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All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Structure and energetics of Cr(CO)6 and Cr(CO)5

The geometric structures and energetics of Cr(CO)6 and Cr(CO)5 are determined at the modified coupled-pair functional, single and double excitation coupled-cluster (CCSD), and CCSD(T) levels of theory. For Cr(CO)6, the structure and force constants for the totally symmetric representation are in good agreement with experimental data once basis set constants are taken into account. In the largest basis set at the CCSD(T) level of theory, the total binding energy of CR(CO)6 is estimated at around 140 kcal/mol, or about 86 percent of the experimental value. In contrast, the first bond energy of Cr(CO)6 is very well described at the CCSD(T) level of theory, with the best estimated value of 38 kcal/mol being within the experimental uncertainty.

Barnes, Leslie A.↗
NASA NTRS1992

The structure and energetics of Cr(CO)6 and Cr(CO)5

The geometric structure of Cr(CO)6 is optimized at the modified coupled pair functional (MCPF), single and double excitation coupled-cluster (CCSD) and CCSD(T) levels of theory (including a perturbational estimate for connected triple excitations), and the force constants for the totally symmetric representation are determined. The geometry of Cr(CO)5 is partially optimized at the MCPF, CCSD, and CCSD(T) levels of theory. Comparison with experimental data shows that the CCSD(T) method gives the best results for the structures and force constants, and that remaining errors are probably due to deficiencies in the one-particle basis sets used for CO. The total binding energies of Cr(CO)6 and Cr(CO)5 are also determined at the MCPF, CCSD, and CCSD(T) levels of theory. The CCSD(T) method gives a much larger total binding energy than either the MCPF or CCSD methods. An analysis of the basis set superposition error (BSSE) at the MCPF level of treatment points out limitations in the one-particle basis used. Calculations using larger basis sets reduce the BSSE, but the total binding energy of Cr(CO)6 is still significantly smaller than the experimental value, although the first CO bond dissociation energy of Cr(CO)6 is well described. An investigation of 3s3p correlation reveals only a small effect. In the largest basis set, the total CO binding energy of Cr(CO)6 is estimated to be 140 kcal/mol at the CCSD(T) level of theory, or about 86 percent of the experimental value. The remaining discrepancy between the experimental and theoretical value is probably due to limitations in the one-particle basis, rather than limitations in the correlation treatment. In particular an additional d function and an f function on each C and O are needed to obtain quantitative results. This is underscored by the fact that even using a very large primitive set (1042 primitive functions contracted to 300 basis functions), the superposition error for the total binding energy of Cr(CO)6 is 22 kcal/mol at the MCPF level of treatment.

Barnes, Leslie A.↗
DOE OSTI2020

Materials Data on Cr(CO)6 by Materials Project

Cr(CO)6 is beta Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four Cr(CO)6 clusters. Cr3+ is bonded in an octahedral geometry to six O2- atoms. There are one shorter (2.00 Å) and five longer (2.02 Å) Cr–O bond lengths. There are four inequivalent C+1.50+ sites. In the first C+1.50+ site, C+1.50+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.16 Å. In the second C+1.50+ site, C+1.50+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.16 Å. In the third C+1.50+ site, C+1.50+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.16 Å. In the fourth C+1.50+ site, C+1.50+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.16 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to one Cr3+ and one C+1.50+ atom. In the second O2- site, O2- is bonded in a linear geometry to one Cr3+ and one C+1.50+ atom. In the third O2- site, O2- is bonded in a linear geometry to one Cr3+ and one C+1.50+ atom. In the fourth O2- site, O2- is bonded in a linear geometry to one Cr3+ and one C+1.50+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cr(CO)6 by Materials Project

Cr(CO)6 is beta Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four Cr(CO)6 clusters. Cr3+ is bonded in an octahedral geometry to six C+1.50+ atoms. There is four shorter (1.92 Å) and two longer (1.93 Å) Cr–C bond length. There are four inequivalent C+1.50+ sites. In the first C+1.50+ site, C+1.50+ is bonded in a distorted linear geometry to one Cr3+ and one O2- atom. The C–O bond length is 1.16 Å. In the second C+1.50+ site, C+1.50+ is bonded in a distorted linear geometry to one Cr3+ and one O2- atom. The C–O bond length is 1.16 Å. In the third C+1.50+ site, C+1.50+ is bonded in a distorted linear geometry to one Cr3+ and one O2- atom. The C–O bond length is 1.16 Å. In the fourth C+1.50+ site, C+1.50+ is bonded in a distorted linear geometry to one Cr3+ and one O2- atom. The C–O bond length is 1.16 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one C+1.50+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one C+1.50+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one C+1.50+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one C+1.50+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1991

An ab initio study of Fe(CO)n, n = 1,5, and Cr(CO)6

Ab initio calculations have been performed for Cr(CO)6 and Fe(CO)n, n = 1,5. Basis sets of better than double zeta quality are used, and correlation is included using the modified coupler-pair functional method. The computed geometries and force constants are in reasonable agreement with experiment. The sequential bond dissociation energies of CO from Fe(CO)5 are estimated to be: 39, 31, 25, 22, and greater than 5 kcal/mol. It is noted that the first bond dissociation energy is relative to the singlet ground state of Fe(CO)5 and the lowest singlet state of Fe(CO)4, whereas the second is relative to the ground triplet states of Fe(CO)4 and Fe(CO)3. In addition, the binding energy for Fe-CO would be modified to 18 kcal/mol if dissociation occurred to the Fe(5F) excited state asymptote. The CO binding energies for Fe and Cr are found to be in poorer agreement with experiment than those found in a previous study on Ni(CO)4. The origins of this difference are discussed.

Barnes, Leslie A.↗
NASA NTRS1994

Computational studies of metal-metal and metal-ligand interactions

Accurate calculations on the bond length, dipole moment, and harmonic frequency of CO are presented, using large basis sets and high levels of electron correlation. The geometric structure, force constants and binding energies of Cr(CO)6 and Cr(CO)5 are computed using large basis sets and high levels of electron correlation. The molecule O4(+) is studied, using large basis sets and high levels of electron correlation, including the CASSCF, CASSI,and CASPT2 methods. Binding energies, geometries and frequencies are computed. Symmetry breaking is a particular problem for the antisymmetric stretch, which is addressed using the CASSI method. The symmetry breaking problem in O4(+) has also been studied using the Brueckner coupled-cluster method. This gives results in good agreement with CASSI. A multi-region numerical integration scheme is investigated for use in Density Functional Calculations. This scheme is found to give comparable results to a widely used scheme based on the Euler-Maclaurin technique.

Barnes, Leslie A.↗
NASA NTRS1992

Computational studies of metal-metal and metal-ligand interactions

The geometric structure of Cr(CO)6 is optimized at the modified coupled-pair functional (MCPF), single and double excitation coupled-cluster (CCSD) and CCSD(T) levels of theory (including a perturbational estimate for connected triple excitations), and the force constants for the totally symmetric representation are determined. The geometry of Cr(CO)5 is partially optimized at the MCPF, CCSD and CCSD(T) levels of theory. Comparison with experimental data shows that the CCSD(T) method gives the best results for the structures and force constants, and that remaining errors are probably due to deficiencies in the one-particle basis sets used for CO. A detailed comparison of the properties of free CO is therefore given, at both the MCPF and CCSD/CCSD(T) levels of treatment, using a variety of basis sets. With very large one-particle basis sets, the SSCD(T) method gives excellent results for the bond distance, dipole moment and harmonic frequency of free CO. The total binding energies of Cr(CO)6 and Cr(CO)5 are also determined at the MCPF, CCSD and CCSD(T) levels of theory. The CCSD(T) method gives a much larger total binding energy than either the MCPF or CCSD methods. An analysis of the basis set superposition error (BSSE) at the MCPF level of treatment points out limitations in the one-particle basis used here and in a previous study. Calculations using larger basis sets reduced the BSSE, but the total binding energy of Cr(CO)6 is still significantly smaller than the experimental value, although the first CO bond dissociation energy of Cr(CO)6 is well described. An investigation of 3s3p correlation reveals only a small effect. The remaining discrepancy between the experimental and theoretical total binding energy of Cr(CO)6 is probably due to limitations in the one-particle basis, rather than limitations in the correlation treatment. In particular an additional d function and an f function on each C and O are needed to obtain quantitative results. This is underscored by the fact that even using a very large primitive se (1042 primitive functions contracted to 300 basis functions), the superposition error for the total binding energy of Cr(CO)6 is 22 kcal/mol at the MCPF level of treatment.

Barnes, Leslie A.↗
NASA NTRS1994

Computational studies of metal-metal and metal-ligand interactions

Accurate calculations on the bond length, dipole moment, and harmonic frequency of CO are presented, using large basis sets and high levels of electron correlation. The geometric structure, force constants and binding energies of Cr(C0)6 and Cr(CO)5 are computed using large basis sets and high levels of electron correlation. The molecule 04(+) is studied, using large basis sets and high levels of electron correlation, including the CASSCF, CASSI and CASPT2 methods. Binding energies, geometries and frequencies are computed. Symmetry breaking is a particular problem for the antisymmetric stretch, which is addressed using the CASSI method. The symmetry breaking problem in 04(+) has also been studied using the Brueckner coupled cluster method. This gives results in good agreement with CASSI. A multi-region numerical integration scheme is investigated for use in Density Functional Calculations. This scheme is found to give comparable results to a widely used scheme based on the Euler-Maclaurin technique.

Barnes, Leslie A.↗
DOE OSTI2020

Localized Corrosion Behavior of Non-Equiatomic NiFeCrMnCo Multi-Principal Element Alloys

A series of single phase Ni 38 Fe 20 Cr x Mn 21–0.5x Co 21–0.5x multi-principal element alloys (MPEAs) were fabricated and their localized corrosion behavior was tested in 0.6 M NaCl solution. These MPEAs were found to be susceptible to localized corrosion, exhibiting pitting at room temperature, as indicated by positive hysteresis loops and low repassivation potentials observed in cyclic potentiodynamic polarization experiments. The pitting resistance increased with increasing Cr content. Interestingly, even the MPEAs with low chromium content, Ni 38 Fe 20 Cr 6 Mn 18 Co 18 and Ni 38 Fe 20 Cr 10 Mn 16 Co 16 , exhibited passivity and localized corrosion. Here, the passivity observed in these low chromium MPEAs is likely derived from their relatively high nickel content. Crystallographic pit morphology was observed in most of these MPEAs, suggesting the absence of a salt film on the dissolving pit surface. Such crystallographic pit morphology indicates that the pit growth in most of these MPEAs was under charge-transfer/ohmic control.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Selective Oxidation and Cr Segregation in High-Entropy Oxide Thin Films

High-entropy oxides (HEOs) offer exceptional compositional flexibility and structural stability, making them promising materials for energy and catalytic applications. Here, in this study, we investigate Sr doping effects on B-site cation oxidation states, local composition, and structure in epitaxial La 1–x Sr x (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )O 3 thin films. X-ray spectroscopies reveal that Sr doping preferentially promotes Cr oxidation from Cr 3+ to Cr 6+ , partially oxidizes Co and Ni, while leaving Mn 4+ and Fe 3+ unchanged. Atomic-resolution scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy shows pronounced Cr segregation, with depletion at the interface and enrichment at the surface, along with partial amorphization in heavily Sr-doped samples. This segregation is likely driven by oxidation-induced migration of smaller, high-valence Cr cations during growth. These findings highlight the critical interplay between charge compensation, local strain, and compositional fluctuations in HEOs, indicating that precise control over growth conditions is critical for tuning their surface composition and electronic structure toward more robust electrocatalyst design.

36 MATERIALS SCIENCE↗
NASA NTRS1984

The effects of Cr, Co, Al, Mo and Ta on the cyclic oxidation behavior of a prototype cast Ni-base superalloy based on a 2(5) composite statistically designed experiment

A series of cast Ni-base superalloys were systematically varied at selected levels of Co, Cr, Mo, Ta, and Al. The elemental levels varied were Mo, 0 to 4 percent; Cr, 6 to 18 percent; Co, 0 to 20 percent, Ta, 0 to 8 percent; and Al, 3.25 to 6.25 percent. The cyclic oxidation resistance was determined from specific weight change data as a function of time for 1 hr cycles in static air at 1100 C. The significant terms in decreasing order of their importance were Al, Ta, Cr2, Al-Cr, Cr-Co, Co2, Al-Mo, Cr-Mo, Al-Al, and Mo-Ta. The Al term alone accounted for close to 82 percent of the explained variability. The estimating equation showed that the Al level was the most important and should be at its 6.25 wt % maximum value. The Mo and Ta levels should also be at their maximum 4 and 8 wt % respectively. The cobalt composition should be as low as possible, i.e., 0 wt%. The Cr level optimum varies depending on the other 4 levels. The X-ray diffaction results indicate the most protective scales are alumina/aluminate spinel stabilizized with a tri-rutile oxide high in Ta and Mo.

Barrett, C. A.↗
NASA NTRS2010

Rocket-Plume Spectroscopy Simulation for Hydrocarbon-Fueled Rocket Engines

The UV-Vis spectroscopic system for plume diagnostics monitors rocket engine health by using several analytical tools developed at Stennis Space Center (SSC), including the rocket plume spectroscopy simulation code (RPSSC), to identify and quantify the alloys from the metallic elements observed in engine plumes. Because the hydrocarbon-fueled rocket engine is likely to contain C2, CO, CH, CN, and NO in addition to OH and H2O, the relevant electronic bands of these molecules in the spectral range of 300 to 850 nm in the RPSSC have been included. SSC incorporated several enhancements and modifications to the original line-by-line spectral simulation computer program implemented for plume spectral data analysis and quantification in 1994. These changes made the program applicable to the Space Shuttle Main Engine (SSME) and the Diagnostic Testbed Facility Thruster (DTFT) exhaust plume spectral data. Modifications included updating the molecular and spectral parameters for OH, adding spectral parameter input files optimized for the 10 elements of interest in the spectral range from 320 to 430 nm and linking the output to graphing and analysis packages. Additionally, the ability to handle the non-uniform wavelength interval at which the spectral computations are made was added. This allowed a precise superposition of wavelengths at which the spectral measurements have been made with the wavelengths at which the spectral computations are done by using the line-by-line (LBL) code. To account for hydrocarbon combustion products in the plume, which might interfere with detection and quantification of metallic elements in the spectral region of 300 to 850 nm, the spectroscopic code has been enhanced to include the carbon-based combustion species of C2, CO, and CH. In addition, CN and NO have spectral bands in 300 to 850 nm and, while these molecules are not direct products of hydrocarbon-oxygen combustion systems, they can show up if nitrogen or a nitrogen compound is present as an impurity in the propellants and/or these can form in the boundary layer as a result of interaction of the hot plume with the atmosphere during the ground testing of engines. Ten additional electronic band systems of these five molecules have been included into the code. A comprehensive literature search was conducted to obtain the most accurate values for the molecular and the spectral parameters, including Franck-Cordon factors and electronic transition moments for all ten band systems. For each elemental transition in the RPSSC, six spectral parameters - Doppler broadened line width at half-height, pressure-broadened line width at half-height, electronic multiplicity of the upper state, electronic term energy of the upper state, Einstein transition probability coefficient, and the atomic line center - are required. Input files have been created for ten elements of Ni, Fe, Cr, Co, Cu, Ca, Mn, Al, Ag, and Pd, which retain only relatively moderate to strong transitions in 300 to 430 nm spectral range for each element. The number of transitions in the input files is 68 for Ni; 148 for Fe; 6 for Cr; 87 for Co; 1 for Ca; 3 for Mn; 2 each for Cu, Al, and Ag; and 11 for Pd.

Tejwani, Gopal D.↗
DOE OSTI2025

Temperature-Dependent Mechanical Properties of Ni-Based Concentrated Alloys: Insights from First-Principles Calculations

The present work focuses on predicting temperature-dependent mechanical properties of Ni-based concentrated alloys Ni 18 Cr 10 Co 10 Fe 6 M 4 (abbreviated by X 44 M 4 , with M = Al, V, Mn, Fe, Nb, Mo, and W) using density functional theory (DFT). These predictions are based on shear (plastic) and elastic deformations, utilizing the special quasirandom structure (SQS), the phonon-based quasiharmonic approach (QHA), and the quasistatic approach. The resulting properties include coefficient of thermal expansion via QHA, ideal shear strength (τ IS ), and stable and unstable stacking fault energies (γ SF and γ US ) through pure alias shear deformation, and elastic constants (c ij ), bulk modulus (B 0 ), and shear modules (G 0 ) via elastic deformation. Notably, predicting accurate γ SF is challenging due to uncertainties that can exceed the γ SF values. τ IS and γ US exhibit a strong linear relationship, enabling the accurate prediction of γ US based on the precisely determined τ IS . All mechanical properties of X 44 M 4 decrease with increasing temperature, except for some γ SF cases such as X 44 M 4 with M = V, Mn, Fe, Mo, and W. Among the X 44 M 4 alloys, X 44 Nb 4 exhibits the lowest τ IS , γ US , and G 0 values, and the highest B 0 /G 0 ratio, while X 44 Mn 4 has the lowest B 0 and B 0 /G 0 ratio. We found that volume is a crucial descriptor for understanding and modeling mechanical properties (except B0 and maybe also γ SF ) affected by alloying elements and temperature. Ni-based dilute alloys (e.g., Ni 11 M 1 and Ni 31 M 1 ) and concentrated alloys (e.g., X 44 M 4 ) show similar trends in mechanical properties influenced by alloying elements and temperature, simplifying the analysis and design of Ni-based alloys.

Elastic properties↗
DOE OSTI2020

One-electron redox kinetics of aqueous transition metal couples Zn 2+/+ , Co 2+/+ , and Ni 2+/+ using pulse radiolysis

The one-electron redox potentials for aqueous metal couples Co 2+/+ and Ni 2+/+ have been investigated by using pulse radiolysis using their reactions with a series of reference compounds to establish the most positive upper limits of E 0 . Experiments with Zn + were also carried out to confirm the characteristic shape of the expected reduction kinetics. Both formate ions and t-BuOH were employed to scavenge ˙OH radicals and ˙H atoms. Kinetics and fitted first and second order reaction rates have been reported for reactions with methyl viologen, fluorescein, Ru(NH 3 ) 6 3+ , Co(en) 3 2+ , Co(sepulcrate) 3+ , Ru(bpy) 3 2+ , Cr(bpy)33+, and Ni(Me 6 [14]4,11-dieneN4) 2+ . Previous work demonstrated that both Co 2+ and Ni 2+ can be reduced by CO 2 ˙- radicals, giving a negative E 0 limit of -1.9 V vs. SHE. A definite reaction of Ni + with fluorescein di-anions provides a new upper limit of the Ni 2+/+ couple as -0.906 V vs. SHE. The reaction of Co + with Ru(bpy) 3 2+ has been confirmed, giving E 0 = -1.3 V vs. SHE as a rigorous upper limit of the Co 2+/+ couple. In the case of Co 2+/+ , kinetics were complicated by a self-catalyzed metal clustering phenomenon. Initiation rate constants of this process have also been reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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 OSTI2020

Real-time observations of TRIP-induced ultrahigh strain hardening in a dual-phase CrMnFeCoNi high-entropy alloy

Abstract Strategies involving metastable phases have been the basis of the design of numerous alloys, yet research on metastable high-entropy alloys is still in its infancy. In dual-phase high-entropy alloys, the combination of local chemical environments and loading-induced crystal structure changes suggests a relationship between deformation mechanisms and chemical atomic distribution, which we examine in here in a Cantor-like Cr 20 Mn 6 Fe 34 Co 34 Ni 6 alloy, comprising both face-centered cubic ( fcc ) and hexagonal closed packed ( hcp ) phases. We observe that partial dislocation activities result in stable three-dimensional stacking-fault networks. Additionally, the fraction of the stronger hcp phase progressively increases during plastic deformation by forming at the stacking-fault network boundaries in the fcc phase, serving as the major source of strain hardening. In this context, variations in local chemical composition promote a high density of Lomer-Cottrell locks, which facilitate the construction of the stacking-fault networks to provide nucleation sites for the hcp phase transformation.

36 MATERIALS SCIENCE↗
NASA NTRS2012

Compositional Effects on Nickel-Base Superalloy Single Crystal Microstructures

Fourteen nickel-base superalloy single crystals containing 0 to 5 wt% chromium (Cr), 0 to 11 wt% cobalt (Co), 6 to 12 wt% molybdenum (Mo), 0 to 4 wt% rhenium (Re), and fixed amounts of aluminum (Al) and tantalum (Ta) were examined to determine the effect of bulk composition on basic microstructural parameters, including gamma' solvus, gamma' volume fraction, volume fraction of topologically close-packed (TCP) phases, phase chemistries, and gamma - gamma'. lattice mismatch. Regression models were developed to describe the influence of bulk alloy composition on the microstructural parameters and were compared to predictions by a commercially available software tool that used computational thermodynamics. Co produced the largest change in gamma' solvus over the wide compositional range used in this study, and Mo produced the largest effect on the gamma lattice parameter and the gamma - gamma' lattice mismatch over its compositional range, although Re had a very potent influence on all microstructural parameters investigated. Changing the Cr, Co, Mo, and Re contents in the bulk alloy had a significant impact on their concentrations in the gamma matrix and, to a smaller extent, in the gamma' phase. The gamma phase chemistries exhibited strong temperature dependencies that were influenced by the gamma and gamma' volume fractions. A computational thermodynamic modeling tool significantly underpredicted gamma' solvus temperatures and grossly overpredicted the amount of TCP phase at 982 C. Furthermore, the predictions by the software tool for the gamma - gamma' lattice mismatch were typically of the wrong sign and magnitude, but predictions could be improved if TCP formation was suspended within the software program. However, the statistical regression models provided excellent estimations of the microstructural parameters based on bulk alloy composition, thereby demonstrating their usefulness.

MacKay, Rebecca A.↗
DOE OSTI2023

Investigation of the ordered and disordered corrosion morphologies on Ni-based alloy in the passive state

We report an order and disorder combined corrosion morphology of dual-phase Ni-based alloy in the passive state. After galvanostatic polarization in the passive region, the surface of the γ(Ni) phase presents amorphous feature while that of the γ′(Ni 3 Al) phase maintains crystalline. The variations in weight percentages of Ni (50.19% → 3.80%), Co (19.24% → 0.65%), Ta (0.85% → 21.19%), and W (5.73% → 43.79%) of γ surface are evident, whereas the composition of γ′ surface is nearly unchanged. The passive film comprises $W^{6+}_{ox}$, $Ta^{5+}_{ox}$, $Cr^{3+}_{ox}$, $Co^{8/3+}_{ox}$, $Ni^{2+}_{hy}$, and $Co^{2+}_{hy}$, and it shows stronger protection effect on the γ phase.

Density functional theory↗