Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Al”

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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Al(Ni4Pt)3 by Materials Project

Al(PtNi4)3 is Uranium Silicide-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Pt sites. In the first Pt site, Pt is bonded to twelve Ni atoms to form PtNi12 cuboctahedra that share corners with four equivalent AlNi12 cuboctahedra, corners with eight PtNi12 cuboctahedra, edges with twenty-four NiAl4Ni8 cuboctahedra, a faceface with one AlNi12 cuboctahedra, faces with five PtNi12 cuboctahedra, and faces with twelve NiNi8Pt4 cuboctahedra. There are a spread of Pt–Ni bond distances ranging from 2.56–2.59 Å. In the second Pt site, Pt is bonded to twelve Ni atoms to form PtNi12 cuboctahedra that share corners with twelve PtNi12 cuboctahedra, edges with twenty-four NiNi8Pt4 cuboctahedra, faces with six PtNi12 cuboctahedra, and faces with twelve NiNi8Pt4 cuboctahedra. All Pt–Ni bond lengths are 2.56 Å. There are five inequivalent Ni sites. In the first Ni site, Ni is bonded to eight equivalent Ni and four equivalent Al atoms to form NiAl4Ni8 cuboctahedra that share corners with twelve NiAl4Ni8 cuboctahedra, edges with eight equivalent PtNi12 cuboctahedra, edges with sixteen equivalent NiAl2Ni8Pt2 cuboctahedra, faces with four equivalent AlNi12 cuboctahedra, and faces with fourteen NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.53 Å. All Ni–Al bond lengths are 2.56 Å. In the second Ni site, Ni is bonded to four equivalent Pt and eight Ni atoms to form distorted NiNi8Pt4 cuboctahedra that share corners with twelve NiAl4Ni8 cuboctahedra, edges with four equivalent PtNi12 cuboctahedra, edges with four equivalent AlNi12 cuboctahedra, edges with sixteen NiAl2Ni8Pt2 cuboctahedra, faces with four equivalent PtNi12 cuboctahedra, and faces with fourteen NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.58 Å. In the third Ni site, Ni is bonded to four equivalent Pt and eight equivalent Ni atoms to form NiNi8Pt4 cuboctahedra that share corners with twelve NiNi8Pt4 cuboctahedra, edges with eight equivalent PtNi12 cuboctahedra, edges with sixteen equivalent NiNi8Pt4 cuboctahedra, faces with four equivalent PtNi12 cuboctahedra, and faces with fourteen NiNi8Pt4 cuboctahedra. All Ni–Ni bond lengths are 2.56 Å. In the fourth Ni site, Ni is bonded to two equivalent Pt, eight Ni, and two equivalent Al atoms to form NiAl2Ni8Pt2 cuboctahedra that share corners with twelve NiAl2Ni8Pt2 cuboctahedra, edges with four equivalent PtNi12 cuboctahedra, edges with four equivalent AlNi12 cuboctahedra, edges with sixteen NiAl4Ni8 cuboctahedra, faces with two equivalent PtNi12 cuboctahedra, faces with two equivalent AlNi12 cuboctahedra, and faces with fourteen NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.56 Å. Both Ni–Al bond lengths are 2.53 Å. In the fifth Ni site, Ni is bonded to four Pt and eight Ni atoms to form distorted NiNi8Pt4 cuboctahedra that share corners with twelve NiAl2Ni8Pt2 cuboctahedra, edges with eight PtNi12 cuboctahedra, edges with sixteen NiNi8Pt4 cuboctahedra, faces with four PtNi12 cuboctahedra, and faces with fourteen NiNi8Pt4 cuboctahedra. All Ni–Ni bond lengths are 2.56 Å. Al is bonded to twelve Ni atoms to form AlNi12 cuboctahedra that share corners with four equivalent AlNi12 cuboctahedra, corners with eight equivalent PtNi12 cuboctahedra, edges with twenty-four NiNi8Pt4 cuboctahedra, faces with two equivalent PtNi12 cuboctahedra, faces with four equivalent AlNi12 cuboctahedra, and faces with twelve NiAl4Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al(NO6)3 by Materials Project

AlO8NO3N2O5O2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four hydrogen peroxide molecules, four nitric acid molecules, four nitrogen pentoxide molecules, and four AlO8 clusters. In each AlO8 cluster, Al is bonded in a tetrahedral geometry to four O atoms. There are a spread of Al–O bond distances ranging from 1.72–1.89 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a water-like geometry to two O atoms. There is one shorter (1.24 Å) and one longer (1.61 Å) O–O bond length. In the second O site, O is bonded in a water-like geometry to two O atoms. There is one shorter (1.31 Å) and one longer (1.72 Å) O–O bond length. In the third O site, O is bonded in a distorted water-like geometry to one Al and one O atom. The O–O bond length is 1.31 Å. In the fourth O site, O is bonded in a single-bond geometry to one O atom. In the fifth O site, O is bonded in a distorted single-bond geometry to one Al and one O atom. In the sixth O site, O is bonded in a water-like geometry to two O atoms. In the seventh O site, O is bonded in a single-bond geometry to one Al atom. In the eighth O site, O is bonded in a distorted single-bond geometry to one Al and one O atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Quantifying dislocation density in Al-Cu coatings produced by cold spray deposition

This work quantifies the plastic deformation in terms of dislocation density for a series of cold sprayed Al-Cu coatings with copper contents from 2 mass% to 5 mass%. The success of the deposition and consolidation of the feedstock powders during the cold spray process rely on the occurrence of significant plastic deformation. Inert gas atomized Al-Cu alloy powders were sprayed onto substrates made of an Al-Cu-Mg-Mn alloy (AA2024) to produce dense coatings using a low pressure cold spray system with helium as the carrier gas. X-ray diffraction patterns were obtained from the Al-Cu feedstock powder material and the cold sprayed coatings using a monochromatic X-ray source, and the dislocation density was determined via an X-ray whole profile analysis. Increasing the Cu alloy content (from 2 mass% to 5 mass%) systematically increased the dislocation density in the Al-Cu coatings from (4.3 ± 0.5) × 10 14 m -2 to (7.5 ± 0.8) × 10 14 m -2 . The dislocation densities in the feedstock powders ranging from (0.4 ± 0.1) × 10 14 m -2 to (1.8 ± 0.2) × 10 14 m -2 were all lower than the dislocation densities in the corresponding coatings. The increasing deformation level in the Al-Cu coatings with Cu additions were confirmed by the classic and modified Williamson-Hall analyses of X-ray diffraction data, and peak breadth measurements from neutron diffraction data. Finally, a high density of dislocations was also observed in these coatings via electron backscatter diffraction and transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2025

First-principles elucidation of the effects of Al-doping on Li-ion diffusion in LiCoO 2

Al-doped garnet Li 7 La 3 Zr 2 O 12 solid-electrolyte and LiCoO 2 cathode are promising choices as catholyte materials in all solid-state Li batteries, however, interdiffusion of Al is commonly evident during high-temperature processing and electrochemical cycling. Furthermore, to address the impact of Al interdiffusion on Li + transport properties in LiCoO 2 , we carried out a systematic evaluation of Al doping on Li + diffusion barriers in LiCoO 2 using first-principles based methods. Following the monovacancy diffusion mechanism, Al-doping (primarily at the Co site) is found to improve Li diffusion kinetics in the LiCoO 2 lattice due to favorable CoO 6 octahedral distortion experienced at the transition states. However, when considering the previously established dominant divacancy diffusion mechanism, slower Li diffusion is generally expected. In addition, a broad variation of Li diffusion barriers is observed upon Al doping, which suggests the system may suffer from non-uniform Li incorporation and diffusion that adversely affects its rate capacity during cycling. In summary, this work highlights, for the rational design of catholyte of all solid-state batteries, special attention may need to be paid to address the potential impact of non-intentional doping induced during processing on the overall electrochemical performance of the catholyte.

Al-doped LiCoO2↗
DOE OSTI2021

First-principles calculations for understanding microstructures and mechanical properties of co-sputtered Al alloys

Recent experimental studies show that co-sputtering solutes with Al, together, can refine columnar grain size around few tens of nanometers and promote the formation and enhance the stability of planar defects such as stacking faults (SFs) and grain boundaries (GBs) in Al alloys. These crystal defects and fine columnar grains result in high strength, enhanced strain hardening and thermal stability of Al alloys. Using first-principles density-functional theory (DFT) calculations, we studied the role of eleven solutes in tailoring kinetics and energetics of adatoms and clusters on Al {111} surface, stable and unstable stacking fault energies, and kinetic energy barriers for the migration of defects. The calculations show that most solutes can effectively refine columnar grain size by decreasing the diffusivity of adatoms and surface clusters. These solutes do not necessarily decrease the stacking fault energy of Al alloys, but reduce the formation energy of faulted surface clusters and increase the energy barriers for the recovery of faulted surface clusters. Correspondingly, the formation of SFs is kinetically promoted during sputtering. Furthermore, solutes are segregated into the core of Shockley partial dislocations and play a pinning effect on SFs, SF arrays and twin boundaries, enhancing the thermal stability of these crystal defects. These findings provide insights into the design of high-strength Al alloys for high-temperature applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys

Laser Surface Remelting (LSR) was applied to arc-melted Al-20Si-0.2Sr, Al-20Si-0.2Ce, and Al-20Si hypereutectic alloys to refine microstructures. Experiments revealed that microstructures in the melt pool varied from fully eutectic to a mixture of Al dendrites and inter-dendritic eutectic. We calculated cooling rates using the Eagar-Tsai model and correlated cooling rates with characteristic microstructures, revealing that a cooling rate on the order of 104 K/s could lead to maximized fully eutectic microstructure morphology. Due to rapid solidification, the Si composition in the LSR eutectic was measured at 18.2 wt.%, higher than the equilibrium eutectic composition of 12.6 wt.%Si. Compared to Al-20Si, Ce addition had no significant effect on the volume fraction of the fully eutectic structure but refined Si fibers to approximately 30 nm in diameter. Sr addition did not further refine the diameter of eutectic Si fibers compared to Al-20Si but increased the volume fraction of the fully eutectic microstructure morphology. The refinement ratio (φ) of the Si fiber diameter from the bottom of the melt pool to the surface for the three alloys was similar, at around 28%. The established correlation between the cooling rate and the size and morphology of the microstructure within the melt pool will enable tailoring of the microstructure in laser-processed as well as deposited alloys for high strength and plasticity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Grain Refinement Effect on the Hot-Tearing Resistance of Higher-Temperature Al–Cu–Mn–Zr Alloys

The hot-tearing resistance of Al-Cu-Mn-Zr (ACMZ) alloys was investigated as a step toward introducing these new cast alloys for severe duty, higher-temperature applications, such as cylinder heads for down-sized, turbocharged automotive engines. Alloy Cu compositions were varied from 5 to 8 wt.%. Targeted Ti levels were 0.02, 0.1, and 0.2 wt.% via additions of the Al–5Ti–1B master alloy. Hot-tearing resistance was assessed by visual examination and ranking of the cracking severity in a multi-arm permanent mold casting. It was found that at high impurity contents (Fe and Si of 0.2 wt.% each), the Al–Cu–Mn–Zr alloy with 4.95 wt.% Cu exhibited the poorest hot-tearing resistance, irrespective of the grain refining amount. Microstructural analysis indicated an effective reduction in the grain size, as the Ti additions were increased to 0.02 and 0.1 wt.% Ti via the Al–Ti–B grain refiner. The finest grain size was attained with a 0.1 wt.% Ti. Based on the hot-tearing evaluation, it was found that the additional grain refining via the Al–5Ti–1B master alloy at 0.1 wt.% Ti significantly reduces the hot-tearing susceptibility at Cu contents greater than 7.3 wt.% for ACMZ alloys with low Fe and Si. These findings indicate that the best hot-tearing resistance was observed at a grain refiner level of 0.1 wt.% Ti and high Cu content (greater than 7.3 wt.%). This study to indicates that these Al–Cu–Mn–Zr alloys, which possess excellent microstructural stability and mechanical properties at elevated temperatures, can also possess excellent hot-tearing resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Compositional Modifications to Alter and Suppress Laves Phases in Al x CrMoTa y Ti Alloys

The development of refractory complex concentrated alloys in the Al–Cr–Mo–Ta–Ti alloy system is reported. Alloys with modified Al and Ta concentrations are designed using CALPHAD tools and produced via arc melting and characterized in both as-cast and annealed forms. Properties of the alloys, nature of the microstructures, and phase transformation behavior are described via X-ray diffraction, microstructural characterization, microhardness, and differential scanning calorimetry. Two alloys, namely, Al 0.25 CrMoTa 0.8 Ti and Al 0.75 CrMoTa 0.8 Ti, are represented by a body-centered-cubic matrix phase after annealing, along with a secondary Cr–Ta Laves phase of the C15 and C14 polytypes, respectively. In as-cast and annealed forms, the Al 0.75 CrMoTa 0.45 Ti alloy comprises a single-bcc phase. Microhardness of the Laves phase containing alloys demonstrates susceptibility to cracking, whereas the Al 0.75 CrMoTa 0.45 Ti alloy displays high specific hardness, signs of ductility as evidenced by slip traces near indentations, and minimal scatter of hardness values.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Microstructural Passivation of Patterned Al 2 O 3 Back Contacts on CdS/CdTe Solar Cells

Abstract Patterned aluminum oxide (Al 2 O 3 ) back contact on cadmium telluride (CdTe) solar cells can effectively mitigate the loss of the majority carriers while retaining the passivation benefits for minority carriers. This study investigates the impact of the point‐contact geometry on cell performance, where the spacing of the microholes is systematically varied at a constant microhole diameter (≈16 µm). Microhole arrays are created on an evaporated Al 2 O 3 layer (≈30 nm) on CdTe using laser‐beam lithography and selective wet etching processes. Comparative analysis indicates a significant decrease in fill factor (FF) and short‐circuit current ( I SC ) when the contact fraction falls below 30%, likely due to the Al 2 O 3 barrier impeding majority carriers. Above this fraction, FF and I SC are comparable to those of baseline CdTe cells without Al 2 O 3 . Open‐circuit voltage ( V OC ) shows a gradual decrease as Al 2 O 3 coverage is reduced but exhibits a slight increase (<15 mV) when the contact fraction exceeds 30%. Cathodoluminescence (CL) characterization reveals that significantly improved radiative recombination occurs within the CdTe grain bulk with Al 2 O 3 , whereas this effect on grain boundaries is minimal. The findings imply complex local carrier dynamics in the patterned back‐contact region, closely tied to the microstructural properties of CdTe‐based solar cells.

Roy, Etee Kawna↗
DOE OSTI2024

Electronic Properties of Ultra‐Wide Bandgap B x Al 1− x N Computed from First‐Principles Simulations

Abstract Ultra‐wide bandgap (UWBG) materials such as AlN and BN hold great promise for future power electronics due to their exceptional properties. They exhibit large bandgaps, high breakdown fields, high thermal conductivity, and high mechanical strengths. AlN and BN have been extensively researched, however, their alloys, B x Al 1− x N, are much less studied despite their ability to offer tunable properties by adjusting x . In this article, the electronic properties of 17 recently predicted ground states of B x Al 1− x N in the x = 0 − 1 range are predicted using first‐principles density functional theory and many‐body perturbation theory within GW approximation. All the B x Al 1− x N structures are found to be UWBG materials and have bandgaps that vary linearly from that of wurtzite‐phase ( w ) AlN (6.19 eV) to that of w ‐BN (7.47 eV). The bandstructures of B x Al 1− x N show that a direct‐to‐indirect bandgap crossover occurs near x = 0.25. Furthermore, it is found that B x Al 1− x N alloys have much larger dielectric constants than the constituent bulk materials (AlN = 9.3 ɛ 0 or BN = 7.3 ɛ 0 ), with values reaching as high as 12.1 ɛ 0 . These alloys are found to exhibit large dielectric breakdown fields in the range 9–35 MV cm −1 with a linear dependence on x . This work provides the much needed advancement in the understanding of the properties of B x Al 1− x N to aid their application in next‐generation devices.

Milne, Cody L.↗
DOE OSTI2021

Sub-Microsecond Polarization Switching in (Al,Sc)N Ferroelectric Capacitors Grown on Complementary Metal-Oxide-Semiconductor-Compatible Aluminum Electrodes

In this work, the frequency-dependent ferroelectric properties of 45 nm (Al,Sc)N films sputter deposited on complementary metal–oxide–semiconductor (CMOS)-compatible Al metal electrodes are measured and compared. Low in-plane compressive stress (-10 ± 20 MPa) is observed in (Al,Sc)N thin films deposited on Al electrodes. The (Al,Sc)N films exhibit an imprint in the measured coercive fields (E c ) of -4.3/+5.3 MV cm -1 at 10 kHz. Using positive-up negative-down (PUND) measurements, ferroelectric switching is observed within ≈200 ns of an applied voltage pulse, which demonstrates the ability of ferroelectric (Al,Sc)N to achieve the fast read/write speeds desired in memory devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Phase Selection During Solidification and Solid-State Phase Transformations in an Al-10Ce-8Mn (wt pct) Alloy

In multicomponent Al-Ce alloys, and especially after additive manufacturing (AM), complex and metastable solidification microstructures are frequently observed. Here, in this research, the relationship between solidification conditions and phase selection are explored for an Al-10Ce-8Mn (wt pct) alloy using a systematic study of laser melting conditions. Three solidification modes were observed: primary Al 10 Mn 2 Ce; primary Al 20 Mn 2 Ce; and eutectic FCC Al + Al 20 Mn 2 Ce. These solidification modes were correlated to specific liquid-solid interface velocities using a simple thermal model, showing the change in primary solidification phase for low (< 6.8 × 10 −4 m/s), moderate (between 8.2 × 10 −4 and 5.9 × 10 −2 m/s) and high solidification velocities (> 6.2 x 10 −2 m/s) for the above three solidification microstructures, respectively. These results were rationalized by using interface response function (IRF) theory to describe the solidification undercooling for the possible primary intermetallic phases. The implication of the local phase selection from differing solidification conditions is summarized by a comparison of hardness which demonstrates the potential variance of Vickers hardness from 101 to 242 (VHV) by changing the laser velocity from 1 to 83 mm/s. Interestingly, on heat treatment at 400°C, the decomposition pathways of the solidification microstructure and hardness were also found to be different, thereby opening multiple pathways for spatial microstructure and property control within AM components.

Sisco, Kevin↗
DOE OSTI2021

Deciphering the non-linear impact of Al on chemical durability of silicate glass

The role of Al in aluminosilicate glasses remains somewhat a mystery: at low concentrations, it increases the resistance to hydrolysis of the glass, whereas at high concentrations an opposite effect is observed. To understand the origin of the phenomenon on a fundamental atomistic scale, we performed 577 MD simulations and applied potential mean force (PMF) calculations to estimate the activation barriers for hydrolysis and to statistically correlate them with local structural features of the glass. Models of pure silicate and aluminosilicate glasses are constructed and investigated. PMF simulation results are further validated by the experimental measurements and revealed that Al is very easy to dissociate, but it also increases the glass chemical durability through significantly increasing both the strength of Si and network connectivity of the glass. In contrast, at high Al concentration, preferential dissolution of Al weakens the silicate network, which it supposes to strengthen, and so the glass resistance becomes poor. Through PMF calculations, we evaluated the activation barriers for dissociating bonds around Al as 0.49 eV, which is less than a half of the energy to dissociate bonds around Si in pure silicate (1.22 eV) and around Si in aluminosilicate glass (1.34 eV), all these energy differences being statistically significant. Molecular structural level investigation revealed that Si with Al as a second neighbor in the glass network has a significantly higher activation energy for dissociation than Si in pure silicate glass. Furthermore, the proposed approach opens the way to the development of quantitative predictive models of glass durability.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effect of Al on the formation and structure of alkali-silica reaction products

The use of Al-rich supplementary cementitious materials can effectively reduce the expansion of concrete caused by alkali-silica reaction (ASR). However, the role of Al in mitigating the formation and structure of ASR products is only poorly understood, since direct investigation of the reaction in the micro-scale veins of aggregates is difficult. Recent successful synthesis of ASR products provides a unique opportunity to directly assess the role of Al in ASR. In this study, the effect of Al on the formation and structure of ASR products synthesized at 40 and 80 °C is investigated. It is found that the presence of Al in concentration lower than 0.1 mM neither prevents ASR nor alters the structure of the crystalline ASR products formed at 40 °C. However, formation of the crystalline ASR product at 80 °C is lowered at higher Al content due to the formation of a zeolitic precursor.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Determine the coordination of Al and Si of Fe-rich fly ash: The challenge in NMR and how we probe its heterogeneity using X-ray spectromicroscopy

Scanning transmission X-ray microscopy (STXM) coupled with ptychographic imaging at Al and Si K-edge is a new probe to the microscale chemistry of heterogenous materials. Here, the combined techniques are applied to study local coordination environment of Fe-rich fly ash (FA). Ptychographic imaging at Al K- and Si K-edge highlights the fine Al- and Si-rich morphological features, respectively, at 6 nm pixel resolution. STXM visualizes the inter- and intra-particle variations in the silicate polymerization degree and two types of Al coordination environment in FA. The Si K-edge of SiO4 connected with four-fold coordinated Al is higher than SiO4 sharing oxygen with six-fold coordinated Al. The result is consistent with bulk nuclear magnetic resonance spectroscopy measurement of the Fe-rich sample which, however, is sensitive to paramagnetic Fe and time-consuming. Here, we demonstrate that the combined method has great potential in the studies of chemically heterogenous aluminosilicates.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2022

Effect of aluminum on the FeCr(Al) alloy oxidation resistance in steam environment at low temperature (400 °C) and high temperature (1200 °C)

The effect of aluminum in the FeCr(Al) alloys on the corrosion behavior was studied at two temperatures (400 °C and 1200 °C). For the Fe-21Cr alloy, Cr 2 O 3 layer was formed upon exposure to both temperatures. The addition of Al altered the corrosion mechanism of the alloy. At 1200 °C, a thin α-Al 2 O 3 is formed on the Fe-21Cr-5.5Al alloy. Whereas, at low temperature, a continuous Cr 2 O 3 is formed at the top with an internal Al 2 O 3 layer. These results show that FeCrAl alloys hold promise as Fuel Cladding Materials with Al playing a crucial role under operational as well as accident-like conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Interfacial Void Formation and Self-Healing in Oxide Scales on Al-containing High-Entropy Alloy

The exceptional high-temperature oxidation resistance of Al-containing high-entropy alloys (HEAs) is often attributed to the formation of a protective α-Al 2 O 3 scale. However, the dynamic, atomic-scale mechanisms governing the stability of this scale—including interfacial void formation and the often-postulated but rarely visualized “self-healing” capacity—remain poorly understood. Herein, we reveal the complex evolution of the triple-layer oxide scale on an Al 10 CoCrFeNi HEA through combined electron microscopy and diffraction study. We show that interfacial voids are an inherent consequence of the scaling process, originating from two distinct mechanisms: the Kirkendall effect at the interface between the γ-Al 2 O 3 /α-Al 2 O 3 and alloy driven by cationic diffusion imbalance and volumetric contraction due to phase transformations at the spinel/Cr 2 O 3 interface. Crucially, we provide microstructural evidence consistent with an intrinsic self-healing response. This process is driven by coupled inward diffusion of oxygen and outward diffusion of metal cations, leading to the in-situ formation of transient θ-Al 2 O 3 and spinel phases that partially fill and seal the voids. Here, these results provide atomic-scale insights into the phase evolution, defect formation, and self-repair of oxide scales in HEAs—highlighting pathways to enhance their oxidation resistance in extreme environments.

High-entropy alloy↗
DOE OSTI2024

Effect of microalloying additions on microstructural evolution and thermal stability in cast Al-Ni alloys

Enhancement of thermal stability in Al-Ni alloys through microalloying with slow-diffusing elements, specifically Zr, has been previously reported which is attributed to Zr segregation at the Al/Al 3 Ni interface. In this study, we explore the influence of microalloying Al-Ni alloys with Zr, Ti, V, and Fe on microstructural evolution, hardness, and electrical and thermal conductivity across a range of heat-treatment temperatures from 300 to 450 °C. The distribution of microalloying elements and precipitates after heat treatment is characterized using atom probe tomography (APT). Our investigation confirms Zr segregation to the Al/Al 3 Ni interface, while similar interfacial segregation is absent with the addition of Ti, V, and Fe. Additionally, our analysis of the Al 3 Ni microfiber morphology reveals that their coarsening and spheroidization rates are similar with and without interfacial segregation; thus, retaining the fiber reinforcement through interfacial segregation of slow diffusing elements may not be an effective strategy. Precipitation of L1 2 nanoparticles was found to be the dominant mechanism affecting enhanced hardness and electrical conductivity in Al-Ni-Zr alloys, attributed to precipitation strengthening and solute depletion, respectively. Similar precipitation was not observed for additions of Ti, V, and Fe following heat treatment. We provide a thermodynamic explanation for this limitation. Furthermore, the findings of this study suggest that an effective approach for designing Al-Ni alloys should involve prioritizing microalloying elements to maximize L1 2 precipitation and minimize solute content in the FCC-Al matrix post heat treatment, rather than focusing on Al/Al3Ni interfacial segregation.

36 MATERIALS SCIENCE↗