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DOE OSTI2025

Synthesis and Physical Properties of Manganese Chromium Nitride Thin Films Grown via Molecular Beam Epitaxy

Here, we demonstrate the ability to grow epitaxial thin films of manganese–chromium nitride (Mn x Cr 1–x N) across the entire composition range on magnesium oxide (MgO) (1 0 0) surfaces by molecular beam epitaxy. By independently controlling the ratio of the atomic fluxes of manganese and chromium, the compositional dependence of structural and electrical transport properties is determined. Soft X-ray absorption shows that the valence states of Cr( 3+ ) and Mn( 3+ ) remain identical among these MnCrN epitaxial films. The metallic transport behavior of binary manganese nitride (MnN) and chromium nitride (CrN) is suppressed in the ternary alloys. Changes in room temperature electrical resistivity of up to 100 times and 5 orders of magnitude at cryogenic temperatures are observed. This work expands the variety of nitride compounds available for epitaxial integration and could provide additional flexibility for the development of metal–semiconductor–insulator junctions for spintronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2006

Observations Of A Cast Cu-Cr-Zr Alloy

The calculated phase diagram and observations of Zeng et al were confirmed. 1) Additional X-ray diffraction peaks for aged sample indicates possibility that additional metastable phases may form; 2) Cu5Zr was observed rather than the Cu9Zr2 proposed for the binary Cu-Zr phase diagram. Despite similarities between Zr and Nb, Cu-Cr-Zr does not appear to be a good candidate alloy system for rocket engine applications.

Ellis, David L.↗

NASA NTRS1975

Directionally solidified pseudo-binary eutectics of Ni-Cr-(Hf, Zr)

A pseudo-binary eutectic, in which the intermetallic Ni7Hf2 reinforces the Ni-Cr solid solution phase, was previously predicted in the Ni-Cr-Hf system by a computer analysis. The experimental determination of pseudo binary eutectic compositions and the directional solidification of the Ni-Cr-Hf, Zr, and Ni-Cr-Zr eutectic alloys are discussed. To determine unknown eutectics, chemical analyses were made of material bled from near eutectic ingots during incipient melting. Nominal compositions in weight percent of Ni-18.6Cr-24.0HF, Ni19.6Cr-12.8Zr-2.8Hf, and Ni-19.2Cr-14.8Zr formed aligned pseudo-binary eutectic structures. The melting points were about 1270 C. The reinforcing intermetallic phases were identified as noncubic (Ni,Cr)7Hf2 and (Ni,Cr)7(Hf,Zr)2, and face centered cubic (Ni,Cr)5Zr. The volume fraction of the reinforcing phases were about 0.5.

Kim, Y. G.↗

DOE OSTI2025

Design of novel refractory equiatomic multi-principal elemental alloys based on Mo-Nb-Ti system for Gen IV reactor applications

Excellent irradiation damage resistance demonstrated by multi-principal elemental alloys (MPEAs) has sparked significant interest among researchers, prompting exploration into their vast compositional space, to validate their suitability for nuclear applications. A combined approach of thermodynamic and empirical parameters calculations alongside CALPHAD (CALculation of PHAse Diagrams) for phase formation predictions enable high-throughput material selection for sophisticated applications like nuclear, overcoming laborious and time-consuming experiments. Key thermodynamic and empirical parameters for eight novel equiatomic MPEAs, based on seven low thermal neutron cross section refractory elements, for predicting phase formation were calculated, and equilibrium and non-equilibrium simulations in CALPHAD were employed to comprehensively model the systems. Pseudo binary phase diagram simulations showed that Zr, V or equiatomic CrV additions to the base MoNbTi alloy (MoNbTi-Zr, MoNbTi-V and MoNbTi-CrV alloys) favor the formation of isomorphous body-centered cubic (BCC) phase at high temperatures, while Cr, Al, equiatomic ZrV, or equiatomic CrAl additions (MoNbTi-Cr, MoNbTi-Al, MoNbTi-ZrV or MoNbTi-CrAl alloys) limit the solubility of them. Equilibrium CALPHAD simulations at 750 oC were consistent with XRD results on MoNbTi, MoNbTiZr and MoNbTiCr alloys, and partially for others. Notably, elemental segregation observed in the backscattered electron (BSE) scanning electron microscopy (SEM) images of the alloys was accurately simulated through non-equilibrium Scheil solidification calculations in CALPHAD, further verified by experiments. The precipitation of TiCr2 Laves phase in Cr containing MoNbTiCr and MoNbTiCrAl was accurately predicted while discrepancies were noted in MoNbTiCrV. The equilibrium simulations also provided insights into phase compositions at specific temperatures offering a pathway for tailoring the desired microstructure and properties of these systems. Empirical parameters calculations successfully predicted random solid solution in the base MoNbTi alloy, and with an exception in MoNbTiV and MoNbTiAl, predicted intermetallic precipitation in the rest, especially, Laves phase precipitation in Cr containing alloys.

36 - MATERIALS SCIENCE↗

DOE OSTI2021

Atomic Structure Evolution of Pt–Co Binary Catalysts: Single Metal Sites versus Intermetallic Nanocrystals

Due to their exceptional catalytic properties for the oxygen reduction reaction (ORR) and other crucial electrochemical reactions, PtCo intermetallic nanoparticle (NP) and single atomic (SA) Pt metal site catalysts have received considerable attention. However, their formation mechanisms at the atomic level during high-temperature annealing processes remain elusive. Furthermore, the thermally driven structure evolution of Pt–Co binary catalyst systems is investigated using advanced in situ electron microscopy, including PtCo intermetallic alloys and single Pt/Co metal sites. The pre-doping of CoN 4 sites in carbon supports and the initial Pt NP sizes play essential roles in forming either Pt 3 Co intermetallics or single Pt/Co metal sites. Importantly, the initial Pt NP loadings against the carbon support are critical to whether alloying to L1 2 -ordered Pt 3 Co NPs or atomizing to SA Pt sites at high temperatures. High Pt NP loadings (e.g., 20%) tend to lead to the formation of highly ordered Pt 3 Co intermetallic NPs with excellent activity and enhanced stability toward the ORR. In contrast, at a relatively low Pt loading (<6 wt%), the formation of single Pt sites in the form of PtC 3 N is thermodynamically favorable, in which a synergy between the PtC 3 N and the CoN 4 sites could enhance the catalytic activity for the ORR, but showing insufficient stability.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Microstructure evolution in U-10Zr alloy irradiated by swift Xe ions at 700 °C

The post-irradiation examination (PIE) results of U-10Zr binary metallic fuel that was irradiated by 84 MeV Xe ions at 700 °C are reported here. The U-10Zr specimen was synthesized by homogenizing elemental U and Zr powders through arc-melting. The as-fabricated U-10Zr was dominated by the sub-micron acicular α+ δ phase. After being irradiated by 84 MeV Xe ions at 700 °C up to 2.19 ×10 17 ions/cm 2 fluence, the U-10Zr was speculated to evolve into micro-scale γ 1 + γ 2 phases as predicted by the U-Zr phase diagram. During post-irradiation cooling, the U-rich γ 1 phase was mainly transformed to the αphase, while the Zr-rich γ 2 phase was partially retained along with formation of hexagonal structure phase (δ or ω). Xe bubbles formed in the γ 1 and γ 2 phases have salient different morphologies, implying faster Xe diffusion in the γ 1 phase than the γ 2 phase. The quantitative bubble morphology data collected in this study can provide valuable references for the development and validation of fuel performance models for this fuel.

36 MATERIALS SCIENCE↗

NASA NTRS1973

Some possible filler alloys with low vapor pressures for refractory-metal brazing

A compilation of eutectics and melting-point minima for binary combinations of metals having vapor pressures below 10 to the minus 10th power torr at 1500 degrees K and .00005 torr at 2000 degree K is presented. These compositions and others near them on their phase diagrams are potential special brazing fillers for refractory metals. Some possible problems and advantages for fusion bonds of such mixtures are indicated. Evaluations of brazing fillers containing refractory metals are reported.

Morris, J. F.↗

DOE OSTI2022

Intergranular oxidation and oxygen transport in Ni-20Cr during exposure to model dry and wet oxidation environments

Selective oxidation is a critical component of the proposed internal oxidation mechanism of stress corrosion cracking (SCC) for Ni-based alloys in primary water reactor (PWR) operation. To isolate and study this process, the binary Ni-20Cr was exposed to pressurized water and a CO/CO2 gas mixture. In both environments, the oxygen potential was kept under the Ni/NiO line to stimulate penetrative intergranular attack. A combination of electron microscopy and atom probe tomography was used to study the nanometer-scale details of the passivation and penetrative intergranular oxidation processes at high-energy grain boundaries. Oxygen transport towards the terminating oxidation front is elucidated with dedicated usage of oxygen isotopic tracer exchange experiments to support classical theories of internal oxidation, revealing preferred oxygen transport paths were visualized with sub-nanometer resolution.

Weiser, Martin↗

NASA NTRS1975

Directionally solidified pseudo-binary eutectics of Ni-Cr-/Hf,Zr/

This report is concerned with the experimental determination of pseudo binary eutectic compositions and the directional solidification of the Ni-Cr-Hf,Zr, and Ni-Cr-Zr eutectic alloys. To determine unknown eutectics, chemical analyses were made of material bled from near eutectic ingots during incipient melting. Nominal compositions in weight per cent of Ni-18.6Cr-24.0Hf, Ni-19.6Cr-12.8Zr-2.8Hf, and Ni-19.2Cr-14.8Zr formed aligned pseudo-binary eutectic structures. The melting points were about 1270 C. The reinforcing intermetallic phases were identified as noncubic (Ni,Cr)7Hf2 and (Ni,Cr)7(Hf,Zr)2, and face centered cubic (Ni,Cr)5Zr. The volume fraction of the reinforcing phases were about 0.5.

Kim, Y. G.↗

NASA NTRS1978

Some properties of low-vapor-pressure braze alloys for thermionic converters

Density, dc electrical resistivity, thermal conductivity, and linear thermal expansion are measured for arc-melted rod-shaped samples of binary eutectics of Zr, Hf, Ru, Nb, Ir, Mo, Ta, Os, Re, and W selected as very-low-pressure braze fillers for thermionic converters. The first two properties are measured at 296 K for Zr-21.7 at% Ru, Zr-13 wt% W, Zr-19 wt% W, Zr-22.3 at% Nb, Nb-66.9 at% Ru, Hf-25.3 wt% Re, Zr-25.7 at% Ta, Hf-22.5 at% W, and Nb-35 wt% Mo. The last property is measured from 293 K to 2/3 melting point for specified alloys of different compositions. Resistivities of 0.000055 to 0.000181 ohm-cm are observed with the alloys having resistivities about ten times that of the less resistive constituent metal and about three times that of the more resistive constituent metal, except for Zr-19 wt% W and Nb-35 wt% Mo (greater resistivities). Thermal expansion coefficients vary from 0.000006 to 0.0000105/K. All brazes exhibit linear thermal expansion near that of their constituent metals.

Bair, V. L.↗

DOE OSTI2022

Transformation of a ceramic precursor to a biomedical (metallic) alloy: Part I – sinterability of Ta 2 O 5 and TiO 2 mixed oxides

Mixed Ta 2 O 5 – TiO 2 binary system was studied by a combination of differential thermal analysis (DTA), scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and in situ high temperature X-ray diffraction (HT-XRD) techniques. Different compositions of the mixed oxide powders were fabricated by ball–milling the powdered compositions, pelletizing the homogenized composite powders, and heating the green pellets in air at different temperatures for fixed time intervals. The sintered pellets were evaluated and characterized with respect to porosity, morphology, and phase distribution. DTA runs of the un-sintered powders indicated the onset temperatures for both exothermic and endothermic changes in the binary system. Significant amount of sintering was observed to take place at temperatures higher than 900 °C. Both room and high temperature X-ray diffraction patterns exhibited consistency in phase formation. A ternary compound (TaTiO 4 ) and a ternary solid solution (Ti 0.33 Ta 0.67 O 2 ) were observed to form in both room and high temperatures in addition to the respective binary phases (Ta 2 O 5 and TiO 2 ). A sintering temperature in the range 900–1000 °C was observed to be adequate to achieve the requisite mechanical strength and optimum internal porosity (40–48%) for subsequent electrochemical polarization experiments.

36 MATERIALS SCIENCE↗

DOE OSTI2022

High-temperature superelasticity in NiTiPt and NiTiPd shape memory alloys

Alloying NiTi shape memory alloys with sufficient Pt and Pd at the expense of Ni has been shown to increase transformation temperatures well above those possible with the binary composition, enabling consideration of a new class of high-temperature mechanical sensors and actuators. To achieve shape memory behavior at temperatures greater than 200 °C, previous studies of NiTiPt and NiTiPd compositions have focused primarily on alloys with greater than 16 at.% Pt and 25 at.% Pd. While generally not the focus, none of these previous studies demonstrated superelastic behavior at high temperatures. In an effort to identify alloys that transform to austenite at approximately 200 °C and exhibit superelastic behavior with recoverable strains greater than 2%, a series of Ti-rich NiTiPt ternary alloys with 15.5–16.5 at.% Pt, and Ti-rich NiTiPd ternary alloys with 25–26 at.% Pd have been targeted. The polycrystalline alloys were processed via arc melting followed by homogenization heat treatment. Thermomechanical properties were measured using electro-discharge machined tension test coupons and a miniature load frame equipped with a clamshell furnace. Ultimately, superelasticity in uniaxial tension with clear plateau regions was demonstrated and characterized in these alloys at temperatures between 219 °C and 270 °C.

Massad, Jordan E.↗

DOE OSTI2023

Resolving Atomic-Scale Structure and Chemical Coordination in High-Entropy Alloy Electrocatalysts for Structure–Function Relationship Elucidation

The recent breakthrough in confining five or more atomic species in nanocatalysts, referred to as high-entropy alloy nanocatalysts (HEAs), has revealed the possibilities of multielemental interactions that can surpass the limitations of binary and ternary electrocatalysts. The wide range of potential surface configurations in HEAs, however, presents a significant challenge in resolving active structural motifs, preventing the establishment of structure-function relationships for rational catalyst design and optimization. Here, we present a methodology for creating sub-5 nm HEAs using an aqueous-based peptide-directed route. Using a combination of pair distribution function and X-ray absorption spectroscopy, HEA structure models are constructed from reverse Monte Carlo modeling of experimental data sets and showcase a clear peptide-induced influence on atomic-structure and chemical miscibility. Coordination analysis of our structure models facilitated the construction of structure-function correlations applied to electrochemical methanol oxidation reactions, revealing the complex interplay between multiple metals that leads to improved catalytic properties. Our results showcase a viable strategy for elucidating structure-function relationships in HEAs, prospectively providing a pathway for future materials design.

36 MATERIALS SCIENCE↗

NASA NTRS2013

Empirical Study of the Multiaxial, Thermomechanical Behavior of NiTiHf Shape Memory Alloys

An empirical study was conducted to characterize the multiaxial, thermomechanical responses of new high temperature NiTiHf alloys. The experimentation included loading thin walled tube Ni(sub 50.3)Ti(sub 29.7)Hf(sub 20) alloy samples along both proportional and nonproportional axial-torsion paths at different temperatures while measuring surface strains using stereo digital image correlation. A Ni(sub 50.3)Ti(sub 33.7)Hf(sub 16) alloy was also studied in tension and compression to document the effect of slightly depleting the Hf content on the constitutive responses of NiTiHf alloys. Samples of both alloys were made from nearly texture free polycrystalline material processed by hot extrusion. Analysis of the data shows that very small changes in composition significantly alter NiTiHf alloy properties, as the austenite finish (Af) temperature of the 16-at Hf alloy was found to be approximately 60 C less than the 20-at Hf alloy (approximately 120 C vs. 180 C). In addition, the 16-at Hf alloy exhibited smaller compressive transformation strains (2 vs. 2.5 percent). Multi-axial characterization of the 20-at % Hf alloy showed that while the random polycrystal transformation strains in tension (4 percent) and compression (2.5 percent) are modest in comparison with binary NiTi (6 percent, 4 percent), the torsion performance is superior (7 vs. 4 shear strain width to the pseudoelastic plateau).

tensile deformation↗

DOE OSTI2026

From binary to quinary: The rationale and development of GaInAsSbBi for mid- and long-wave infrared sensing applications

Given the added complexity in flux calibration and composition evaluation inherent to quinary alloy growth, what motivates compounding the challenges of III–V-Bi growth with the goal of producing a quinary alloy of GaInAsSbBi for mid- and long-wave infrared sensing applications? Each elemental constituent provides some additional design freedom to achieve the ultimate goal of producing a lattice-matched, bulk random alloy mid-wave infrared III–V material with smooth surface morphology and high optoelectronic quality to enable high performance elevated operating temperatures. Here, this paper reviews the evolution of Bi-containing semiconductor research, focusing on mid- and long-wave infrared materials and highlighting key research findings that motivated the decisions to accept the added complexity in going from binaries like InAs or InSb, to InAsBi, to InAsSbBi, and, finally, to GaInAsSbBi to meet the performance demands of advanced infrared sensing applications.

Webster, Preston T. [Air Force Research Laboratory↗

DOE OSTI2020

Oxidation behavior of Fe-Cr-2Si alloys in high temperature steam

FeCrSi alloys have been proposed as alternatives to FeCrAl alloys for accident-tolerant fuel cladding in light water reactors. Experiments on the oxidation resistance of three Fe-Cr-2Si alloys in high-temperature steam, with 12, 16, and 20 wt. % Cr, show that ≥16 % Cr is sufficient to form a thin, passivating, binary oxide layer. Additionally, at 1200 °C, only Cr 2 O 3 and SiO 2 form on Fe 16 Cr 2 Si and Fe 20 Cr 2 Si, while additional ternary Fe oxides form on Fe 12 Cr 2 Si. Decohesion and spalling of oxide were observed on Fe-Cr-Si alloys exposed to steam at 900 °C and above. Fe 20 Cr 2 Si exhibits the best oxidation resistance of the three in high-temperature steam.

36 MATERIALS SCIENCE↗

NASA NTRS1992

Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transformation temperature

One of the ongoing challenges of the aerospace industry is to develop more efficient turbine engines. Greater efficiency entails reduced specific strength and larger temperature gradients, the latter of which means higher operating temperatures and increased thermal conductivity. Continued development of nickel-based superalloys has provided steady increases in engine efficiency and the limits of superalloys have probably not been realized. However, other material systems are under intense investigation for possible use in high temperature engines. Ceramic, intermetallic, and various composite systems are being explored in an effort to exploit the much higher melting temperatures of these systems. NiAl is considered a potential alternative to conventional superalloys due to its excellent oxidation resistance, low density, and high melting temperature. The fact that NiAl is the most common coating for current superalloy turbine blades is a tribute to its oxidation resistance. Its density is one-third that of typical superalloys and in most temperature ranges its thermal conductivity is twice that of common superalloys. Despite these many advantages, NiAl requires more investigation before it is ready to be used in engines. Binary NiAl in general has poor high-temperature strength and low-temperature ductility. On-going research in alloy design continues to make improvements in the high-temperature strength of NiAl. The factors controlling low temperature ductility have been identified in the last few years. Small, but reproducible ductility can now be achieved at room temperature through careful control of chemical purity and processing. But the mechanisms controlling the transition from brittle to ductile behavior are not fully understood. Research in the area of fatigue deformation can aid the development of the NiAl system in two ways. Fatigue properties must be documented and optimized before NiAl can be applied to engineering systems. More importantly though, probing the deformation mechanisms operating in fatigue will lead to a better understanding of NiAl's unique characteristics. Low cycle fatigue properties have been reported on binary NiAl in the past year, yet those studies were limited to two temperature ranges: room temperature and near 1000 K. Eventually, fatigue property data will be needed for a wide range of temperatures and compositions. The intermediate temperature range near the brittle-to-ductile transition was chosen for this study to ascertain whether the sharp change occurring in monotonic behavior also occurs under cyclic conditions. An effort was made to characterize the dislocation structures which evolved during fatigue testing and comment on their role in the deformation process.

Antolovich, Stephen D.↗

NASA NTRS2003

Alloy Design Data Generated for B2-Ordered Compounds

Developing alloys based on ordered compounds is significantly more complicated than developing designs based on disordered materials. In ordered compounds, the major constituent elements reside on particular sublattices. Therefore, the addition of a ternary element to a binary-ordered compound is complicated by the manner in which the ternary addition is made (at the expense of which binary component). When ternary additions are substituted for the wrong constituent, the physical and mechanical properties usually degrade. In some cases the resulting degradation in properties can be quite severe. For example, adding alloying additions to NiAl in the wrong combination (i.e., alloying additions that prefer the Al sublattice but are added at the expense of Ni) will severely embrittle the alloy to the point that it can literally fall apart during processing on cooling from the molten state. Consequently, alloying additions that strongly prefer one sublattice over another should always be added at the expense of that component during alloy development. Elements that have a very weak preference for a sublattice can usually be safely added at the expense of either element and will accommodate any deviation from stoichiometry by filling in for the deficient component. Unfortunately, this type of information is not known beforehand for most ordered systems. Therefore, a computational survey study, using a recently developed quantum approximate method, was undertaken at the NASA Glenn Research Center to determine the preferred site occupancy of ternary alloying additions to 12 different B2-ordered compounds including NiAl, FeAl, CoAl, CoFe, CoHf, CoTi, FeTi, RuAl, RuSi, RuHf, RuTi, and RuZr. Some of these compounds are potential high temperature structural alloys; others are used in thin-film magnetic and other electronic applications. The results are summarized. The italicized elements represent the previous sum total alloying information known and verify the computational method used to establish the table. Details of the computational procedures used to determine the preferred site occupancy can be found in reference 2. As further substantiation of the validity of the technique, and its extension to even more complicated systems, it was applied to two simultaneous alloying additions in an ordered alloy.

Noebe, Ronald D.↗