Increasing Al Content Research Articles

Self-propagating high-temperature synthesis of AlxCoCrFeNiMoy high-entropy alloys: thermochemical modelling, microstructural evaluation and high temperature oxidation behaviour

In this study, the feasibility of the synthesis of AlxCoCrFeNiMoy (0.5 < x < 3, y = 0.5,1) alloys via cost and energy efficient thermochemical modelling assisted (FactSage™) aluminothermic self-propagating high-temperature synthesis (SHS) method was investigated. In addition, selected SHS alloys were also suction-casted into a bar shape by using a vacuum arc melter and the microstructural changes and oxidation behaviour of selected alloys were investigated. The characterization results demonstrated that AlxCoCrFeNiMoy (0.5 < x < 3, y = 0.5,1) master alloys can be successfully synthesized via thermochemical modelling assisted SHS method with a substantial composition control. The microstructures of the SHS alloys were found to comprise of the FCC-A1, BCC (A2, B2) and σ phases with varying fractions depending on the composition. Increasing Al content was found to increase the hardness of the alloys from 278 HV to 829 HV for the AlxCoCrFeNiMo0.5 system. For AlxCoCrFeNiMo system, on the other hand, it had an increasing effect from Al0.5 to Al1.0 (from 659 HV to 903 HV) initially and then decreased the hardness to the levels of 773 HV with the further addition of Al. Suction-cast alloys exhibited rather similar microstructures with similar phase constituents and hardness values. As a general trend primer B2 phase fraction was increased due to higher cooling rate. Oxidation studies revealed that the Al3.0Mo0.5 alloy, which has higher B2 content (919 HV), exhibited better oxidation resistance after 100 h of exposure to air at 800 °C. Postulated scaling mechanisms, supported with the CALPHAD simulations and Raman analyses, revealed the formation of non-protective spinel oxides and sublimation of volatile MoOx oxides before the stabilization of a protective M2O3 (M = Al,Cr) layer, especially for the AlCoCrFeNiMo alloy.

Complexation mechanism of Pb2+ on Al-substituted hematite: A modeling study and theoretical calculation

Hematite nanoparticles commonly undergoes isomorphic substitution of Al3+ in nature, while how the Al-substitution-induced morphological change, defective structure and newly generated Al-OH sites affect the adsorption behavior of hematite for contaminants remains poorly understood. Herein, the interfacial reactions between Al-substituted hematite and Pb2+ was investigated via CD-MUSIC modeling and DFT calculations. As the Al content increased from 0% to 9.4%, Al-substitution promoted the proportion of (001) facets and caused Fe vacancies on hematite, which increased the total active site density of hematite from 5.60 to 17.60 sites/nm2. The surface positive charge of hematite significantly increased from 0.096 to 0.418 C/m2 at pH 5.0 due to the increases in site density and proton affinity (logKH) of hematite under Al-substitution. The adsorption amount of hematite for Pb2+ increased from 3.92 to 9.74 mmol/kg at pH 5.0 and 20 μmol/L initial Pb2+ concentration with increasing Al content. More Fe vacancies may lead to a weaker adsorption energy (Ead) of hematite for Pb2+, while the Ead was enhanced at higher Al content. The adsorption affinity (logKPb) of bidentate Pb complexes slightly increased while that of tridentate Pb complexes decreased with increasing Al content due to the presence of ≡AlOH-0.5 and ≡Fe2AlO-0.5 sites. Tridentate Pb complexes were dominant species on the surface of pure hematite, while bidentate ones became more dominant with increasing Al content. The obtained model parameters and molecular scale information are of great importance for better describing and predicting the environmental fate of toxic heavy metals in terrestrial and aquatic environments.

First-principles calculation of phase transitions and mechanical properties of (CoCrNi)100−xAlx (0 ≤ x ≤ 28 at. %) high-entropy alloys

In the two-phase high-entropy alloys (HEAs) (i.e., FCC, BCC), the modulation of the BCC phase is crucial for improving the mechanical properties of FCC-type HEAs. The stability of the phase of (CoCrNi)100−xAlx (0 ≤ x ≤ 28 at. %) HEAs is studied using first-principles calculations. The Al content on the phase transition of CoCrNi HEAs is discussed. The theoretical values of lattice parameter a (x) increase with increasing Al concentration, which is consistent with the earlier experimental findings. The crystal structure transitions from the FCC to BCC crystal structure as the Al content increases. At x &amp;lt; 11.8 at. %, Al alloying lowers the elastic stability of the BCC and FCC phases, whereas excessive Al doping causes the FCC phase to BCC phase transition (x &amp;gt; 21.4 at. %). The crystal structure has an ideal mix phase of BCC and FCC at x = 18.8 at. %, which results in excellent strength-ductility synergy of HEAs. There is a phase transition point at x = 11.8 at. %, where there may be a competition between phase transition and dislocation nucleation, which improves strength. The work in this paper provides new ideas for the design of future high-performance duplex phase HEAs.

Microstructure, Mechanical Properties, and Lead–Bismuth Eutectic Corrosion Behaviors of FeCrAlY-Al2O3 Nanoceramic Composite Coatings

Seven FeCrAlY-Al2O3 nanoceramic composite coatings are deposited on F/M steel via plasma spraying and laser remelting. A systematic investigation is conducted to examine the dependence of microstructure, mechanical properties, and lead–bismuth eutectic (LBE) corrosion resistance on the nano-Al2O3 addition and different Cr and Al contents. With the increase in Al content in FeCrAlY, gradual refinement of the coating grains occurs. The addition of nano-Al2O3 promotes the elemental segregation and precipitation of the second phase. The nano-Al2O3 notably enhances the mechanical properties of the coatings that are primarily attributed to second-phase and fine-grain strengthening. After LBE corrosion tests, intergranular corrosion morphology could be observed, where the contents of Cr and Al significantly influence the corrosion behavior of the coatings at varying temperatures.

High-temperature corrosion behavior of the FeCrAl laser cladding coatings in waste-to-energy superheaters: Influence of Al content

Enhancing the high-temperature corrosion resistance of superheaters in waste-to-energy plants (WTE) is key to improving the efficiency of WTE power generation. The present study employed laser cladding technology to fabricate Fe-13Cr-xAl coatings, and characterized the microstructure, phase structure, and Vickers hardness of the coatings using OM, SEM, XRD, and a Vickers hardness tester. The study investigated the influence of high-temperature corrosion resistance of the coatings under simulated WTE flue gas conditions. This study found that: Al and Cr both exist in the form of solid solution atoms in the laser cladding coatings. The Vickers hardness of the coatings gradually increased with increasing Al content. When the Al content exceeds 10 %, cracks begin to appear in the coatings, and the number and size of cracks increase with increasing Al content. The Fe-13Cr-7Al coatings exhibit the best high-temperature corrosion resistance under simulated WTE flue gas conditions, and it can achieve ∼73 % of the high-temperature corrosion resistance of the Inconel 625 alloy laser cladding coatings. During high-temperature corrosion, phase separation occurs near the grain boundaries, resulting in chromium depletion zones, which promote intergranular corrosion of the coatings. During the process of high temperature corrosion, the reactions between Al, Cl, and S exhibit the lowest Gibbs free energy. The continuous consumption of Al effectively protects the Fe and Cr in the substrate. Additionally, the formation of aluminum oxide in the coating hinders the inward diffusion of Cl2, thereby beneficially impeding the progress of corrosion. Excessive Al contents in the coatings introduced cracks that served as channels for molten salt to penetrate the matrix, thereby reducing the high-temperature corrosion resistance of the coatings.

Effect of Al Content on Inclusions in Fe‐15Mn‐xAl‐C Low‐Density Steel

Three experiments of Fe‐15Mn‐xAl‐C (x = 1, 3, 5) low‐density steel with different Al contents are carried out, and the characteristics of inclusions are observed through field‐emission scanning electron microscopy. The results show that the types of inclusions in the three samples are almost the same, mainly Al2O3, AlN, MnS, TiN, Al2O3‐MnS, AlN‐MnS, TiN‐MnS, and Al2O3‐AlN‐MnS. The number percentage of Al2O3 decreases, while the number percentage of AlN increases with the increase of Al content in the three samples. As the Al content increases, the number of inclusions between 1 and 5 μm decreases, while the number between 5 and 10 μm increases. FactSage8.2 software calculation shows that an increase in Al content leads to an increase in the liquidus and a decrease in the solidus of the steel; at the same time, it causes the austenite region to narrow and expands the ferrite region. The change in the solidification route leads to a delay in the solidification fraction of AlN, MnS, and TiN inclusions precipitation. At last, the 2D mismatch theory shows that the mismatch degrees of Al2O3/MnS, AlN/MnS, TiN/MnS, and AlN/Al2O3 are 8.41%, 8.94%, 11.65%, and 11.66%, respectively.

Aluminum‐Based Chalcopyrite Thin Films and Solar Cells

AbstractAluminum‐based chalcopyrite materials have attracted attention because of the wide controllability range of their material properties and potential for use in energy‐conversion devices. Herein, CuAlSe2‐based thin‐film growth and solar cell device properties are discussed. Ternary CuAlSe2 thin films are relatively unstable and decompose weeks after film growth, even when preserved in a dry box. However, alloying with elemental In led to significant improvements in stability. Cu(In,Al)Se2 (CIAS) solar cells yield better photovoltaic performance than CuInSe2 cells, although the effective range of Al concentration that can improve device performance is narrower than that of elemental Ga in Cu(In,Ga)Se2 (CIGS). A decrease in the alkali metal concentration in CIAS films with increasing Al concentration is observed, indicating that the formation energy of alkali‐metal substitutional defects on the Cu site is high, and/or Al‐related complex defects formed are kinetically stable and difficult to replace with alkali metals once they form. Although the direct observation of alkali metals in the bulk (grain interior) of chalcopyrite CuInSe2 and CIGS films has been difficult to date, this result can serve as indirect evidence of the presence of alkali metals in the bulk of CuInSe2 films.

Slug-flow synthesis of NCMA: Effect of substitution of cobalt with aluminum on the electrochemical performance of Ni-rich cathode for lithium-ion battery

Nickle-rich Li[Ni1-x-yCoxMny]O2 (x, y ≤ 0.1) (NCM) layered materials are known as promising cathode materials for next-generation lithium-ion batteries and electric vehicles owing to their high-reversible capacity and operating voltage of up to 3.6 vs Li/Li+. However, issues, such as irreversible phase transition, cation mixing, microcrack formation, thermal and structural stability of the material prevent its widespread adoption. Although, cation doping is a well-known technique to enhance the electrochemical performance of the NCM-based cathode material, the performance of the material is very sensitive to the doping amount. In this study, three Al-doped quaternary Ni-rich cathode materials Li[Ni0.85Co(0.1-x)Mn0.05Alx]O2 (where, x = 0–0.04) (NCMA) are synthesized through three-phase slug-flow based continuous manufacturing process followed by high temperature calcination to study the effect of Al-doping on the performance of the cathode material while reducing Co. The slug flow-based production platform has several advantages, like particle size uniformity, high production rate, and homogeneity in elemental distribution. It is found that with an increase in Al content, the specific capacity decreases but the cyclic stability and rate capability increases. Optimum Al-doping not only compensates for the adverse effect of low Co by decreasing the extent of cation mixing, but it also minimizes the electrode polarization and cracking of the particles.

Unraveling the ecological mechanisms of Aluminum on microbial community succession in epiphytic biofilms on Vallisneria natans leaves: Novel insights from microbial interactions

The extensive use of aluminum (Al) poses an escalating ecological risk to aquatic ecosystems. The epiphytic biofilm on submerged plant leaves plays a crucial role in the regulation nutrient cycling and energy flow within aquatic environments. Here, we conducted a mesocosm experiment aimed at elucidating the impact of different Al concentrations (0, 0.6, 1.2, 2.0 mg/L) on microbial communities in epiphytic biofilms on Vallisneria natans. At 1.2 mg/L, the highest biofilms thickness (101.94 µm) was observed. Al treatment at 2.0 mg/L significantly reduced bacterial diversity, while micro-eukaryotic diversity increased. Pseudomonadota and Bacteroidota decreased, whereas Cyanobacteriota increased at 1.2 mg/L and 2.0 mg/L. At 1.2 and 2.0 mg/L. Furthermore, Al at concentrations of 1.2 and 2.0 mg/L enhanced the bacterial network complexity, while micro-eukaryotic networks showed reduced complexity. An increase in positive correlations among microbial co-occurrence patterns from 49.51% (CK) to 57.05% (2.0 mg/L) was indicative of augmented microbial cooperation under Al stress. The shift in keystone taxa with increasing Al concentration pointed to alterations in the functional dynamics of microbial communities. Additionally, Al treatments induced antioxidant responses in V. natans, elevating leaf reactive oxygen species (ROS) content. This study highlights the critical need to control appropriate concentration Al concentrations to preserve microbial diversity, sustain ecological functions, and enhance lake remediation in aquatic ecosystems.

Hot processing performance and fracture toughness control of AlxCrFeNiCu1.5 (x = 0, 0.2, 0.4, 0.6, 0.8) high entropy alloys

In order to develop high-entropy alloys with both good hot processing performance and fracture toughness, AlxCrFeNiCu1.5(x=0, 0.2, 0.4, 0.6, 0.8) alloys were designed and prepared. The alloy was firstly hot rolled by a twin-roll rolling device, and then the hot processing performance of the alloy under different Al contents was explored, whether the fracture toughness was at an ideal level, and if so, why it was at an ideal level. The results showed that the phase composition after hot rolling and annealing were two phases (face-centered cubic FCC and body-centered cubic BCC). With the increase of Al content, the FCC phase gradually transformed into BCC phase, and the increase of BCC phase led to the decrease of plasticity, which led to the decrease of hot processing performance. With the increase of Al content, the average fracture toughness value increased first and then decreased. Among them, the Al0.2CrFeNiCu1.5 and Al0.4CrFeNiCu1.5 alloys had the relatively better fracture toughness, which was because that the alloys had the appropriate proportion of FCC and BCC phases, and the strength and plasticity could achieve an ideal match. Among these alloys, the Al0.2CrFeNiCu1.5 alloy had the relatively better hot processing performance and ideal fracture toughness, and its average fracture toughness was 35.71 MPa·m1/2. And compared with Al0.2CrFeNiCu1.5 alloy, the Al0.4CrFeNiCu1.5 alloy had the worse hot processing performance, but it yielded the best fracture toughness, with an average value of 45.27 MPa·m1/2. In the crack propagation morphology, we found the main crack terminated at the notch upper part for the Al0.2CrFeNiCu1.5 alloy, suggesting that the material has good plasticity. And we also found crack multiple deflections and secondary cracking for the Al0.4CrFeNiCu1.5 alloy, which was helpful to improve the fracture toughness.

Effect of Al content on the microstructure, mechanical property and lead-bismuth eutectic corrosion resistance of refractory AlxTiNbZrMoV coatings produced by magnetron sputtering

In present study, refractory AlxTiNbZrMoV (x=0.2, 0.5, 0.9 and 1.2 in molar ratio) high-entropy alloy coatings were prepared by magnetron sputtering technology. The microstructure, mechanical property and lead-bismuth eutectic corrosion resistance of the AlxRHEA coatings were investigated. With the increase of Al content, the coatings maintained the amorphous structure, and no intermediate phase was generated. The hardness and elastic modulus of the AlxRHEA coatings were higher than that of Al-free coating. After the LBE corrosion, formation of surface Fe-oxide layer occurred in the four AlxRHEA coatings. The Al0.5RHEA and Al0.9RHEA coatings exhibited improved corrosion resistance. The results indicate that for HEA, the formation of protective alumina layer can be on the basis of Al enrichment on the coating surface to continue to improve the oxidation resistance.

Toward deeper ultraviolet detection: Atomic layer deposited amorphous AlGaOx thin film detector with its tunable optical properties and opto-electronic responses

Employing atomic layer deposition, AlGaOx films with varying Al concentrations (highest to 44% at.) were meticulously synthesized. Comprehensive characterization encompassing chemical composition, elemental depth distribution, structural clarity, and interface delineation unequivocally attested to the superior quality of the films. Optical properties were rigorously assessed using transmittance spectra and spectroscopic ellipsometry (SE), and optical constants across a broad spectral range (200–1000 nm) were determined through SE fitting. A consistent blue-shift in the absorption edge, observed in both the transmittance spectra and extinction coefficient, is attributed to the incorporation of aluminum. Detailed exploration via X-ray photoelectron spectroscopy fine scans of O 1s energy loss spectra and valence band analysis revealed that the evolution of the conduction band is instrumental in modulating the bandgap. To ascertain the viability for deep ultraviolet light detection, photodetectors based on AlGaOx were fabricated. Blue shifts in both photocurrent and response peak wavelength correlated with increasing Al content. In specific occasions, the AlGaOx-based detector has a responsibility of 0.05 A/W and 7×1013 detectivity of Jones. Remarkably, the detector demonstrates commendable on/off capability, characterized by fast rise and decay times of 0.26 s and 0.17 s, respectively. This study extensively examined the chemical, structural, and optical properties of amorphous AlGaOx films, alongside the optoelectronic capabilities of AlGaOx-based devices. Our research presented a viable strategy for enhanced deep ultraviolet detection, showcasing a successful implementation of amorphous bandgap engineering. This endeavor holds promise for future advancements in UV-detector development.

Dual wire arc additive manufacturing of compositionally graded Alx-Co-Cr-Fe-Ni high-entropy alloy

Graded materials are promising alloys due to their improved strength and ductility. In this study, a functionally graded Alx-Co-Cr-Fe-Ni high entropy alloy with a variation of Al concentration along the building direction was produced in-situ by dual wire arc additive manufacturing for the first time, and the microstructure and mechanical properties of the deposited alloy were investigated. The results showed that the FCC + BCC dual-phase gradually transformed to a single BCC phase with increasing Al content, the precipitation temperature of the ordered B2 phase became high, and the precipitation temperature range of the disordered BCC phase became wider, which promoted the formation of the disordered BCC phase. With the change in phase ratio, the hardness gradually increased from 342 HV to 397 HV, and the bottom deposited alloy had an optimal combination with a compressive strength of 827.4 MPa and elongation of 42.3%. Compared to the bottom region, the top region shows much higher sliding wear resistance. The high-density dislocations and grain refinement result in better toughness and strength in the bottom region, while the segregation of Cr elements at the grain boundaries changes the properties of the grain boundaries and makes them more brittle in the top region. This investigation realizes a novel method to fabricate GHEAs, which can produce a more convenient and cost-effective gradient material with a complex composition.

Reaction molecular dynamics study of calcium alumino-silicate hydrate gel in the hydration deposition process at the calcium silicate hydrate interface: The influence of Al/Si

Supplementary cementitious materials (SCMs) can partially replace cement in concrete production, forming calcium alumino-silicate hydrate (C-A-S-H). This enhances concrete durability while recycling waste. However, the early hydration reaction process of C-A-S-H and its deposition and aggregation behavior at the interface with the primary hydration product of cement, calcium silicate hydrate (C–S–H), remain unknown. Therefore, this study utilizes reactive molecular dynamics to model the deposition and growth behaviors of C-A-S-H precursors with different Al/Si ratios on C–S–H, and discusses the effects of the Al/Si ratio on C-A-S-H gel aggregation behavior and structural evolution at the C–S–H interface. The results show that increasing Al content significantly promotes the early hydration reaction rate of C-A-S-H gel, the degree of polymerization of silicate chains, and the amount of Qn(n ≥ 2) species. Moreover, higher Al content leads to the precursors aggregating among themselves rather than depositing on the C–S–H substrate surface. The incorporation of Al–O polyhedra can effectively bridge silicate chains on the C–S–H surface and alter the growth patterns of hydration products from linear chains to three-dimensional networks. This work provides molecular-level insights into the influences of the Al/Si ratio on the early hydration reaction process and interfacial deposition behaviors of C-A-S-H gel.

Effects of C and Al Alloying on Constitutive Model Parameters and Hot Deformation Behavior of Medium-Mn Steels.

Single-pass isothermal hot compression tests on four medium-Mn steels with different C and Al contents were conducted using a Gleeble-3500 thermal simulation machine at varying deformation temperatures (900-1150 °C) and strain rates (0.01-5 s-1). Based on friction correction theory, the friction of the test stress-strain data was corrected. On this basis, the Arrhenius constitutive model of experimental steels considering Al content and strain compensation and hot processing maps of different experimental steels at a strain of 0.9 were established. Moreover, the effects of C and Al contents on constitutive model parameters and hot processing performance were analyzed. The results revealed that the increase in C content changed the trend of the thermal deformation activation energy Q with the true strain. The Q value of 2C7Mn3Al increased by about 50 KJ/mol compared with 7Mn3Al at a true strain greater than 0.4. In contrast, increasing the Al content from 0 to 1.14 wt.% decreased the activation energy of thermal deformation in the true strain range of 0.4-0.9. Continuing to increase to 3.30 wt.% increased the Q of 7Mn3Al over 7Mn by about 65 KJ/mol over the full strain range. In comparison, 7Mn1Al exhibited the best hot processing performance under the deformation temperature of 975-1125 °C and strain rate of 0.2-5 s-1. This is due to the addition of C element reduces the δ-ferrite volume fraction, which leads to the precipitation of κ-carbides and causes the formation of microcracks; an increase in Al content from 0 to 1.14 wt.% reduces the austenite stability and improves the hot workability, but a continued increase in the content up to 3.30 wt.% results in the emergence of δ-ferrite in the microstructure, which slows down the austenite DRX and not conducive to the hot processing performance.

Investigation of the influence of Al layer and total film thicknesses on structural and related magnetic properties in sputtered Ni/Al multilayer thin films

The effects of parameters of Al layer thickness and total film thickness on the structural and related magnetic properties of Ni/Al multilayer films were investigated. The films were deposited by a dual sputtering. The Ni content decreased gradually while the Al content increased as the Al layer thickness increased. It was also observed that the total film thickness had little effect on the film content. All films have a face-centred cubic structure. And, the surface morphology of Ni/Al films is more uniform and homogeneous than the surface of Ni film. For magnetic analysis, the properties were strongly changed with the parameters. The saturation magnetisation, Ms of Ni film was obtained as 572 emu/cm3 while the Ms of the Ni/Al films decreased from 441 to 298 emu/cm3 with increasing Al content in the films caused by the Al layer thickness. And, the increase of total film thickness resulted in a decrease of Ms value. While the coercivity, Hc value of the Ni film was 90 Oe, Hc of Ni/Al films was decreased to ~ 39 Oe with the formation of multilayer structure. Ni/Al multilayers were obtained magnetically softer than the Ni film. The Ms and Hc values were significantly affected by the variation of the film content and crystal structure caused by the changes in deposition parameters. Therefore, this is a fundamental step for Ni/Al multilayers to improve the properties of these films for their potential applications in microelectronic devices.

Tetrahedral Amorphous Carbon Coatings with Al Incorporation Deposited by a Hybrid Technique of Sputtering and Arc Evaporation

In this paper, tetrahedral amorphous carbon (ta-C) coatings containing Al were deposited by a hybrid technique of sputtering and arc evaporation. The influence of Al incorporation in the structure and properties of the ta-C coatings were studied as a function of the Al concentration. It is found that Al tends to form a Al-O-C bond when the Al concentration is small. An Al-C bond was detected when the Al concentration is high. Al can facilitate the graphitization of the ta-C coatings and the graphite cluster size as well as the sp2/sp3 ratio of the coatings increase as the Al concentration increases. The decline of the sp3 fraction causes the drop in the hardness of the coatings. The incorporation of Al can effectively decrease the residual stress of the ta-C coatings. During friction tests, Al can facilitate the formation of the sp2-rich graphitic tribo-layer and decrease the friction coefficient. Nevertheless, the decline of the hardness due to the Al incorporation will result in the increase in the wear rate of the coating. It is believed that the ta-C coating with a proper concentration of Al appears to achieve a good comprehensive performance with high hardness, low residual stress, and a low friction coefficient and wear rate.

The Effect of Nb Doping on the Properties of Ti-Al Intermetallic Compounds Using First-Principles Calculations.

The crystal structures, stability, mechanical properties and electronic structures of Nb-free and Nb-doped Ti-Al intermetallic compounds were investigated via first-principles calculations. Seven components and eleven crystal configurations were considered based on the phase diagram. The calculated results demonstrate that hP8-Ti3Al, tP4-TiAl, tP32-Ti3Al5, tI24-TiAl2, tI16-Ti5Al11, tI24-Ti2Al5, and tI32-TiAl3 are the most stable phases. Mechanical properties were estimated with the calculated elastic constants, as well as the bulk modulus, shear modulus, Young's modulus, Poisson's ratio and Pugh's ratio following the Voigt-Reuss-Hill scheme. As the Al content increases, the mechanical strength increases but the ductility decreases in the Ti-Al compounds. This results from the enhanced covalent bond formed by the continuously enhanced Al-sp hybrid orbitals and Ti-3d orbitals. Nb doping (~5 at.% in this study) keeps the thermodynamical and mechanical stability for the Ti-Al compounds, which exhibit slightly higher bulk modulus and better ductility. This is attributed to the fact that the Nb 4d orbitals locate near the Fermi level and interact with the Ti-3d and Al-3p orbitals, improving the metallic bonds based on the electronic structures.

First-principles study of the mechanical and thermodynamic properties of aluminium-doped magnesium alloys.

Magnesium-aluminum (Mg-Al) alloys are widely used in aerospace, automobile and medical equipment owing to their advantages of easy casting, high strength-to-mass ratio and good biocompatibility. The structural, mechanical, electronic and thermodynamic properties of MgxAly alloys (x + y = 16, x = 1, 2,…, 15) with varying Al-doping contents were studied using the first-principles method. In this work, the structures of MgxAly alloys were constructed by replacing Mg atoms in a supercell with Al atoms. The lattice parameters of the Al-doped MgxAly alloys decrease with an increasing Al content because of the smaller atomic size of Al than that of Mg. The calculated formation energies show that Mg11Al5, Mg5Al3 and Mg9Al7 have prominent structural stability. The analyses of the mechanical properties reveal that the doping of Al improves the ductility of MgxAly alloys. The elastic moduli increase with an increasing Al content, and Mg9Al7 has a notable ability to resist deformation, while Mg11Al5 and Mg5Al3 have better plasticity. The calculated results of their electronic properties reveal that Mg11Al5, Mg5Al3 and Mg9Al7 are good conductors without magnetism. Furthermore, CDD analyses show that the inner layer charges of Al atoms migrated to the outer layer, and the charges of Mg atoms accumulated significantly in the outer region of Al atoms. The Debye temperature of Mg9Al7 is higher than that of Mg11Al5 and Mg5Al3, indicating that it has better thermodynamic stability. Our findings would be helpful for the design of Mg-Al alloys with excellent mechanical and thermodynamic performances.

Simulation of displacement damage induced by protons incident on Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ga&lt;sub&gt;1&lt;i&gt;–x&lt;/i&gt;&lt;/sub&gt;N materials

Gallium nitride materials, due to their excellent electrical properties and irradiation resistance, are expected to be used in future space electronics systems where electronic devices are composed of different amounts of Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ga&lt;sub&gt;1&lt;i&gt;–x&lt;/i&gt;&lt;/sub&gt;N materials. However, most of their displacement damage studies currently focus on GaN materials, and less on Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ga&lt;sub&gt;1&lt;i&gt;–x&lt;/i&gt;&lt;/sub&gt;N materials themselves. The mechanism of displacement damage induced by 10- keV- to-300- MeV protons incident on Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ga&lt;sub&gt;1&lt;i&gt;–x&lt;/i&gt;&lt;/sub&gt;N materials with different Al content is investigated by binary collision approximation method. The results show that the non-ionization energy loss of Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ga&lt;sub&gt;1&lt;i&gt;–x&lt;/i&gt;&lt;/sub&gt;N material decreases with proton energy increasing. When the proton energy is lower than 40 MeV, the non-ionization energy loss becomes larger with the increase of Al content, while the trend is reversed when the proton energy increases. Analyzing the primary knock-on atoms and non-ionizing energy deposition caused by protons, it is found that the primary knock-on atoms’ spectra of different Al&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Ga&lt;sub&gt;1&lt;i&gt;–x&lt;/i&gt;&lt;/sub&gt;N materials are similar, but the higher the content of Al, the higher the proportion of the self primary knock-on atoms generated by elastic collisions is. For the non-ionizing energy deposition produced by protons at different depths, the energy deposition due to elastic collisions is largest at the end of the trajectory, while the energy deposition due to inelastic collisions is uniformly distributed in the front of the trajectory but decreases at the end of the trajectory. This study provides a good insight into the applications of GaN materials and devices in space radiation environment.