Search Results (124)

This study proposes a novel synergistic design strategy to enhance the oxidation resistance of FeNiCuAl-based high-entropy alloys by integrating multi-element alloying (Cr-Co-Mn), trace Y modification, and laser-cladding-induced nanocrystallization. While the Base Alloy exhibited a mass gain of approximately 15 mg/cm² after oxidation at 900 °C for 120 h, the addition of Cr_2.5Co_2.5Mn_2.5 promoted the formation of a multilayered oxide scale (outer MnCr₂O₄/inner Al₂O₃), reducing the parabolic oxidation rate constant to 1.7 × 10⁻⁵ mg²·cm⁻⁴·s⁻¹. The originality of this work lies in the coupling of compositional and microstructural engineering; further addition of 0.5 at.% Y decreased this constant to 1.7 × 10⁻⁶ mg²·cm⁻⁴·s⁻¹—a three-order-of-magnitude reduction relative to the Base Alloy, while increasing the apparent oxidation activation energy to ~350 kJ/mol. After 100 thermal cycles at 1000 °C, the designed alloy showed a mass change of only 0.05 ± 0.02 mg/cm², with its critical load and interfacial fracture energy reaching 78 N and 14.8 J/m², respectively. Furthermore, the alloy retained a hardness of 310 HV, an elastic modulus of 135 GPa, and a tensile strength of 240 MPa at elevated temperature. These results demonstrate that the synergistic integration of chemical and structural optimization provides a new paradigm for designing low-cost, high-performance FeNiCuAl-based protective coatings. Full article

Machine learning interatomic potentials (MLIPs) are typically developed for globally ordered homogeneous systems (GOHomS), which exhibit only minor local deviations from equilibrium configurations. Consequently, most existing MLIPs trained on GOHomS often perform inadequately when applied to locally ordered heterogeneous systems (LOHetS), e.g., substitutional alloying elements in multicomponent alloys. To describe doping alloy systems, we develop a fine-tuned MLIP based on the MACE foundation model, specifically tailored for Mo-based dilute alloys containing one or two out of 20 substitutional elements: Cr, Fe, Mn, Nb, Re, Ta, Ti, V, W, Y, Zr, Al, Zn, Cu, Ag, Au, Hg, Co, Ni, and Hf. The model is built on more than 7000 equilibrium and non-equilibrium structures derived from first-principles density functional theory (DFT) calculations. The optimized large-scale fine-tuned model attains state-of-the-art accuracy, with a mean absolute error (MAE) and root-mean-square error (RMSE) of 2.27 meV/atom and 3.79 meV/atom for energy predictions, and 13.83 meV/Å and 24.26 meV/Å for force predictions, respectively. Systematic evaluation under different data-splitting protocols shows that unknown element extrapolation remains challenging under strict dopant hold-out, whereas substantially improved accuracy can be achieved in partial-exposure transfer settings. The fine-tuned models reduce the MAE by approximately 7–10 times compared to models trained from scratch, and by 10–20 times relative to zero-shot foundation models. This performance gain remains consistent across varying dataset sizes (equilibrium vs. non-equilibrium structures) and model scales. Our work illustrates the efficacy of transfer learning from globally ordered homogeneous systems to locally ordered heterogeneous multicomponent alloy environments. However, direct transfer to entirely unknown elements remains challenging, especially when proxy embeddings are employed without fine-tuning. Thus, to achieve high accuracy without incurring additional cost, it is essential to include unknown elements in the training dataset while minimizing the number of configurations containing known elements. Moreover, the current findings are primarily validated for dilute Mo-based alloy systems. Extending this approach to more compositionally complex alloy spaces may necessitate additional data and further fine-tuning. Full article

Two types of coatings, NiCrAlY and NiCrAlY/YSZ, were fabricated on the surface of M247 alloy by the atmospheric plasma spraying (APS) technique. Under pure Na₂SO₄ and 25 wt.% NaCl-containing mixed salt deposits at 900 °C in air, the M247 alloy underwent rapid catastrophic corrosion. The non-protective corrosion products formed on the surface included NiO and (Ni,Co)Cr₂O₄ spinel. The hot corrosion of M247 under the pure Na₂SO₄ salt deposit followed a basic fluxing mechanism, whereas under the NaCl-containing mixed salt deposit, it was dominated by an active oxidation mechanism. During hot corrosion, the NiCrAlY coating developed a continuous, dense, and highly protective α-Al₂O₃ oxide scale on its surface, endowing it with superior hot corrosion resistance. The thermal barrier coating of NiCrAlY/YSZ exhibited the best hot corrosion resistance, attributed to the physical barrier and thermal barrier effects of the outer YSZ ceramic layer. Full article

The trade-off between strength and ductility remains a pivotal challenge in the development of multi-principal element alloys (MPEAs) for structural applications. Here, we report a dual-scale ordering strategy to achieve triple strengthening in a Ni-26.6Co-18.4Cr-5.4Nb-4.1Mo-2.3Al-0.3Ti-0.05Y (wt.%) MPEA through the synergistic interplay of L1₂ nanoprecipitates and local chemical order (LCO). The alloy was processed via cold rolling followed by aging at 750 °C for 8 h, resulting in a high density of coherent L1₂ precipitates (average size 47 ± 1 nm, volume fraction ~27%) with an ultra-low lattice misfit of 0.5%. Additionally, sub-nanoscale LCO domains with an average diameter of 0.62 nm were identified within the face-centered cubic matrix. This hierarchical microstructure yields an exceptional combination of mechanical properties at room temperature: yield strength of 1480 ± 6 MPa, ultimate tensile strength of 1678 ± 10 MPa, and a total elongation of 13.9 ± 0.2%. Quantitative strengthening analysis reveals that precipitation strengthening (697 MPa) is the dominant contributor, followed by dislocation strengthening (397 MPa). Transmission electron microscopy characterization of deformed samples reveals that the low stacking fault energy, promoted by LCO, facilitates the dissociation of perfect dislocations and the formation of extensive stacking faults. The intersection of stacking faults on different {111} planes generates a large number of Lomer–Cottrell locks, which significantly enhance work hardening and delay plastic instability. The findings demonstrate that engineering dual-scale ordered structures offers a promising pathway for developing MPEAs with a superior strength-ductility combination. Full article

The horst and graben system in Western Anatolia lies on the eastern boundary of the Aegean extensional system, one of the most active extensional zones in the world. The Şahinali coal basin is located south of the Büyük Menderes Graben, which is part of this system. This study examines the rare earth elements and yttrium (REY) geochemistry, accumulation conditions, and economic potential of the Şahinali coals. Compared to world coals, the REE concentration in Şahinali coals (208.3 ppm) is quite high, and all REY groups are slightly enriched. Light REY (LREY) is dominant compared to medium REY (MREY) and heavy REY (HREY). The most abundant element in this group is Ce, reaching a concentration of 123.3 ppm. REY distribution patterns indicate H-type enrichment in most samples and, to a lesser extent, M-H-type enrichment. Element ratios (Al₂O₃/TiO₂, TiO₂/Zr, La/Sc, Co/Th) and REY anomalies (Ce, Eu, Gd) indicate that the sedimentary input is predominantly derived from felsic rocks, with limited intermediate to mafic contributions. SEM-EDS findings and correlation analyses indicate that REY are predominantly associated with aluminosilicate minerals. LREY-Th and MREY/HREY-Y relationships are supported by monazite and Y-rich illitic K-aluminosilicates. Paleoenvironmental indicators (V/Cr, Ni/Co, U/Th, Sr/Cu, Rb/Sr, Sr/Ba) indicate that the coal accumulated under oxic–suboxic, warm and humid conditions. The average REY oxide (REO) content slightly exceeds the commonly cited 1000 ppm screening threshold for coal ash. The majority of samples contain elevated proportions of critical REY (30.7%–54.3%) and show promising outlook coefficients (C_outl: 0.8–1.7). Together, these results indicate a favourable compositional signature for preliminary REY resource screening in the Şahinali coals, particularly with respect to elements relevant for high-technology applications. Full article

FeCoNiCrAl and FeCoNiCrAlScY high-entropy coatings were fabricated via electron beam physical vapor deposition. The microstructure and short-term isothermal oxidation behavior of the coatings were compared. Sc and Y inhibited coating element diffusion to the superalloy substrate and formed co-precipitated phases during coating manufacturing. The Sc/Y co-doped coating exhibited accelerated phase transformation from θ- to α-Al₂O₃ as compared to the undoped one. The effect mechanism associated with the nucleation of α-Al₂O₃ was discussed. The preferential formation of Sc/Y-rich oxides promoted the nucleation of α-Al₂O₃ beneath them, and the θ-α phase evolution process was directly skipped, which suppressed the rapid growth of θ-Al₂O₃ and the initial formation of cracks in the alumina film and provided the FeCoNiCrAl high-entropy coating with an improved oxidation property in the early oxidation stage. Full article

Thermal barrier coatings (TBCs) are critical for protecting hot-section components in gas turbines and aero-engines. Traditional yttria-stabilized zirconia (YSZ) coatings are prone to phase transformation and sintering-induced failure at elevated temperatures. This study fabricated CeScYSZ (4 mol% CeO₂ and 6 mol% Sc₂O₃ co-doped YSZ)/NiCrAlY TBCs using atmospheric plasma spraying (APS). A five-factor, four-level orthogonal experimental design was employed to optimize spraying parameters, investigating the influence of powder feed rate, spray distance, current, hydrogen flow rate and primary gas flow rate on the coating’s microstructure and mechanical properties. The resistance to calcium–magnesium–alumino–silicate (CMAS) corrosion was compared between CeScYSZ and YSZ coatings. The results indicate that the optimal parameters are a spray distance of 100 mm, current of 500 A, argon flow rate of 30 L/min, hydrogen flow rate of 6 L/min, and powder feed rate of 45 g/min. Coatings produced under these conditions exhibited moderate porosity and excellent bonding strength. After exposure to CMAS corrosion at 1300 °C for 2 h, the CeScYSZ coating demonstrated significantly superior corrosion resistance compared to YSZ. This enhancement is attributed to the formation of a CaZrO₃ physical barrier and the synergistic effect of Ce and Sc in suppressing deleterious phase transformations. This study provides an experimental basis for the preparation and application of high-performance TBCs. Full article

A Y-doped AlCoCrFeNi_2.1 eutectic high-entropy alloy was fabricated via powder bed fusion-laser melting/metal (PBF-LB/M), and the effects of the rare-earth element Y on its microstructure and mechanical properties were investigated. The results indicate that Y addition preserves the fine eutectic microstructure inherent to the PBF-LB/M process, while inducing lattice distortion within the face-centered cubic (FCC) matrix and promoting grain refinement. During solidification, Y facilitates heterogeneous nucleation and, due to its strong affinity with Al, increases both the volume fraction of the body-centered cubic (BCC) phase and the proportion of high-angle grain boundaries. X-ray diffraction (XRD) analysis further confirms that Y suppresses the formation of the ordered B2 phase. Tensile testing reveals that Y doping improves the tensile strength from 1383 MPa to 1475 MPa and enhances the elongation from 13.0% to 16.3%. Fractography shows a transition from quasi-cleavage to ductile fracture mode, indicating that Y significantly enhances the strength–ductility synergy of the alloy. Full article

Thermal barrier coatings (TBCs) extend gas-turbine blade lifetime by improving high-temperature oxidation resistance and mechanical performance. We investigated the microstructural evolution, TGO growth, and Al depletion in air-plasma-sprayed (APS) single-layer YSZ top coat over a NiCrCoAlY bond coat on Ni-based superalloy circular plates, heat treated isothermally at 850 °C and 1000 °C for 50–5000 h. Cross-sectional SEM/EDS analysis showed TGO quadratic thickening kinetics at both temperatures, reaching ~10 µm at 1000 °C/5000 h, the growth rate of which was ~5.8 times higher than at 850 °C. On top of the single-layer TGO of Al₂O₃ observed from the onset, a NiCrCo oxide layer appeared and grew from ≥500 h at 850 °C, with increasing growth rate and cracking. The layer configuration of the YSZ top coat, the TGO of Al₂O₃, and the bond coat (comprising β-NiAl and γ-NiCr) on top of GTD111, showed an Al concentration gradient in the bond coat starting at 850 °C for 250 h, which intensified with increased duration and temperature. The decrease in Al concentration in the bond coat and the growth of TGO are due to the dissolution of β-NiAl and subsequent Al diffusion to the Al₂O₃ TGO. Full article

The South Tianshan records the latest accretionary and collisional events in the southwestern Altaids, but the internal subduction-related processes are controversial. This study provides an integrative analysis of a newly identified Late Carboniferous adakitic granodiorite from the South Tianshan, incorporating geochronological, zircon U-Pb and Lu-Hf isotopic, whole-rock geochemical, and Sr-Nd isotopic data. Zircon U-Pb analysis indicates that the granite was emplaced at 310 ± 2.5 Ma. Based on major element compositions, the granodiorite belongs to medium-K calc-alkaline weakly peraluminous series (A/CNK = 0.95–1.09). The samples exhibit typical high-silica adakitic affinity, as evidenced by the elevated contents of SiO₂ (67.75–69.27 wt.%), Al₂O₃ (15.29–15.90 wt.%), Sr (479–530 ppm), and Ba (860–910 ppm); low concentrations of Yb (0.43–0.47 ppm) and Y (7.12–7.44 ppm); high Sr/Y ratios (67–72); and slight Eu anomalies (δEu = 0.89–1.03). The sodium-rich composition (K₂O/Na₂O = 0.48–0.71) is comparable to adakitic rocks from slab-derived melts. Elevated concentrations of Ni (22.12–24.25 ppm), Cr (33.20–37.86 ppm), Co (6.32–6.75 ppm), and V (30.33–32.48 ppm), along with high Mg# values (55–57), suggest melt–mantle interaction during magma ascent. The slightly enriched isotopic signatures, characterized by higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.706086–0.706205) and lower ε_Nd(t) (−3.09 to –2.47) and ε_Hf(t) (−3.11 to +7.66) values, point to notable sedimentary contributions, potentially through source contamination and/or shallow-level crustal contamination. By integrating the new results with previously published data, we consider that the adakitic granodiorite was generated by partial melting of the subducted oceanic crust, triggered by asthenospheric upwelling associated with the southward rollback of the north-dipping South Tianshan oceanic lithosphere. Our data provide new insights into Late Carboniferous retreating subduction along the southern active margin of the Yili-Central Tianshan and the accretionary architecture of the southern Altaids. Full article

The main purpose of this work is to suppress the rate of thermal and oxidative corrosion of copper substrates using double-ceramic-layer thermal barrier coatings (TBCs). Herein, the orthogonal spray experiment was employed to optimize the spraying parameters for TBCs consisting of Cu/NiCoCrAlY/8YSZ/(Y_0.5Gd_0.5)TaO₄. The thermal cycling and average mass loss rate of TBCs prepared by atmospheric plasma spraying (APS) with optimum spraying parameters correspond to 20 cycles and 0.56‰, respectively. The thermal conductivity (0.39 W·m⁻¹·K⁻¹ at 900 °C) of (Y_0.5Gd_0.5)TaO₄ is 71.68% and 52.7% lower than that of (Y_0.5Gd_0.5)TaO₄ bulk and 8YSZ, respectively. Meanwhile, the bond strength increased from 8.86 MPa to 14.03 MPa as the heat treatment time increased from 0 h to 24 h, benefiting from the heat treatment to release the residual stresses inside the coating. Additionally, the hardness increased from 5.88 ± 0.56 GPa to 7.9 ± 0.64 GPa as the heat treatment temperature increased from room temperature to 1000 °C, resulting from the healing of pores and increased densification. Lastly, crack growth driven by thermal stress mismatch accumulated during thermal cycling is the main cause of coating failure. The above results demonstrated that 8YSZ/(Y_0.5Gd_0.5)TaO₄ can increase the service span of copper substrate. Full article

Aircraft gas turbine blades operate in aggressive, generally oxidizing, atmospheres. A solution to mitigate the degradation and improve the performance of such components is the deposition of thermal barrier coatings systems (TBCs). High-velocity air fuel (HVAF) is a very efficient process for coating deposition in TBC systems, particularly for bond coats in aerospace applications. However, its low-temperature variant has received little attention in the literature and could be a promising alternative to limit oxidation during spraying when compared to conventional methods. This study has the main objective of analyzing how the geometry of the low-temperature HVAF gun influences the microstructure and the in-flight oxidation of MCrAlX coatings. To that end, a low-temperature HVAF torch is used to deposit MCrAlX coatings on a steel substrate with different nozzle lengths. In-flight particle diagnosis is used to measure the MCrAlX particle velocity, and to correlate to the nozzle geometry and to analyze its influence on the final coating. The microstructure of the coatings is assessed by scanning electron microscopy (SEM) and the material oxidation is analyzed and measured on a field emission scanning transmission electron microscope (FE-STEM) equipped with focused ion beam (FIB) and by Energy Dispersive Spectroscopy (EDS). Full article

Increasing demand to deposit dense and oxidation-resistant bond coats requires reliable and efficient deposition techniques. High-Velocity Air-Fuel (HVAF), among other thermal spray processes, is showcasing consistent potential to optimize spraying techniques and deposition strategies for depositing NiCoCrAlY coatings. NiCoCrAlY coatings are sensitive to high-temperature oxidation, and preserving the aluminum reservoir in the bond coats is of the highest priority to potentially resist oxidation during thermal cycling. Contrary to the existing literature on comparing carbide-based HVAF deposition with other processes, this work investigates the specific role of nozzle configurations. It primarily focuses on in-flight particle characteristics using diagnostic tools and the corresponding inflight particle oxidation of NiCoCrAlY feedstock. This work details individual splat and coating characteristics, revealing the significant influence of nozzle configurations. A comprehensive understanding of process–material–microstructure correlations was established using a commercially available NiCoCrAlY coating system. Comprehensive discussions on nozzle configurations over various feedstock powder characteristics were carried out in this work. Advanced characterization techniques were employed to assess the in-flight particle oxidation and coating microstructure using focused ion beam (FIB), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Full article

The Maramures region, located in North-Western Romania, was a renowned center of mining and smelting in the last century. Nowadays, all the mines have been decommissioned or are under conservation and greening works, but the acidic waters from some closed or abandoned mine galleries negatively affect the nearby streams and, in some cases, the entire river system. In this study, 46 elements and 6 anion concentrations were used to assess the pollution in 12 mine water discharge samples collected in two mining areas in Maramures. The results showed high concentrations of sulfate (average 1264 mg/L) and toxic elements, namely Mn (average 25.1 mg/L), Fe (average 23.0 mg/L), and Zn (average 12.5 mg/L). The sum of the REEs concentration ranged from 1.24 µg/L to 2917 µg/L, with an average of 363 µg/L, with La, Ce, and Nd being the most abundant. High correlations were found between REEs and Li, Be, Al, Sc, V, Mn, Fe, Co, Ni, Y, SO₄²⁻, and NO₂⁻. According to the pollution index, the discharge of mine water poses different degrees of ecological risk. The health hazard index calculated for 37 elements revealed an extremely high non-cancer risk and, in addition, an increased carcinogenic risk for Cd, As, and Cr. Full article