A thermodynamic assessment of the Pu-Ni system has been performed using the CALPHAD (CALculation of PHAse Diagrams) method, leveraging both experimentally available data for phase equilibria and new density functional theory (DFT) calculations for heat of formation and heat capacity predictions. Heat of formation for the PuNi, PuNi2, PuNi3, PuNi4, PuNi5, and Pu2Ni17 intermetallic compounds have been calculated using three different DFT methods and compared to the final CALPHAD assessment. In this work, we include an extensive review of the experimental data to optimize Gibbs energy parameters for the CALPHAD fit. In addition, this work leverages DFT computed heat capacity for the PuNi intermetallic to better assess the Pu-rich portion of the phase diagram. This work highlights the overall lack of experimental data and uncertainty in determined phase boundaries for this system but provides the first thermodynamic assessment of the Pu-Ni binary system grounded by rigorous DFT calculations.

The composition Al-16Ce-1Mg has been developed as a dedicated alloy for processing by laser powder bed fusion (LPBF). Guided by thermodynamic considerations and exploiting the unique conditions during LPBF, the strongly hypereutectic alloy features nm-scale aluminum dendrites reinforced by a continuous intermetallic network. The unique temperature stability of Al-Ce alloys as well as the microstructure topology and scale grant the alloy high strength in as-printed state with excellent thermal stability. The superior mechanical properties of the continuously reinforced nanocomposite were established by comparison with the spheroidized, microstructure of similar scale.

Uranium carbides with refractory metal additions are considered for Gen IV nuclear reactors and nuclear thermal propulsion as fuels for their high-temperature and corrosion resistant properties. Understanding kinetic effects that dictate microstructural evolution during fabrication and operating conditions is essential to advance technological development of these fuels. This work presents the development of an atomic mobility database for CNb-U systems based off available experimental data supported with ab-initio methods. The mobility assessments and uncertainty quantification (using Markov chain Monte Carlo) were conducted in the Kawin software. Carbon diffusion is considered dominant, as metal diffusion is much slower, with niobium diffusion being even slower and rate limiting than uranium metal. We provide a comprehensive and self-consistent thermo-kinetic database that is validated by diffusion couple simulations through Kawin. This enables prediction of microstructural and phase evolution critical for the development and lifetime assessment of next generation nuclear fuels.

The production of ceramics from uranium coordination compounds can be achieved through thermal processing if an excess amount of the desired atoms (i.e., C or N), or reactive gaseous products (e.g., methane or nitrogen oxide) is made available to the reactive uranium metal core via decomposition/fragmentation of the surrounding ligand groups. Here, computational thermodynamic approaches were utilized to identify the temperatures necessary to produce uranium metal from some starting compounds─UI4(TMEDA)2, UCl4(TMEDA)2, UCl3(pyridine)x, and UI3(pyridine)4. Experimentally, precursors were irradiated by a laser under various gaseous environments (argon, nitrogen, and methane) creating extreme reaction conditions (i.e., fast heating, high temperature profile >2000 °C, and rapid cooling). Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligands yielding uranium ceramics. Residual gas analysis identified vaporized products from the laser irradiation, and the final ceramic products were characterized by powder X-ray diffraction. The composition of the uranium precursor as well as the gaseous environment had a direct impact on the production of the final phases.

Cerium oxide is a low-value byproduct of rare-earth mining yet constitutes the largest fraction of the rare earth elements. The reduction of cerium oxide by liquid aluminum is proposed as an energy- and cost-efficient route to produce high-strength Al-Ce alloys. This work investigated the mechanism of a multi-step reduction reaction to facilitate the industrial adaptation of the process. Differential scanning calorimetry in combination with time-resolved synchrotron diffraction data uncovered the rate-limiting reaction step as the origin of the reported temperature dependence of reduction efficiency. This is the first in situ study of a metallothermic reaction mechanism and will serve as guidance for cost- and energy efficient industrial process control.

Alloys that are Ni-doped, such as the (Sm1−yZry)(Fe1−xCox)12 and (Ce0.5Sm0.5)Fe10Co2 systems, are studied because of their magnetic properties. The (Sm1−yZry)(Fe1−xCox)11−zTiz and (Ce.1−xSmx)Fe9Co2Ti alloys are considered contenders for vastly effective permanent magnets because of their anisotropy field and Curie temperature. Ti can act as a stabilizer for the SmFe12 compound but substantially suppresses saturation magnetization. To maintain the saturation magnetization in the scope of 1.3–1.5 T, we propose substituting a particular quantity of Fe and Co in the (Sm1−yZry)(Fe1−xCox)12 and (Ce0.5Sm0.5)Fe10Co2 alloys with Ni. By performing ab initio calculations, we show that Ni incorporation results in increased thermodynamic stability and, in contrast to Ti, has a parallel spin moment aligned to the moment of the SmFe12 compound and improves its saturation magnetization without affecting the anisotropy field or Curie temperature.

Al-Ce-based alloys are promising candidates for additive manufacturing (AM) due to their hot cracking resistance and because they do not require heat treatment to obtain precipitation strengthening. The rapid solidification characteristic of AM can lead to enhanced mechanical properties; however, the strengthening mechanisms over large composition ranges are unclear. Here, combinatorial synthesis by directed-energy deposition (DED) and hardness measurements were used to rapidly map the composition-dependent strength of the ternary Al-Ce-Mg system. Tensile testing and microstructure characterization of selected compositions were performed to elucidate the compositional dependence of the strengthening mechanisms. Al11Ce3 precipitates were present in all cases, and the maximum hardness (1.25 GPa) was measured for the Al-8Ce-10Mg composition. A combination of (i) Hall-Petch strengthening, based on the FCC matrix phase cell size; (ii) precipitation strengthening, based on Al11Ce3 volume fraction and size; and (iii) solid solution strengthening, based on Mg composition of the matrix phase, were used to account for the measured strengths. Hardness is shown to correlate well with ultimate tensile strength in alloys with substantial work-hardening, highlighting the value of surface-based techniques for rapid screening.

Al-Ce-based alloys are promising candidates for additive manufacturing (AM) due to their hot-cracking resistance and because they do not require heat treatment to obtain precipitation strengthening. Rapid solidification rates enabled by AM methods can lead to enhanced mechanical properties; however, the strengthening mechanisms over large composition ranges were unclear. Here, combinatorial synthesis by directed-energy deposition (DED) and hardness measurements were used to rapidly map the composition-dependent strength of the ternary Al-Ce-Mg system. Tensile testing and microstructure characterization of selected compositions were performed to elucidate the compositional dependence of the strengthening mechanisms. Al11Ce3 precipitates were present in all cases, and the maximum hardness (1.25 GPa) was measured for the Al-8Ce-10Mg composition. A combination of (i) Hall-Petch strengthening, based on the FCC-matrix-phase cell size; (ii) particle strengthening, based on Al11Ce3 volume fraction and size; and (iii) solid-solution strengthening, based on Mg composition of the matrix phase, were used to account for the measured strengths. Vickers hardness is shown to correlate well with ultimate tensile strength in these alloys, highlighting the value of surface-based techniques for rapid screening. (C) 2023 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

We present high-temperature thermodynamic properties for graphite from first-principles anharmonic theory. The ab initio electronic structure is obtained from density-functional theory coupled to a lattice dynamics method that is used to model anharmonic lattice vibrations. This combined approach produces free energies and specific heats for graphite that compare well with available experiments and results from models that empirically represent experimental data, such as CALPHAD. We show that anharmonic theory for the phonons is essential for accurate thermodynamic quantities above about 1000 K.

(Fe1-xGax)92Zr8 amorphous and nanocrystalline alloys with x = 0.15 to x = 0.36 were investigated to improve the magnetic softness of Galfenol-type alloys and to evaluate their magnetostrictive properties. The samples were prepared by melt spinning of arc melted ingots. The rapidly solidified ribbons were annealed at 823 K for 1 h to produce a nanocrystalline structure. X-ray Diffraction data showed that after annealing, bodycentered cubic (BCC) Fe-Ga phase crystallized for x = 0.15 to x = 0.26. When x exceeded 0.26, the ribbons crystallized into BCC and a ternary intermetallic phase (i.e., ZrFe6Ga6) which has deteriorating effect on saturation magnetization, magnetic softness and magnetostriction coefficient. The annealed ribbons' saturation magnetization value decreases from 126 Am2/kg to 54 Am2/kg as the Ga content increased from x = 0.15 to x = 0.36. The alloy with x = 0.26 annealed at 823 K for 1 h shows a peak magnetostriction of 10 ppm with saturation magnetization of 110 Am2/kg and coercivity of 260 A/m. (c) 2023 Elsevier B.V. All rights reserved.

Magnetostrictive iron-aluminum alloys can be a low-cost, mechanically stable alternative to iron-gallium and rare earth-iron alloys. The magnetostrictive performance of polycrystalline Fe-Al (alfenol) with 13-24 at. % Al was investigated, studying the role of compositional variation and thermal history. It was found that rapid cooling enhances the magnetostrictive response, and peak magnetostriction was found in Fe78Al22 by high temperature annealing followed by quenching. Synchrotron diffraction enabled a direct correlation of magnetostrictive behavior and the transition from short-range order to long-range ordered cluster domains in the material which can be suppressed by rapid cooling. Following recent success of doping Fe-Ga with rare earth elements, we investigated the influence of Ce doping on improving magnetostriction and found that Fe-Al shows negligible solubility for cerium, inhibiting potential magnetostriction enhancement. Our results illustrate the complex interplay between phase stability, ordering, and optimized magnetostrictive response.

In a ground-interacting nuclear explosion, elements derived from environmental and anthropogenic material, such as iron, silicon, and aluminum, can be incorporated into the fireball. When significant amounts of metals are entrained, the resulting melt may display immiscible textures. The composition of these textures is a record of the temperature of formation and cooling rates (or thermodynamic stability) of the melts and can provide unique constraints on the early cooling conditions of these events. Here, a thermodynamic approach using calculated phase diagrams, the CALPHAD method, is used to predict temperature and composition ranges where stable liquid immiscibility might result in the textures observed in nuclear fallout glass. Sensitivity of the immiscibility to the presence of relative Al, Ca, and Mg content is also explored and compared to fallout samples, and partition coefficients are introduced to understand the preferred distribution of components into each liquid phase.

Doping of magnetostrictive galfenol (Fe82Ga18, in at. %) with rare-earth elements significantly enhancesmagnetostriction, with the largest gains achieved in textured melt-spun ribbons. Here, it is demonstrated thateven extremely dilute Ce, as little as 65 ppm, can double the magnetostrictive response of galfenol when coupledwith an appropriate heat treatment. This improvement is correlated with a compression of the host lattice, bothof which reach their maximum extent at the calculated solubility limit of Ce in in body-centered cubic (bcc)galfenol, similar to 50 ppm. Beyond this point, excess Ce segregates into CeGa2, which forms an interdendritic networkthroughout the sample at high Ce levels and cannot be resolutionized through heat treatments. These findingspoint to the importance of solubility limits (i.e., equilibrium thermodynamics) in determining appropriate dopinglevels or heat treatment couples to optimize magnetostrictive performance, confirming that overdoping is activelydetrimental to both material properties and cost.

UI4(1,4-dioxane)2 was subjected to laser-based heating─a method that enables localized, fast heating (T > 2000 °C) and rapid cooling under controlled conditions (scan rate, power, atmosphere, etc.)─to understand its thermal decomposition. A predictive computational thermodynamic technique estimated the decomposition temperature of UI4(1,4-dioxane)2 to uranium (U) metal to be 2236 °C, a temperature achievable under laser irradiation. Dictated by the presence of reactive, gaseous byproducts, the thermal decomposition of UI4(1,4-dioxane)2 under furnace conditions up to 600 °C revealed the formation of UO2, UIx, and U(C1-xOx)y, while under laser irradiation, UI4(1,4-dioxane)2 decomposed to UO2, U(C1-xOx)y, UC2-zOz, and UC. Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligand (1,4-dioxane = C4H8O2) instead of producing pure U metal. The results highlight the potential to co-develop uranium precursors with specific irradiation procedures to advance nuclear materials research by finding new pathways to produce uranium carbide.

Ni-doped Sm(Fe1−xCox)12 alloys are investigated for their magnetic properties. The Sm(Fe,Co)11M1 compound (M acts as a stabilizer) with the smallest (7.7 at.%) rare-earth-metal content has been recognized as a possible contender for highly efficient permanent magnets thanks to its significant anisotropy field and Curie temperature. The early transition metals (Ti-Mn) as well as Al, Si, and Ga stabilize the SmFe12 compound but significantly decrease its saturation magnetization. To keep the saturation magnetization in the range of 1.4–1.6 T, we suggest replacing a certain amount of Fe and Co in the Sm(Fe1−xCox)12 alloys with Ni. Ni plays the role of a thermodynamic stabilizer, and contrary to the above-listed elements, has the spin moment aligned parallel to the spin moment of the SmFe12 compound, thereby boosting its saturation magnetization without affecting the anisotropy field or Curie temperature.

The high-temperature thermodynamical properties for the actinide monocarbides and mononitrides ThC, ThN, UC, UN, PuC, and PuN are calculated from first-principles electronic-structure theory. The electronic structure is modeled with density-functional theory (DFT) and is fully relativistic, including the spin-orbit interaction. Furthermore, the DFT is extended to account for orbital–orbital interactions, by means of a parameter-free orbital-polarization (OP) technique, that has proven to be essential for the 5f electrons in plutonium. Strong anharmonicity and the temperature dependence of the lattice vibrations are captured with the self-consistent ab initio lattice dynamics (SCAILD) method. The calculated free energies and heat capacities are compared to published results from quasi-harmonic (QH) theory, and experiments, where available. For the uranium and plutonium compounds, we make use of CALPHAD assessments to help evaluate the theory. Generally, our anharmonic relativistic approach compares well with both CALPHAD and experiments. For the thorium compounds, our theory is in good accord with QH modeling of the free energy at lower temperatures but for the heat capacity the comparison is less favorable.

Laser-induced heating is increasingly being used for rapid material processing. Here, the decomposition pathways of uranium triiodide and ammonium uranium fluoride during laser irradiation are reported. The experimental results are supported by a simplified predictive computational thermodynamics technique that provides estimation of the formation energetics of ammonium uranium fluoride. Results reveal rapid decomposition of material via laser heating with evolution of gaseous reaction products and formation of uranium metal from uranium iodide feedstock and uranium fluoride from ammonium uranium fluoride feedstock, respectively. This information can be exploited for processing of uranium precursors into desirable compounds for nuclear fuel cycle research.