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DOE OSTI2026

Nonequilibrium defect-phase nanostructures stabilized by irradiation in undersaturated Ni-Si nanocrystalline alloy

Nanocrystalline thin films of the undersaturated alloy Ni-8.5 at% Si were subjected to 2 MeV Ti irradiation at temperatures ranging from 450˚C to 550˚C. Correlative microscopy combining transmission electron microscopy (TEM), scanning-TEM and atom probe tomography (APT revealed that large dose irradiation at 450˚C of samples with initial grain sizes below 100 nm stabilized a novel nanostructure which surprisingly contained three co-existing phases, the γ face-centered-cubic (FCC) matrix, γ' L12 ordered precipitates on intragranular dislocation loops and Ni 31 Si 12 precipitates at triple junctions (TJs). In contrast, irradiation at 550˚C and irradiation of larger grain-size samples at 450˚C only produced a γ-γ' two-phase coexistence. Analysis of the three-phase nanostructure and phase field simulations indicates that radiation-induced segregation is most pronounced at TJs, thus triggering the formation of Ni 31 Si 12 precipitates. These incoherent precipitates, in turn, are expected to stabilize the grain size under irradiation. The results are generalized using the concept of driven defect-phases. It is suggested that the stabilization of driven defect-phases may impart radiation resilience by providing localized relaxation modes to the microstructure evolution during and after temporary perturbations in irradiation conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2023

An examination of the precipitation behavior of proton irradiated dual phase 308L weldment filler materials

Voids, G phase particles, and Ni-Si rich clusters in proton irradiated dual phase 308L groove filler of a SA508–304 L dissimilar metal weldment are analyzed using advanced characterization techniques. These weldments are often used in light water nuclear reactors and are subject to enhanced corrosion and associated stress corrosion cracking (SCC). Radiation damage is known to accelerate SCC. Ni-Si enriched clusters were observed in proton irradiated γ austenite, while G phase M 6 Ni 16 Si 7 (where M transition metal element) precipitates were observed in proton irradiated δ ferrite. Compositional analysis of the G phase precipitates and Ni-Si clusters from STEM-EDS and APT are compared. Unlike G phase particles in proton irradiated δ ferrite, Ni-Si clusters in proton irradiated γ austenite are not rich in Mn. Both STEM-EDS and APT line-scan profiles of the Ni-Si clusters show that the Fe and Cr concentration gradient between matrix γ austenite and the Ni-Si clusters is not as sharp as those between matrix δ ferrite and G phase. Further, HR-STEM imaging indicates that the lattice parameter of the Ni-Si clusters is commensurate with γ austenite and the clusters do not represent the precipitation of a second phase. Finally, our analysis demonstrates the density and volume fraction of G phase particles and the density of voids scales with proton irradiation damage and the energy to recoils.

308L groove filler↗

NASA NTRS1982

Processing of fused silicide coatings for carbon-based materials

The processing and oxidation resistance of fused Al-Si and Ni-Si slurry coatings on ATJ graphite was studied. Ni-Si coatings in the 70 to 90 percent Si range were successfully processed to melt, wet, and bond to the graphite. The molten coatings also infiltrated the porosity in graphite and reacted with it to form SiC in the coating. Cyclic oxidation at 1200 C showed that these coatings were not totally protective because of local attack of the substrate, due to the extreme thinness of the coatings in combination with coating cracks.

Smialek, J. L.↗

NASA NTRS1983

Processing of fused silicide coatings for carbon-based materials

Smialek, J. L.↗

DOE OSTI2020

Microstructural characterization of cold-worked 316 stainless steel flux thimble tubes irradiated up to 100 dpa in a commercial Pressurized Water Reactor

Two flux thimble tubes (FTT) made of 15% cold-worked 316 stainless steel (SS) were harvested from Ringhals Pressurized Water Reactor (PWR) Unit 2, with peak damages of 76 and 100 displacements per atom (dpa) after 29 and 34 years’ service, respectively. Specimens sectioned from parent tubes were comprehensively characterized with nominal damage levels of ~0, ~41, ~74, 76, and 100 dpa at a nominal temperature range of 285-323 °C. Both FTTs contained helium and hydrogen gases as transmutation products. The helium follows a production rate of ~9.8 appm/dpa, while environmental factors complicate hydrogen production obscuring an exact H/dpa ratio. Irradiation-induced dislocation loops, nano-cavities, solute clusters, and microsegregation were all observed. The dislocation loops and nano-cavities indicated saturation at 41 dpa. The solute clusters continued to evolve with Ni-Si clusters formed at 41 dpa, and Ni-Si-Mn-P clusters formed at 74 and 100 dpa, but neither clusters exhibited distinct diffraction patterns at any damage levels. Solute clusters were observed to frequently be co-located with dislocation loops, but fully decorated loops were rarely detected. Significant radiation-induced segregation (RIS) was observed around grain boundaries at all damage levels. The modified inverse Kirkendall (MIK) model captured the RIS behavior of major elements. Large cavities within or around an Mn-S rich region were observed for the first time. Through all the damage levels, void swelling is always below 0.05%, making significant dimensional change unlikely in core internals when used at similar conditions. Meanwhile, the role of overwhelming nanocavities, presumably helium bubbles, should be considered in other potential degradation mechanisms, including irradiation-assisted stress corrosion cracking, embrittlement, and loss of fracture toughness, which remain the concerns for extended operation of nuclear power plants.

Post Irradiation Examination, Isotope Dilution Mas↗

NASA NTRS1977

The chemical composition of the cores of the terrestrial planets and the moon

Using models of the quasi-chemical theory of solutions, the activity coefficients of silicon are calculated in the melts Fe-Si, Ni-Si, and Fe-Ni-Si. The calculated free energies of solution of liquid nickel and silicon in liquid iron in the interval 0 to 1400 kbar and 1500 to 4000 K, shows that Fe-Ni-Si alloy is stable under the conditions of the outer core of the earth and the cores of the terrestrial planets. The oxidation-reduction conditions are studied, and the fugacity of oxygen in the mantles of the planets and at the core-mantle boundary are calculated. The mechanism of reduction of silicon is analyzed over a broad interval of p and T. The interaction between the matter of the core and mantle is studied, resulting in the extraction of silicon from the mantle and its solution in the material of the core. It is concluded that silicon can enter into the composition of the outer core of the earth and Venus, but probably does not enter into the composition of the cores of Mercury, Mars, and the moon, if in fact the latter possesses one.

Kuskov, O. L.↗

NASA NTRS1981

Metal-semiconductor interfacial reactions - Ni/Si system

X-ray photoelectron spectroscopy and channeling measurements with MeV He-4(+) ions have been used to probe the structure of the interface in the Ni/Si system. It is found that reactions occur where Ni is deposited on Si at 10 to the -10th torr: Si atoms are displaced from lattice sites, the Ni atoms are in an Si-rich environment, and the Ni/Si interface is graded in composition. Composition gradients are present at both interfaces in the Si/Ni2/Si/Ni system. For the Ni-Si system, cooling the substrate to 100 K slows down the reaction rate. The temperature dependence of the interfacial reactivity indicates the kinetic nature of metal-semiconductor interfaces.

Cheung, N. W.↗

NASA NTRS1985

Oxidation resistant slurry coating for carbon-based materials

An oxidation resistant coating is produced on carbon-base materials, and the same processing step effects an infiltration of the substrate with silicon containing material. The process comprises making a slurry of nickel and silicon powders in a nitrocellulose lacquer, spraying onto the graphite or carbon-carbon substrate, and sintering in vacuum to form a fused coating that wets and covers the surface as well as penetrates into the pores of the substrate. Optimum wetting and infiltration occurs in the range of Ni-60 w/o Si to Ni-90 w/o Si with deposited thicknesses of 25-100 mg/sq. cm. Sintering temperatures of about 1200 C to about 1400 C are used, depending on the melting point of the specific coating composition. The sintered coating results in Ni-Si intermetallic phases and SiC, both of which are highly oxidation resistant.

Smialek, J. L.↗

DOE OSTI2021

Modified microstructures in proton irradiated dual phase 308L weldment filler material

In this study, the effect of proton irradiation on the microstructure of δ ferrite—γ austenite mixed phase 308L filler material in a 508–304 dissimilar metal weldment was investigated over a depth of 0 to 10 µm. Ni–Si–Mn G-phase precipitates were observed with SEM and TEM in δ ferrite but not in γ austenite. Our density functional theory based calculations show that the G/Fe interface energy in δ-Fe is significantly lower than that in γ-Fe (0.35 versus 1.25 J/m 2 ), which provides a thermodynamics-based explanation for our experimental observations of preferential formation of G-phase in δ ferrite. STEM-EDS, TEM dark field imaging, and diffraction patterns confirmed the Ni–Si–Mn enriched precipitates were G-phase precipitates with a stoichiometry of Mn 6 Ni 16 Si 7 . Intragranular voids and Ni–Si enriched clusters were observed in irradiated γ austenite. Additionally, Ni and Si segregation was observed along the void interfaces. In both cases, Ni–Si clusters and segregation to voids, selected area diffraction patterns did not reveal the existence of a second phase. Proton irradiation induced Cr depletion and Si and Ni enrichment at γ-γ austenite grain boundaries that was characterized with STEM/EDS.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2020

Materials Data on SiNi2 by Materials Project

Ni2Si is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded in a 4-coordinate geometry to five equivalent Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.31–2.72 Å. In the second Ni2+ site, Ni2+ is bonded to five equivalent Si4- atoms to form a mixture of distorted edge and corner-sharing NiSi5 square pyramids. There are a spread of Ni–Si bond distances ranging from 2.34–2.58 Å. Si4- is bonded in a 10-coordinate geometry to ten Ni2+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Si2Ni by Materials Project

NiSi2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ni is bonded in a body-centered cubic geometry to eight equivalent Si atoms. All Ni–Si bond lengths are 2.35 Å. Si is bonded to four equivalent Ni and six equivalent Si atoms to form a mixture of distorted corner, edge, and face-sharing SiSi6Ni4 tetrahedra. All Si–Si bond lengths are 2.72 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Si12Ni31 by Materials Project

Ni31Si12 crystallizes in the trigonal P321 space group. The structure is three-dimensional. there are eight inequivalent Ni+1.55+ sites. In the first Ni+1.55+ site, Ni+1.55+ is bonded in a 5-coordinate geometry to five Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.31–2.88 Å. In the second Ni+1.55+ site, Ni+1.55+ is bonded to five Si4- atoms to form a mixture of edge and corner-sharing NiSi5 trigonal bipyramids. There are three shorter (2.33 Å) and two longer (2.57 Å) Ni–Si bond lengths. In the third Ni+1.55+ site, Ni+1.55+ is bonded to four Si4- atoms to form distorted NiSi4 tetrahedra that share corners with twelve NiSi4 tetrahedra, a cornercorner with one NiSi5 trigonal bipyramid, edges with three equivalent NiSi4 tetrahedra, and a faceface with one NiSi4 tetrahedra. There are one shorter (2.38 Å) and three longer (2.43 Å) Ni–Si bond lengths. In the fourth Ni+1.55+ site, Ni+1.55+ is bonded to four Si4- atoms to form a mixture of edge and corner-sharing NiSi4 tetrahedra. There are three shorter (2.43 Å) and one longer (2.49 Å) Ni–Si bond lengths. In the fifth Ni+1.55+ site, Ni+1.55+ is bonded to four Si4- atoms to form NiSi4 tetrahedra that share corners with nine NiSi4 tetrahedra, corners with three equivalent NiSi5 trigonal bipyramids, and edges with three equivalent NiSi4 tetrahedra. There are three shorter (2.31 Å) and one longer (2.53 Å) Ni–Si bond lengths. In the sixth Ni+1.55+ site, Ni+1.55+ is bonded in a distorted trigonal non-coplanar geometry to three Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.30–2.40 Å. In the seventh Ni+1.55+ site, Ni+1.55+ is bonded to four Si4- atoms to form NiSi4 tetrahedra that share corners with thirteen NiSi4 tetrahedra, a cornercorner with one NiSi5 trigonal bipyramid, and edges with five NiSi4 tetrahedra. There are a spread of Ni–Si bond distances ranging from 2.30–2.48 Å. In the eighth Ni+1.55+ site, Ni+1.55+ is bonded to four Si4- atoms to form distorted NiSi4 tetrahedra that share corners with thirteen NiSi4 tetrahedra, edges with four NiSi4 tetrahedra, and an edgeedge with one NiSi5 trigonal bipyramid. There are a spread of Ni–Si bond distances ranging from 2.24–2.40 Å. There are five inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 11-coordinate geometry to eleven Ni+1.55+ atoms. In the second Si4- site, Si4- is bonded in a distorted q6 geometry to ten Ni+1.55+ atoms. In the third Si4- site, Si4- is bonded in a 10-coordinate geometry to ten Ni+1.55+ atoms. In the fourth Si4- site, Si4- is bonded in a 10-coordinate geometry to ten Ni+1.55+ atoms. In the fifth Si4- site, Si4- is bonded in a 9-coordinate geometry to eleven Ni+1.55+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Si2Ni3 by Materials Project

Ni3Si2 crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. there are eight inequivalent Ni+2.67+ sites. In the first Ni+2.67+ site, Ni+2.67+ is bonded in a 6-coordinate geometry to six Si4- atoms. There are four shorter (2.34 Å) and two longer (2.42 Å) Ni–Si bond lengths. In the second Ni+2.67+ site, Ni+2.67+ is bonded in a 4-coordinate geometry to six Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.28–2.74 Å. In the third Ni+2.67+ site, Ni+2.67+ is bonded in a 4-coordinate geometry to six Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.28–2.74 Å. In the fourth Ni+2.67+ site, Ni+2.67+ is bonded to six Si4- atoms to form a mixture of distorted face and corner-sharing NiSi6 octahedra. The corner-sharing octahedra tilt angles range from 63–64°. There are a spread of Ni–Si bond distances ranging from 2.26–2.46 Å. In the fifth Ni+2.67+ site, Ni+2.67+ is bonded to six Si4- atoms to form a mixture of distorted face, edge, and corner-sharing NiSi6 octahedra. The corner-sharing octahedra tilt angles range from 47–64°. There are a spread of Ni–Si bond distances ranging from 2.30–2.64 Å. In the sixth Ni+2.67+ site, Ni+2.67+ is bonded in a 5-coordinate geometry to five Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.26–2.54 Å. In the seventh Ni+2.67+ site, Ni+2.67+ is bonded in a distorted pentagonal planar geometry to five Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.30–2.51 Å. In the eighth Ni+2.67+ site, Ni+2.67+ is bonded in a distorted pentagonal planar geometry to five Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.30–2.52 Å. There are five inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 5-coordinate geometry to five Ni+2.67+ atoms. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to nine Ni+2.67+ atoms. In the third Si4- site, Si4- is bonded in a 8-coordinate geometry to eight Ni+2.67+ atoms. In the fourth Si4- site, Si4- is bonded in a 8-coordinate geometry to eight Ni+2.67+ atoms. In the fifth Si4- site, Si4- is bonded in a 11-coordinate geometry to ten Ni+2.67+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on SiNi by Materials Project

NiSi is Modderite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ni4+ is bonded to six equivalent Si4- atoms to form a mixture of distorted corner, edge, and face-sharing NiSi6 pentagonal pyramids. There are a spread of Ni–Si bond distances ranging from 2.28–2.40 Å. Si4- is bonded in a 8-coordinate geometry to six equivalent Ni4+ and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.66 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on SiNi2 by Materials Project

Ni2Si crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded to five equivalent Si4- atoms to form NiSi5 trigonal bipyramids that share corners with twelve equivalent NiSi6 octahedra, corners with eight equivalent NiSi5 trigonal bipyramids, edges with six equivalent NiSi5 trigonal bipyramids, and faces with six equivalent NiSi6 octahedra. The corner-sharing octahedra tilt angles range from 29–61°. There are three shorter (2.25 Å) and two longer (2.49 Å) Ni–Si bond lengths. In the second Ni2+ site, Ni2+ is bonded to six equivalent Si4- atoms to form NiSi6 octahedra that share corners with twelve equivalent NiSi6 octahedra, corners with twelve equivalent NiSi5 trigonal bipyramids, edges with six equivalent NiSi6 octahedra, faces with two equivalent NiSi6 octahedra, and faces with six equivalent NiSi5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 52°. All Ni–Si bond lengths are 2.57 Å. Si4- is bonded in a 11-coordinate geometry to eleven Ni2+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on SiNi3 by Materials Project

Ni3Si is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ni+1.33+ is bonded in a square co-planar geometry to four equivalent Si4- atoms. All Ni–Si bond lengths are 2.47 Å. Si4- is bonded to twelve equivalent Ni+1.33+ atoms to form a mixture of corner and face-sharing SiNi12 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on SiNi by Materials Project

NiSi is gamma CuTi structured and crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. Ni4+ is bonded in a 6-coordinate geometry to six equivalent Si4- atoms. There are a spread of Ni–Si bond distances ranging from 2.34–2.39 Å. Si4- is bonded in a 10-coordinate geometry to six equivalent Ni4+ and four equivalent Si4- atoms. All Si–Si bond lengths are 2.67 Å.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on SiNi3 by Materials Project

Ni3Si crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three nickel molecules and three Ni2Si sheets oriented in the (0, 0, 1) direction. In each Ni2Si sheet, Ni+1.33+ is bonded in a 3-coordinate geometry to three equivalent Si4- atoms. All Ni–Si bond lengths are 2.34 Å. Si4- is bonded to six equivalent Ni+1.33+ and six equivalent Si4- atoms to form a mixture of edge, face, and corner-sharing SiSi6Ni6 cuboctahedra. All Si–Si bond lengths are 2.59 Å.

36 MATERIALS SCIENCE↗