cr5+ and one P5+ atom. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two P5+ atoms. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Cr5+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two P5+ atoms. In the sixth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent P5+ atoms. In the seventh O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to one Cr5+ and one P5+ atom. In the ninth O2- site, O2- is bonded in a single-bond geometry to one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr(GaS2)2 by Materials Project

Cr(GaS2)2 crystallizes in the monoclinic Cm space group. The structure is two-dimensional and consists of one Cr(GaS2)2 sheet oriented in the (0, 0, 1) direction. Cr2+ is bonded to six S2- atoms to form CrS6 octahedra that share corners with six GaS4 tetrahedra and edges with six equivalent CrS6 octahedra. There are four shorter (2.47 Å) and two longer (2.49 Å) Cr–S bond lengths. There are two inequivalent Ga3+ sites. In the first Ga3+ site, Ga3+ is bonded to four S2- atoms to form GaS4 tetrahedra that share corners with three equivalent CrS6 octahedra and corners with six equivalent GaS4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–60°. There are a spread of Ga–S bond distances ranging from 2.29–2.36 Å. In the second Ga3+ site, Ga3+ is bonded to four S2- atoms to form GaS4 tetrahedra that share corners with three equivalent CrS6 octahedra and corners with six equivalent GaS4 tetrahedra. The corner-sharing octahedra tilt angles range from 59–60°. There are a spread of Ga–S bond distances ranging from 2.29–2.36 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to three equivalent Cr2+ and one Ga3+ atom to form a mixture of distorted edge and corner-sharing SCr3Ga trigonal pyramids. In the second S2- site, S2- is bonded to three equivalent Cr2+ and one Ga3+ atom to form a mixture of distorted edge and corner-sharing SCr3Ga trigonal pyramids. In the third S2- site, S2- is bonded in a trigonal non-coplanar geometry to three equivalent Ga3+ atoms. In the fourth S2- site, S2- is bonded in a trigonal non-coplanar geometry to three equivalent Ga3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr(NO2)2 by Materials Project

CrN2O5CrN2O3 crystallizes in the monoclinic Pm space group. The structure is one-dimensional and consists of one CrN2O3 ribbon oriented in the (0, 1, 0) direction and one CrN2O5 ribbon oriented in the (0, 1, 0) direction. In the CrN2O3 ribbon, Cr6+ is bonded in a tetrahedral geometry to one N1+ and three O2- atoms. The Cr–N bond length is 1.55 Å. There is one shorter (1.61 Å) and two longer (1.98 Å) Cr–O bond length. There are two inequivalent N1+ sites. In the first N1+ site, N1+ is bonded in a water-like geometry to two equivalent O2- atoms. Both N–O bond lengths are 1.28 Å. In the second N1+ site, N1+ is bonded in a single-bond geometry to one Cr6+ atom. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to one Cr6+ and one N1+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one Cr6+ atom. In the CrN2O5 ribbon, Cr6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Cr–O bond distances ranging from 1.60–1.92 Å. There are two inequivalent N1+ sites. In the first N1+ site, N1+ is bonded in a single-bond geometry to one O2- atom. The N–O bond length is 1.22 Å. In the second N1+ site, N1+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms. There is one shorter (1.15 Å) and two longer (2.02 Å) N–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Cr6+ and one N1+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to one Cr6+ and one N1+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one Cr6+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one N1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr(NO3)5 by Materials Project

Cr(NO3)5 is alpha Selenium structured and crystallizes in the trigonal P3_221 space group. The structure is zero-dimensional and consists of three Cr(NO3)5 clusters. Cr5+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Cr–O bond distances ranging from 2.04–2.07 Å. There are three inequivalent N5+ sites. In the first N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is two shorter (1.24 Å) and one longer (1.31 Å) N–O bond length. In the second N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of N–O bond distances ranging from 1.24–1.30 Å. In the third N5+ site, N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.21 Å) and two longer (1.31 Å) N–O bond length. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the second O2- site, O2- is bonded in an L-shaped geometry to one Cr5+ and one N5+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the fourth O2- site, O2- is bonded in a bent 120 degrees geometry to one Cr5+ and one N5+ atom. In the fifth O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the sixth O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the seventh O2- site, O2- is bonded in a bent 120 degrees geometry to one Cr5+ and one N5+ atom. In the eighth O2- site, O2- is bonded in a single-bond geometry to one N5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr(PO3)2 by Materials Project

Cr(PO3)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Cr2+ sites. In the first Cr2+ site, Cr2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Cr–O bond distances ranging from 2.08–2.13 Å. In the second Cr2+ site, Cr2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Cr–O bond distances ranging from 2.07–2.43 Å. There are four inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.63 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.50–1.61 Å. In the third P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.47–1.63 Å. In the fourth P5+ site, P5+ is bonded to four O2- atoms to form corner-sharing PO4 tetrahedra. There are a spread of P–O bond distances ranging from 1.49–1.62 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Cr2+ and one P5+ atom. In the second O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Cr2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cr2+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to two Cr2+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms. In the eighth O2- site, O2- is bonded in a bent 120 degrees geometry to two P5+ atoms. In the ninth O2- site, O2- is bonded in a 2-coordinate geometry to one Cr2+ and one P5+ atom. In the tenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cr2+ and one P5+ atom. In the eleventh O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Cr2+ and one P5+ atom. In the twelfth O2- site, O2- is bonded in a bent 150 degrees geometry to two P5+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mechanical and chemical properties of PVD and cold spray Cr-coatings on Zircaloy-4

In this paper, accident-tolerant fuel (ATF) cladding materials aim to improve fuel reliability and safety during accident scenarios in water-cooled reactors. These ATF cladding should also perform comparable or better than the current zirconium alloy cladding under reactor normal operating conditions. Surface-modified Zircaloy-4 was produced by depositing a protective coating of chromium by two different coating techniques, Physical Vapor Deposition (PVD) and Cold Spray (CS). The coating thickness, structure, composition, and mechanical properties of the coated Zircaloy were assessed with advanced materials characterization techniques. Results showed a strengthening effect of the Cr-coating, along with ~83% higher hardness compared to that of the Zircaloy-4 substrate. Surface topography and surface chemistry of the Cr-coated Zircaloy-4 were assessed with contact profilometry, atomic force microscopy, contact angle goniometry, and X-ray photoelectron spectroscopy. Deposited Cr-coating significantly improved surface wettability compared to the substrate Zircaloy-4. The formation of surface oxides on the coatings by prolonged exposure to ambient air showed a further increase in the hydrophobic behavior. Surface parameters and surface chemistry after flow boiling critical heat flux tests, conducted at atmospheric pressure, evidenced a slight increase in surface roughness with notable changes in wettability associated with the formation of surface oxides.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Revealing the chemical environment of Cr, Fe, and Ni in high temperature-ultrafine precipitate strengthened steel subjected to low fluence neutron irradiation

High-temperature ultrafine-precipitate-strengthened (HT-UPS) steel has potential applications in advanced nuclear reactors as a structural material. However, little is currently known about its response to neutron irradiation. This research provides insight into the neutron irradiation-induced physicochemical changes of the major constituents in HT-UPS steels, including Fe, Cr, and Ni, using synchrotron X-ray absorption near edge structure (XANES) and diffraction. This study is the first known investigation using XANES to characterize HT-UPS steel to analyze the evolution of the atomic level chemistry. It was found that following irradiation, nucleation, ballistic dispersion, and/or coarsening of Cr 23 C 6 precipitates occurred at very low neutron irradiation fluences, from 0.003 displacements per atom (dpa) up to 0.3 dpa, at ~600°C, which were at least an order of magnitude lower than previous studies. Calculations of the angular momentum projections, partial density of states, and the XANES spectra confirmed the experimental findings of the Cr 23 C 6 precipitate evolution. In contrast, the local atomic structure around Fe and Ni atoms demonstrated irradiation resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Advanced neutron absorber Ni-Cr-Mo-Gd alloys seawater corrosion mechanism and susceptibility study

Previous studies demonstrated the corrosion susceptibility of advanced neutron absorber (ANA) Ni-Cr-Mo-Gd in a seawater environment but remained inconclusive. In this paper, scanning electron microscopy was employed to identify the corrosion phase in Ni-Cr-Mo-Gd, and computational thermodynamic simulation was used to study phase corrosion potentials. Results showed that the Ni 5 Gd second phase, distributed along FCC grain boundaries in Ni-Cr-Mo-Gd, has lower corrosion potential than the substrate. Furthermore, heat treatment and alloy chemistry adjustment would not ameliorate the ANA corrosion susceptibility. Finally, isolating the Ni 5 Gd from the corrosion medium through advanced manufacturing is a viable way to improve the ANA corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effects of Minor Alloying Elements and Impurities on Long-Range Ordering in Ni-Cr-Based Alloys

There is growing concern about long-range ordered Ni2Cr phase forming during thermal aging of Ni-Cr-based alloys (e.g., 690, 625), which leads to lattice contraction, hardening, and embrittlement, possibly limiting the service life of light water reactor components. The timespan when this phase transformation occurs can vary in orders of magnitude between model and commercial alloys and is likely related to the presence of major (e.g., Fe, Mo) and minor alloying elements (e.g., Ti, Si, Nb). These minor alloying elements have been hypothesized to bind with vacancies and therefore limit diffusion. Contrarily, impurities (e.g., P, S) are believed to enhance vacancy diffusion and accelerate the Ni2Cr phase transformation because of a vacancy drag mechanism. This study implements experimental isothermal aging of model Ni-Cr binary and Ni-Cr-X ternary alloys, where X is Ti, Si, Nb, and P to help understand how each minor alloying element affects the Ni2Cr phase transformation timeline. Synchrotron-based X-ray diffraction and hardness measurements are used to quantify the evolution of the Ni2Cr phase transformation through a variety of short aging times to identify the onset of long-range order. These experimental results are compared to first principles simulations from literature to understand the mechanism by which each element impacts vacancy diffusion and the formation of the long-range ordered phase, Ni2Cr.

36 - MATERIALS SCIENCE↗
DOE OSTI2022

Polaronic Conductivity in Cr 2 Ge 2 Te 6 Single Crystals

We report that intrinsic 2D ferromagnetic semiconductors are an important class of materials for spin-charge conversion applications. Cr 2 Ge 2 Te 6 retains long-range magnetic order in the bilayer at cryogenic temperatures and shows complex magnetic interactions with considerable magnetic anisotropy. Here, a series of structural, magnetic, X-ray scattering, electronic, thermal transport and first-principles calculation studies are performed, which reveal that localized electronic charge carriers in Cr 2 Ge 2 Te 6 are dressed by the surrounding lattice and are involved in polaronic transport via hopping that is observed via magnetocrystalline anisotropy. This opens the possibility for manipulation of charge transport in Cr 2 Ge 2 Te 6 —based devices by electron–phonon- and spin–orbit coupling-based tailoring of polaron properties.

2D materials↗
DOE OSTI2024

Medium-Entropy Engineering of Magnetism in Layered Antiferromagnet Cu x Ni 2(1- x ) Cr x P 2 S 6

Antiferromagnetic van der Waals-type M 2 P 2 X 6 compounds provide a versatile material platform for studying 2D magnetism and relevant phenomena. Establishing ferromagnetism in 2D materials is technologically valuable. Though magnetism is generally tunable via a chemical way, it is challenging to induce ferromagnetism with isovalent chalcogen and bimetallic substitutions in M 2 P 2 X 6 . Here, we report co-substitution of Cu 1+ and Cr 3+ for Ni 2+ in Ni 2 P 2 S 6 , creating Cu x Ni 2(1-x) Cr x P 2 S 6 medium-entropy alloys spanning a full substitution range (x = 0 to 1). Such substitution strategy leads to a unique evolution in crystal structure and magnetic phases that are distinct from traditional isovalent bimetallic doping, with Cu and Cr co-substitution enhancing ferromagnetic correlations and generating a weak ferromagnetic phase in intermediate compositions. This aliovalent substitution strategy offers a universal approach for tuning layered magnetism in antiferromagnetic systems, which along with the potential for light-matter interaction and high-temperature ferroelectricity, can enable multifunctional device applications.

2D magnetism↗
DOE OSTI2022

High-pressure Cr 3+ R-line luminescence of zoisite and kyanite: a probe of octahedral site distortion

Here, the Cr 3+ luminescence spectra of zoisite and kyanite, two geologically important minerals, were studied up to 40 and 20 GPa, respectively, in various pressure media. Cr 3+ substitutes into the octahedral aluminum sites in both minerals and the R-line luminescence is a particularly sensitive site-specific probe of the octahedral Al site. Unlike many previous studies where Cr 3+ luminescence was utilized, both these minerals have multiple highly distorted octahedral sites resulting in very large splitting of their R-lines, ~ 300 cm -1 in zoisite and ~ 360 cm -1 in kyanite (for reference, ruby is 29 cm -1 ). For zoisite, the R-line splitting increases as pressure increases and more than triples from its ambient value by 40 GPa, while the R-line splitting in kyanite from the M1 and M2 sites does not change when compressed in a Ne pressure medium up to 20 GPa. We do not observe evidence of any phase transitions in either zoisite or kyanite across the pressure range of these new luminescence measurements. Furthermore, we present some high-pressure luminescence results where kyanite was known to be bridged between the diamond anvils and show how these spectra illustrate the different effect of uniaxial relative to hydrostatic stress on luminescence spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Stochastic Model for High Temperature Oxidation of Cr–Ni Austenitic Steels Assisted by Spallation

Abstract Cr–Ni austenitic steels offer significant high temperature corrosion protection by forming a surface oxide layer. However, above critical service conditions (temperature, atmosphere, thermal cycling), oxidized surface can experience intensive degradation because of scale spallation, which could be detrimental to the in-service life. To predict the effect of scale spallation on oxidation kinetics, a simulation was implemented using a stochastic model. The model considers topological parameters and intensity of spallation which can occur, while delivering a true oxidation constant. The experimental procedure identified the amount of formed spalled scale and topology of spallation based on the use of element mapping of the surface. This information was used to determine a true kinetic constant for a corresponding spallation intensity in oxidized Cr–Ni austenitic steel. To illustrate the capability of the stochastic model, a parametric analysis was performed. The model verified how the spallation parameters could change the oxidation processes from parabolic growth of an adhered oxide layer without spallation to a mixed linear-parabolic, or with a constant thickness of residual scale at high spallation intensity. The spallation model will be used in a separate article to characterize high temperature surface degradation of several Cr–Ni austenitic steels during harsh oxidation environments.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Temperature and dose rate effects on dislocation loop formation and decoration in self-ion irradiated high-purity Fe-Cr model alloys

Body-centered cubic (BCC) Fe-based alloys are promising candidate materials for advanced nuclear reactors. A widespread perception is that the addition of Cr favors the formation of ½ <111> dislocation loops. However, the Cr effects on dislocation loop formation/evolution remain unclear due to the limited experimental studies. In this study, we irradiate ultra-high purity bulk BCC Fe-xCr (x = 3, 5, and 8 wt%) with 6.7-8 MeV Fe ions over a wide range of temperatures (Tirr = 250-500 °C) and dose rates (10⁻⁵ to 10⁻³ dpa/s) to two midrange doses (0.35 and 3.5 dpa). The major irradiation-induced microstructures are loop decoration along non-screw dislocation lines at low temperatures and high dose rates as well as self-assembled loops at elevated temperatures. Post-irradiation Burgers vector analysis via g•b method on loops and electron tomography reveals that <001> preponderance is observable in all irradiated Fe-Cr samples at elevated temperature, resulting from stronger elastic energy originating from <001> edge.

Li, Yao [University of Tennessee (UT)]↗
DOE OSTI2025

Accelerated and heterogeneous corrosion of Cr-doped uranium nitride fuel pellets

The steam oxidation of Cr-doped UN fuel pellets is analyzed during sequential isothermal holds up to 720 °C. In situ neutron diffraction results show how Cr is accommodated in a secondary U 2 CrN 3 phase, leading to the formation of a duplex UN/U 2 CrN 3 microstructure. Under corrosion, the oxidation of the two phases begins at 400 °C for UN and 430 °C for U 2 CrN 3 , respectively. Because the UN phase is preferentially oxidized in the presence of U 2 CrN 3 , addition of Cr in UN based nuclear fuel is found to accelerate the corrosion rate. At 430 °C the oxidation of UN in the UN/U 2 CrN 3 microstructure is ~ 5 times faster than pure UN, increasing to ~19 times faster at 460 °C. The oxidation of U 2 CrN 3 produces UO 2 via the formation of two transient intermediate phases. In situ neutron diffraction enables oxidation processes of UN and U 2 CrN 3 components to be followed separately within the two-phase system.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Reassessing the proposed “CY chondrites”: Evidence for multiple meteorite types and parent bodies from Cr-Ti-H-C-N isotopes and bulk elemental compositions

Here, we report a coordinated bulk Cr-Ti-H-C-N isotopic and compositional study of six carbonaceous chondrites from Antarctica that are often considered to be related and termed Yamato-like carbonaceous (CY) chondrites. These meteorites are known to have undergone extensive aqueous alteration followed by different degrees of thermal alteration, to be similar to one another in regard to mineralogy, and share affinities with both the Ivuna-like carbonaceous (CI) and Mighei-like carbonaceous (CM) chondrites. While mineralogically similar, a key difference among these samples is that chondrules have been found in some of these samples, but not in others. The aim of this study is to evaluate the relationship of these meteorites to one another, and investigate how they relate to the CI and CM chondrite groups. We find that with the addition of the isotopic compositions of these ‘CY’ chondrites, there is now a continuum of isotopic compositions among the carbonaceous chondrites. The CI chondrites are no longer separate in O isotopic compositions from the other carbonaceous chondrite groups in plots of Cr-O and Ti-O. We also find that the ‘CY’ chondrites represent two distinct populations, which correlate with their heating stage. However, the peak temperatures experienced by each population can only explain the differences in H and C isotopes and abundances and N abundances between samples, and cannot have caused the differences in N, Cr, and Ti isotopes, or all the volatile element depletions of the sample’s bulk compositions. Instead, we conclude that the compositional and isotopic data of these two populations correlate with their known chondrule abundances, indicating distinct precursors for each population. We find it most likely that these samples originate from two distinct asteroids, implying that among the six samples studied here, there are not five related samples to constitute a new meteorite group. The chondrule-free heating Stage III samples are most likely heated CI chondrites, while the chondrule-bearing heating Stage IV samples could be heated CM chondrites.

58 GEOSCIENCES↗