Al Content Research Articles

Pilot-Scale Aluminothermic Production of Silicon Alloy and Alumina-Rich Slag.

As global demand for silicon (Si) and alumina continues to surge, the significance of developing more sustainable production methods has intensified. The SisAl process represents a path-breaking approach to producing Si and alumina by utilizing side streams from the silicon and aluminum industries. In the present work, a comprehensive series of pilot-scale trials was conducted to assess the scalability and validity of the SisAl process. The influences of reductant raw materials, charging methods, input material ratios, and other processing parameters were also investigated. On coupling between thermodynamic calculations and experimental results, it was demonstrated that the SisAl process is stable and controllable at a pilot scale. The typical composition of the produced Si alloy ranges from 70 to 75 wt % Si, 15-18 wt % Ca, and 8-10 wt % Al. The produced CaO-Al2O3-based slag has a composition of 48-57 wt % Al2O3, 40-45 wt % CaO, and 3-13 wt % SiO2. Furthermore, various reductants, including Al blocks, dross, and scraps, were evaluated in the pilot trials, yielding comparable outcomes, with alloy composition differences only within approximately 3 wt % under the same parameter conditions, demonstrating the versatility of raw materials selection in the SisAl process. Moreover, it was found that acidic slag exhibited better features for future upscaling than the neutral slags, with a 5 wt % higher Si content in the alloy and a 4 wt % increase in Al2O3 content in the slag phase. Additionally, the chemical composition of the products was shown to be controllable by adjusting the stoichiometry of the input materials (Al/SiO2 ratio). As the charged stoichiometry increases from 1 to 1.2, the Si content in the alloy significantly decreases from 73 to 63 wt %, while the Al content correspondingly increases from 9 to 18 wt %. Further investigation into processing parameters, such as charging method, slag prefusion, and stirring methods, has also revealed valuable insights toward the continued upscaling of the SisAl process to a potentially innovative, sustainable, low-carbon industrial process.

Phase evolution at interface between magnesia refractories and low-density steel/slag by Mg/Ca mass transfer

This study investigated the interfacial phase evolution between magnesia refractory and low-density molten steel with different Al contents (0.5 % and 10 %) during the steel-slag reaction. Simulated experiments involving a refractory-steel-slag coupling reaction were conducted under laboratory conditions. The thickness and compositional distribution of the interface layers formed after the refractories were exposed to molten steel and slag were analyzed. The results indicate that, in the absence of slag, a MgAl2O4 layer is formed at the interface between the refractory and molten steel due to the reaction between [Al] and Al2O3 inclusions in the molten steel with the refractory. Upon the addition of slag, CaO in the slag is reduced to Ca and transferred into the molten steel, modifying the solid MgAl2O4 layer at the interface into a primarily liquid CaO·MgO·Al2O3 layer. The liquid interface intensified the erosion of the refractory by the molten steel, resulting in a thickened interface layer. The higher the Al content in the steel, the greater the degree of modification of the CaO·MgO·Al2O3 layer by Ca. The Mg/Ca mass transfer process during the steel-slag reaction was simulated using the FactSage Macros calculation, and the differences in mass transfer between low and high Al contents were compared. The results indicate that under high Al conditions, the supply of Mg/Ca increases significantly. The simulation results were compared with numerous findings in the literature, confirming the accuracy of the simulation.

Volcanism and turbidity current events as drivers of the evolution of benthic redox conditions: Organic matter enrichment in the Chang 7 member, Upper Triassic Yanchang formation, Ordos Basin, North China

Depositional events have a significant impact on the terrestrial redox conditions and provide evidence for studying the organic matter enrichment. The objective of this study was to evaluate the influence of volcanic and turbidity current events on benthic redox conditions during the Upper Triassic Chang 7 member (Ch7) of the Ordos Basin. To address these issues, the varying sedimentological settings, paleoredox conditions, and relationships between the redox environment and depositional events were investigated via sedimentary analysis of the profiles, microscopic analysis, organic geochemical analysis, and elemental geochemical data. The fine-grained sediments in the Chang 73 submember (Ch73) consist of abundant organic matter, collophanite, and framboidal pyrite. However, in the upper part of the Ch7 member, there was a decrease in organic matter, a decrease in the number of microorganisms, and an increase in pyrite size, indicating that the oxic environment is not favorable for organic matter enrichment. The element and geochemical proxies show similar vertical variations and redox changes. Volcanic activity can bring substantial amounts of material or elements to the basin. The enrichment of Hg and S exhibited considerable variation, ranging from 8.7 to 274.4 ppb and from 0.16 to 4.53 wt%, respectively, which influenced the organic matter accumulation through the flourishing and death of microorganisms and redox changes in the benthic environment of the terrestrial basin. As the lake basin shrinks, the Ti and Al contents increase with increasing frequency of turbidity current events, and the terrestrial debris transported to the lake basin gradually increases while carrying large amounts of oxygen and affecting sedimentation rates, contributing to the destruction of the reducing conditions of the benthic environment, subsequently, influencing organic matter accumulation. These results will be helpful in understanding the effect of multiple depositional events on organic matter enrichment in lacustrine basins.

Facile Determination of Aluminum Content in Industrial Brine by Investigating the Effects of Buffer Systems.

The aluminum content of concentrated (27 wt%) sodium chloride solutions could be crucial for large-scale chlor-alkali-based industries applying membrane cell electrolysis. Thus, a facile method which enables a fast and reliable protocol to determine the Al content of these solutions on ppb scale in industrial environments is fundamentally important. It was demonstrated that the increased sensitivity of colorful Al-ECR (eriochrome cyanine R) complex by the use of a cationic surfactant and specific biological buffers could effectively indicate the Al content in an extended pH interval of a concentrated saline medium under industrial conditions. The dependence of the analytical protocol on pH, temperature, time, wavelength, and the salinity of the medium was investigated. It was shown that the absorbance-based measurements of the solution should be performed at least 2-4 h after its preparation. By applying the selected two Good's buffers (HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, MOPS: 3-(N-morpholino)-propanesulfonic acid) and Tris (tris(hydroxymethyl)aminomethane), 32.8-38.1 % increase in the sensitivity was achieved for saturated NaCl solutions. Moreover, the limits of detection and quantification (LOD, LOQ) were also lowered by 19.0-29.8 %, and the salinity dependence of the calibration was also reduced.

Refining Alnico 8 magnets with composition optimization of matrix phase, directional solidification and magnetic field annealing

Optimized shape anisotropy of the Fe-Co rich ferromagnetic (α1) phase and the effective separation of the α1 and α2 phases with maximum magnetization difference—where α2 represents a paramagnetic magnetic phase—are the key parameters for maximizing the magnetic properties of Alnico magnets. In this manuscript, efforts have been undertaken to optimize the shape anisotropy of the α1 phase and increase the difference in magnetization and separation between α1 and α2 phases by fine tuning Al and Ni contents, directional solidification and magnetic field annealing methods. At first, Alnico magnets were fabricated by adjusting the content of α2 phase followed by homogenization, magnetic field annealing at high temperature, and low-temperature tempering. Intrinsic coercivity (Hcj) of ⁓146.0 kA/m, remanence (Br) of ⁓0.90 T and maximum energy density ((BH)max) of 46.02 kJ/m3 are achieved in the magnet with 8.2 wt% Al and 12.8 wt% Ni treated in field of 1.5 T for 10 minutes. At the second stage, the magnet with optimal magnetic properties is directionally solidified to develop columnar grains, and then the α1 phase is grown in the direction of the columnar grains by magnetic field annealing to enhance the (BH)max to 79.8 kJ/m3. The axial ratio of the α1 phase increased significantly with the increase of the grain size, particularly in the directionally solidified magnets. The Curie temperature of the α1 phase is noted near 1150 K, while the Curie temperature of the α2 phase is below 400 K. The magnets demonstrated excellent temperature stability, with magnetic properties decreasing by only 10–12 % at 800 K. These results may pave the way for further development of Alnico magnets specifically for high temperature applications.

Thermodynamic approach for designing processing routes of 4Mn quenching and partitioning steel

AbstractThe study addresses the design and optimization of chemical composition and processing routes of new quenching and partitioning medium-Mn alloy using theoretical and experimental approaches. The thermodynamic calculations using Thermo-Calc and JMatPro software were carried out to characterize the influence of Mn, Si and Al contents on cementite formation and precipitation processes. The evolution of individual phases as a function of temperature under thermodynamic equilibrium conditions was estimated. The investigations included the determination of continuous cooling transformation (CCT) and the time–temperature transformation (TTT) diagrams of a model 4Mn alloy. The calculated equilibrium diagrams were compared with the experimental diagrams determined using dilatometric tests. Microstructural observations were carried out to verify the results of dilatometric measurements. The results of thermodynamic calculations and experimental tests showed the moderate agreement. It is related to the inaccuracy of currently available models in the used software and/or non-equilibrium conditions of experimental tests.

Near-α titanium alloy dwell load-induced deformation twinning to coordinate the deformation mechanism associated with crack initiation

In this study, we identified a specific phenomenon of coordinated deformation of twins in near-α titanium alloys during dwell fatigue (DF). The main crack source regions and internal cracks in the micro-texture region (MTR) and no-MTR samples with inconsistent orientation characteristics were characterized. The results demonstrate that the main cracks in all specimens are aligned with the (0001) basal plane, which is associated with basal slip. Notably, twins are found and confirmed to be involved in the DF crack initiation process in high Al content near-α Ti60 alloys where deformation twins are rare, and tend to nucleate at the DF basal cracks. Further in-situ dwell investigation reveals and proposes that the dislocation pile-up and prismatic-basal (PB) interfacial features between soft/hard grains lead to deformation twin nucleation and growth from hard grain boundaries. Concurrently, the pyramidal 〈c+a〉 dislocation slip is observed to be in concurrent operation with the induced twins. These findings suggest that deformation twins not only coordinate basal grain deformation but also hinder the initiation and propagation of basal cracks caused by basal 〈a〉 slip. Moreover, a high density of pyramidal 〈c+a〉 dislocations within the twin and their dissociation to form basal stacking faults (SFTs) with a specific nanometric spacing make the twinning process accompanied by significant lattice distortions inside the twin. These newly formed nanotwin boundaries and SFTs act as barriers to dislocation motion, enhancing the strength and DF lifetime of near-α Ti60 alloys and effectively reducing the dwell sensitivity of no-MTR alloys. Our findings extend the understanding of the coordinated roles of dislocation slip, twin nucleation and formation of basal SFTs in near-α titanium alloys in dwell fatigue.

Optical absorption coefficient of a hydrogenic impurity in a surface quantum well

In this study, the first excited state binding energy and the linear, non-linear and total optical absorption coefficients (OAC) of a hydrogenic impurity in a surface quantum well (SQW) of the type vacuum/GaAs/AlxGa1-xAs are calculated as functions of the incident photon energy, the Al content and the well width using a variational method within the effective mass approximation. The results show that the first excited state energy and the linear, non-linear and total OAC are strongly influenced by variations in the well width, and only a slight, yet interesting, impact of the Al content is observed. A redshift in the extreme values of the linear, non-linear and total OAC is found for a SQW with fixed Al content and variable width, whereas no significant variation is observed in the reciprocal system of fixed width and variable Al content.

High Temperature Oxidation Behaviours of NiCoCrAlY alloys with High Al Content

Abstract MCrAlY coatings are of paramount importance in the protection of hot-end components from thermal oxidation and corrosion. The Al content is a crucial factor in enhancing the oxidation resistance properties of the coatings. This paper studies the oxidation behaviors of Ni-27.5Co-17Cr-xAl-0.5Y (x = 12 and 16 wt.%) alloys with high Al content. Following an oxidation process at 1100 °C over a period of 100 h, both alloys exhibit the oxide scales primarily consist of Al2O3 with minor amount of Co(Ni)Al2O4 spinels. The increased Al content results in a higher proportion of β phase, thereby promoting the development of an oxide scale in response to thermal exposure. This study provides insights into the fabrication of high Al content MCrAlY coatings with potential applications in next-generation thermal barrier coatings.

Preparation of porous (Mo2/3Y1/3)2AlC and its hydrogen evolution reaction performance

Porous (Mo2/3Y1/3)2AlC MAX phase ceramic was prepared by reaction sintering method using Mo, Y, Al, and graphite powder as raw materials. The influence of changes in Al content on the purity of the obtained samples was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Archimedes method, and bubble point method. The conditions for obtaining a pure phase were identified, and the transformation path of the phase during sintering and the mechanism of pore formation were provided. The linear sweep voltammetry (LSV) cure and cyclic voltammetry (CV) cure of MAX were tested using an electrochemical workstation. It can be calculated that MAX exhibits good hydrogen evolution reaction (HER) performance under alkaline conditions due to its high electrochemical active surface area (ECSA) of 373.2 and small Tafel slope of 41.7 ​mV·dec−1.

Construction of Mesoporous Aluminosilicate Thin Films on ITO Electrodes for Immobilizing a Cationic Ru(II) Water Oxidation Catalyst

Aluminosilicate (Al‐SiO2) thin films with vertically aligned mesochannels were successfully synthesized on ITO electrodes and employed for the immobilization of a cationic Ru(II) water oxidation catalyst without requiring linker groups. Optimal synthesis conditions yielded uniform mesoporous Al‐SiO2 films with tunable Al content, high surface area (568 m2/g), 3.94 nm pore size, and 155 nm thickness. Electrochemical studies confirmed the presence of the immobilized Ru complex undergoing diffusion‐controlled Ru(III/II) and Ru(IV/III) electron transfer. The Ru loading reached 4.71 nmol/cm2 at Si/Al = 9.6, with higher Al content enhancing loading amounts via cation exchange. The Ru‐modified electrode exhibited high electrocatalytic water oxidation activity, achieving 75.3% Faradaic efficiency and a turnover number of 298.6 for O2 evolution for 1 hour. This work provides a new approach to construct porous environments on an electrode surface to immobilize positively charged transition‐metal complexes as catalysts, offering potential applications in the development of electrocatalytic systems for energy conversion.

Influence of anionic silica forms in clear sodium silicate precursors on metakaolin geopolymerisation via 29Si and 27Al MAS-NMR and microstructural studies

A number of synthesis parameters directly influence the degree of reticulation/geopolymerisation of metakaolin exposed to alkaline solutions of sodium hydroxide and/or sodium silicate. In the latter case, a sodium silicate solution can be depolymerised by the introduction of an appropriate amount of NaOH. The effects of the ageing of the activator solution on the reticulation of metakaolin-based geopolymers are quantified for the first time in this work. We studied the anionic species of the sodium silicate solution with the addition of NaOH made just before the preparation of the paste, 24 h or 7 days before. These three ageing periods cause a significant difference in the Si-bearing species in solution, as demonstrated by nuclear magnetic resonance on 29Si. The effect of these anionic species on the reticulation/polymerisation of metakaolin at room temperature was demonstrated by solid-state 27Al and 29Si MAS-NMR, the chemical stability in various solutions (deionised water, HCl, HNO3, H2SO4), and X-ray diffraction on geopolymer powders before and after immersion in acids. Compressive strength before and after the immersion in acidic media was an additional measurement to assess the overall structural stability of the 3D polymerised network of the final dense ceramic-like product. Ageing of the activator solution affected the chemical stability of the hardened geopolymers accompanied by a slight to severe reduction in strength after leaching in HNO3 or HCl and in H2SO4, respectively. The quantitative MAS-NMR description of the Si and Al coordination in the geopolymers was correlated with the chemical stability where the formulations with the higher number of Q4(0Al) and Q4(1Al) for the silicon species were more resistant (lower number of Na+ compensating for Al+3 to be exchanged with H+). The formulations with higher Al content in the structure, i.e. higher number of Q4(3Al) silicon species showed higher mechanical stability. These results show that the timing of the preparation of the alkaline activator is essential for a correct mix design.

INAA of bone remains of Bohemian Duke John of Görlitz: an attempt to explain his sudden death at the age of twenty-five years

AbstractInstrumental neutron activation analysis (INAA) was employed to assay 32 minor and trace elements in bone of Bohemian Duke John of Görlitz (1370–1396) who suddenly died at the age 25 years for unknown reasons. Recently, histological examination of his illium bone was carried out, accompanied by histochemical staining reactions to learn about his health status. The INAA results disproved an elevated Al content indicated by the staining reaction with aluminon, but revealed elevated levels of Mn, As, Sb, and especially of Ag compared with literature values. The results are discussed in terms of toxicity of the above elements, especially whether their elevated levels could be the reason for Duke´s sudden death.

Regulations of Thermal Expansion Coefficients of Yb1−xAlxTaO4 for Environmental Barrier Coatings Applications

Environmental barrier coatings (EBCs) are widely used to protect ceramic matrix composites (CMCs, SiCf/SiC, and Al2O3f/Al2O3), and they should have low thermal expansion coefficients (TECs) matching the CMCs and excellent mechanical properties to prolong their lifetime. Current EBC materials have disadvantages of phase transitions and insufficient mechanical properties, which affect their working temperatures and lifetime. It is necessary to develop new oxide EBCs. Ytterbium tantalate (YbTaO4) is a stable and novel EBC material, and we have improved the mechanical properties and TECs of Yb1−xAlxTaO4 (x = 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) ceramics by replacing Yb with Al. XRD, SEM, and EDS are used to verify the crystal and microstructures, and nano-indentation is used to measure the modulus and hardness when changes in TECs are measured within a thermal expansion device. The results show that the phase structure of Yb1−xAlxTaO4 (x = 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) is stable at 25–1400 °C within air atmosphere, and their high-temperature TECs (6.4–8.9 × 10−6 K−1, 1400 °C) are effectively regulated by introductions of different contents of Al, which enlarge their engineering applications for SiCf/SiC and Al2O3f/Al2O3 CMCs. The evolutions of TECs are analyzed from structural characteristics and phase compositions, and the increased TECs make Yb1−xAlxTaO4 potential EBCs for Al2O3 matrixes. Due to the high bonding strength of Al–O bonds, hardness, as well as Young’s modulus, are enhanced with the increasing Al content, with Yb1−xAlxTaO4 (x = 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) having a nano-hardness of 3.7–12.8 GPa and a Young’s modulus of 100.9–236.6 GPa. The TECs of YbTaO4 are successfully regulated to expand their applications, and they match those of Al2O3 and SiC matrixes, as well as displaying improved mechanical properties. This work promotes applications of YbTaO4 as potential EBCs and provides a new way to regulate the TECs of tantalates.

Effect of chemical inhomogeneity on the structure and properties of the two-layer TiAl-based coating obtained by non-vacuum electron beam cladding: Experimental investigations and density functional theory simulations

Non-vacuum electron beam cladding is a highly effective technology for producing protective coatings on metal workpieces. In this study, the 3.8 mm thick TiAl-based coating with Cr and Nb additions was obtained on the Ti alloy substrate in two passes of the electron beam. To evaluate inhomogeneity of the two-layer coating, energy-dispersive synchrotron X-ray diffraction (EDSXRD) in combination with energy-dispersive X-ray spectroscopy (EDX) was applied. It was found that in the direction from the top of the coating to the substrate, the dilution of the cladding layers with Ti increased. It influenced the phase constitution of the coating and led to a variation in the chemical composition of different phases (α2-Ti3Al, β-phase, and TiN). The properties of the first (lower) and the second (upper) cladding layers were evaluated separately. The upper layer exhibited greater oxidation resistance than the lower one due to the presence of the γ-phase, which has superior high-temperature stability compared to the α2-Ti3Al phase, predominant in the coating. The influence of varying chemical composition on the oxidation resistance was also estimated using density functional theory (DFT) simulations. It was found that decrease in Al content in the α2 phase leads to an increase in oxygen absorption energy. This could potentially result in a decrease in oxidation resistance. Wear resistance of the first and the second cladding layers was at the same level mainly due to the low contribution of minor phases. Additionally, DFT simulations show that the variations in chemical composition of the major phase (Ti3Al) are not likely to impact the coating wear resistance.

EFFECT OF APPLICATION METHODS AND RATES OF CALCIUM SOURCES ON SOIL ALUMINUM FORMS

Effect of application methods and rates of calcium sources on soil aluminum forms. The presence of aluminum (Al) in available forms in the soil can harm cultivated plants. Aluminum forms were evaluated in a Humic Cambisol soil grown with eucalyptus and treated with dolomitic limestone (DL), gypsum (GYP), and lime mud (LM), using surface applications over the total area (TA), to the planting strip (STRIP), and to the planting furrow with incorporation (FRW). The treatments were: Control; DL 3.5 Mg ha-1 TA; DL 1.75 Mg ha-1 STRIP; DL 3.5 Mg ha-1 STRIP; LM 3.5 Mg ha-1 STRIP; DL 3.5 Mg ha-1 + GYP 1.75 Mg ha-1 STRIP; DL 1.75 Mg ha-1 FRW; DL 1.75 Mg ha-1 + GYP 1.38 Mg ha-1 FRW; and GYP 1.38 Mg ha-1 FRW. After 31 and 56 months of applying the treatments, the levels of exchangeable Al (Al3+), Al bound to organic matter (Al - MO) and Al bound to low crystallinity and amorphous oxides (Al - OX) were determined in layers of up to 0.40 m. Al3+ contents decreased in the 0-0.05 m layer when DL and LM were applied in TA and STRIP and, in the lower layers when the first was incorporated in the FRW. Al-OM and Al-OX contents were 2.6 to 5.8-fold higher than Al3+. DL on TA decreases Al3+, Al-OM, and Al-OX contents in the 0-0.05 m layer. GYP application did not affect soil Al contents.

Optimization of high-temperature thermal pretreatment conditions for maximum enrichment of lithium and cobalt from spent lithium-ion polymer batteries

Due to their increasingly high demand, lithium-ion batteries (LIBs) will encounter a scarcity of essential resources if recycling is not prioritized. The current pretreatment methods for spent LIBs used in industrial production are inefficient, costly, and hazardous. The study aimed to maximize the yield of lithium and cobalt from the black mass of spent Lithium-ion batteries through an optimized high-temperature thermal pretreatment process, which combined mechanical (direct crushing) and thermal treatments to facilitate the subsequent recovery of these valuable metals. Sieve analysis showed that direct crushing for 2 min resulted in 40.81 % of the anode material in the 4750 + 2500 μm size range, while 5 min of crushing led to a more even distribution, with 28.57 % in the smallest size range (−75 μm). Heat treatment followed by 2 min of crushing concentrated 52.38 % of the anode material in the 4750 + 2500 μm range. For the cathode material, 2 min of direct crushing distributed 24.49 % in the −2500 + 1250 μm range, while 5 min of crushing accumulated 38.80 % in the −75 μm range. Heat treatment and 2 min of crushing resulted in 56.05 % of the cathode material in the −75 μm range, indicating improved liberation. The combination of heat treatment and mechanical treatment effectively liberates and reduces the size of the active materials, resulting in a higher cumulative mass fraction of finer particles (≤630 μm). Heat treatment at 600 °C for 15 min, followed by 2 min of crushing, dissociated current collectors (Al) from the cathode material, minimized the harmful gas emissions and produced fine particles (630 μm) with minimal Al content (0.8 wt%). The optimal heat treatment condition of 600 °C for 35 min achieved complete decomposition of PVDF and enriched 73.49 wt% cobalt and 5.41 wt% lithium in the black mass, superior to previous studies.

Solidification precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys

AlN inclusions are the major inclusions in FeCrAl alloys and precipitate during solidification. The precipitation behaviour and growth kinetics of AlN inclusions in FeCrAl alloys were theoretically calculated based on the Clyne–Kurz model and a diffusion-controlled growth model. The results indicated that AlN inclusions precipitated at a solid fraction of 0.45. Following precipitation, the Al concentration exhibited a slight decrease compared to scenarios where AlN inclusion precipitation was not considered, although it still showed an increasing trend. Conversely, the N concentration exhibited a significant turnaround, gradually dropping below its initial value. In addition, varying the cooling rate to 0.17, 0.83, 1.67, and 16.67 K/s, the final sizes of AlN inclusions were 46.5, 21.1, 14.8, and 4.7 μm, respectively. Fixing other factors, the solid fractions for AlN precipitation at initial Al concentrations of 4.19, 4.69, and 5.19 wt% were 0.535, 0.45, and 0.365, respectively, and the final sizes of AlN inclusions were 16.2, 14.8, and 13.6 μm, respectively. Similarly fixing the other factors and varying the initial N concentrations to 0.0045, 0.0053, and 0.0060 wt%, the solid fractions of AlN were 0.515, 0.45, and 0.40, respectively, and the final sizes of AlN inclusions were 14.6, 14.8, and 15.0 μm, respectively. This indicates that increasing the cooling rate, increasing the initial Al concentration, and decreasing the initial N concentration could effectively reduce the precipitation size of AlN inclusions. This work provides guidance for the investigation of the precipitation and growth kinetics of AlN inclusions in FeCrAl alloys.

Improving the oxidation resistance by forming continuous Al2O3 protective layer in alumina-forming austenitic stainless steel

The effect of varying aluminum (Al) levels on the high-temperature oxidation resistance of Alumina-Forming Austenitic stainless steels (AFA) has been investigated under dry air conditions at 800 °C and 900 °C. Mass gain assessments indicate that AFA stainless steel containing a higher concentration of Al, with a composition of Fe-20Ni-15Cr-2.4Al-1.6Mn, demonstrates enhanced resistance to oxidation when contrasted with steel of lower Al content, characterized as Fe-23Ni-15Cr-1.9Al. This phenomenon is attributed to the development of a compact CrMn1.5O4 layer on the exterior and an Al2O3 layer on the interior. The dense oxide layers that form on the high-Al steel impede the permeation of oxygen and deter the peeling of the oxide layer, thus preserving structural stability of the material upon exposure to high temperatures. Conversely, the steel with a lower Al content undergoes considerable chipping of its oxide layer. The morphology and distribution of Al2O3 are determined by the relative rates of oxygen inward movement and aluminum outward movement. In the case of the Fe-20Ni-15Cr-2.4Al-1.6Mn steel, the tight oxide film significantly reduces the inward movement of oxygen and increases the outward movement of Al, leading to a denser Al2O3 layer underneath the Cr2O3.

High-throughput preparation and quick characterization of oxidation behaviors of complex Al–Cr compositional gradient coatings on a novel Co–Al–W–based superalloy prepared using multi-arc ion plating technology

The early oxidation behaviors of complex Al–Cr compositional gradient coatings on a novel Co–Al–W substrate prepared by multi-arc ion plating technology (MIPT) at 1000 °C for 20–60 min were rapidly characterized. The as-deposited coatings with compositions ranging from (55%–90%Al, 45%–10%Cr) exhibited the laminated structure α-Al + Al80Cr20+Al8Cr5+α-Cr. After annealing at 640 °C for 40 h, a two-layered coating composed of (Co(Al, Cr) + Al8Co18Cr4) and IRL formed, and the thickness of the coating increased from the 14–18 μm of the as-deposited state to 25–35 μm. During oxidation at 1000 °C for 20–60 min, a three-layer structure consisting of an outer α-Al2O3+α-Cr2O3+CoCr2O4 layer, a central unoxidized Al–Cr layer, and an inner μ-Co7(W0.55Cr0.45) 6+B2–CoAl layer formed on the substrate. The Al–Cr coatings with higher Cr content had a looser oxide layer due to the CoCr2O4 phase, which might degrade the intended protective effect of the Al–Cr coatings. Thus, the Al–Cr coatings with higher Al content were suitable for preventing oxidation behavior. This work proposes a high-throughput screening method for rapid characterization of the early oxidation mechanism of the complex Al–Cr compositional gradient coatings.