Search Results (683)

Critical metals associated with aluminum-bearing strata have garnered increasing attention due to their considerable economic potential. Recent investigations have identified notable enrichment of Li, Ga, Zr, Nb, REEs (rare earth elements), etc., within the Upper Carboniferous Benxi Formation in the Yangquan mining area, the Northeastern Qinshui Basin, Northern China. However, their mineralogical characteristics and micro-scale modes of occurrence remain insufficiently constrained. In this study, we employed the TESCAN Integrated Mineral Analyzer (TIMA) in combination with X-ray diffraction (XRD) and clay-separation experiments to provide direct mineralogical evidence for the occurrence of Ti, Li, Ga, Zr, and REEs in claystone and aluminous claystone from the Benxi Formation, Yangquan mining area, Northeastern Qinshui Basin. Our results indicate that both lithologies are primarily composed of kaolinite and diaspore, with minor amounts of anatase and cookeite; illite is additionally present in the claystone. Titanium predominantly occurs as anatase in both lithologies, though a portion in aluminous claystone may be incorporated into kaolinite and other Ti-bearing minerals such as rutile and leucoxene. Lithium is primarily hosted by cookeite in both rock types. Mineral assemblage variations further suggest that kaolinite may have partially transformed into Li-rich chlorite (i.e., cookeite) during the transformation from aluminous claystone to claystone. Gallium is chiefly associated with diaspore and kaolinite, with a stronger correlation with diaspore in the aluminous claystone. Zircon is the sole carrier of Zr in both lithologies. Importantly, La and Ce show a consistent spatial association with O–Al–Si–Ti–P mixed aggregates in TIMA maps, particularly in aluminous claystone. Based on these spatial patterns, textural relationships, and comparisons with previous studies, phosphate minerals are inferred to be the dominant REE hosts, although minor contributions from other phases cannot be completely excluded. These findings highlight a previously underexplored mode of critical-metal enrichment in Northern Chinese bauxite-bearing strata and provide a mineralogical basis for future extraction and utilization. Full article

B is considered a valuable additive for TiAl alloys, because it is believed to improve their properties by refining their microstructures. However, the effects of B on the practical properties of TiAl alloys for jet engine blades and the optimal addition amount for achieving balanced properties remain unclear. Specifically, there have been very few studies to date in which the practical properties of alloys have been evaluated across a wide range of B addition levels. Therefore, we evaluated various reliability, cost, and performance properties of jet engine blade materials using cast Ti-45,47Al-2Nb-2Mn (the same as XD alloys), with varying B addition levels. The results showed that, in some cases, low B addition levels (0.1–0.2 at.%) could enhance the impact resistance and high-cycle fatigue performance. However, even low B addition levels negatively impacted the machinability, castability, and creep strength. Further, adding 0.4 B or more significantly reduced most practical properties. Compared to XD alloys, TiAl4822 exhibited a superior balance, which is attributed to the higher B content (1 at.%) in XD alloys and the greater effectiveness of Cr relative to Mn in improving the alloy’s high-temperature impact resistance. Full article

Multi-principal element nitrides have great application potential in protective coatings. However, the investigation of the oxidation and corrosion resistance of multi-principal element nitride coatings is still insufficient. The synthesis and high-temperature performance of AlCrNbSiTiN multi-principal element nitride coatings fabricated through optimized arc ion plating (AIP) were explored. Leveraging the high ionization efficiency and ion kinetic energy characteristic of AIP, coatings with significantly fewer internal defects were obtained. These coatings demonstrate superior mechanical properties, including a maximum hardness of 36.5 GPa and critical crack propagation resistance (CPR) values approaching 2000 N². Optimal coatings exhibited exceptional water vapor corrosion resistance (5.15 at% O after 200 h). The coatings prepared at −150 V had the optimal corrosion resistance, with the coating resistance and corrosion current density being 1.68 × 10⁴ Ω·cm² and 0.79 μA·cm⁻², respectively. AlCrNbSiTiN coatings produced under these optimized AIP conditions exhibit remarkably high-temperature oxidation, highlighting their potential for use in demanding engineering applications. Full article

TiAl alloys are ideal candidates to replace nickel-based superalloys in aero-engines due to their low density and high specific strength, yet their industrial application is hindered by narrow heat treatment windows and unbalanced mechanical performance. To address this, this study investigates the microstructure and mechanical properties of Ti-44.9Al-4.1Nb-1.0Mo-0.1B-0.05Y-0.05Si (TNM-derived) alloys hot-rolled in the (α₂ + γ) two-phase region. The research employs varying heat treatment temperatures (1150–1280 °C) and cooling rates (0.1–2.5 °C/s), combined with XRD, SEM, EBSD characterization, and 800 °C high-temperature tensile tests. Key findings: Discontinuous dynamic recrystallization (DDRX) of γ grains is the primary mechanism refining lamellar colonies during deformation. Higher heat treatment temperatures reduce γ/β phases (which constrain colony growth), increasing the volume fraction of lamellar colonies but exerting minimal impact on interlamellar spacing. Faster cooling shifts γ lamella nucleation from confined to grain boundaries to multi-sites (grain boundaries, γ lamella peripheries, α grains) and changes grain boundaries from jagged and interlocking to smooth and straight, which boosts nucleation sites and refines interlamellar spacing. Fine lamellar colonies and narrow interlamellar spacing enhance tensile strength, while eliminating brittle βo phases and promoting interlocking boundaries with uniform equiaxed γ grains improve plasticity. Full article

Skarn-type iron ore is economically significant, and numerous skarn ore deposits have been identified in the North China Craton. The newly discovered orbicular diorite in this region is distinguished from other analogous rocks due to the accumulation of large magnetite particles, which may shed new light on the genesis of this ore type. The magnetite in different parts of the orbicular structure exhibits distinct compositional differences. For example, magnetite at the edge has a small particle size (200 μm) and is associated with the minerals plagioclase and hornblende, indicating that it crystallized from normal diorite magma. By contrast, magnetite in the core has a relatively large particle size (>1000 μm), is associated with apatite and actinolite, and contains apatite inclusions as well as numerous pores. The size of magnetite in the mantle falls between that of the edge and the core. The syngenetic minerals of magnetite in the mantle include epidote and plagioclase. The magnetites in the cores of orbicules have a higher content of Ti, Al, Ni, Cr, Sc, Zn, Co, Ga, and Nb than those in the rim. The δ⁵⁶Fe value of the core magnetite (0.46‰–0.78‰) is much higher than that of the mantle and rim magnetite in orbicules. Moreover, the δ⁵⁶Fe value of magnetite increases as the V content of magnetite gradually decreases. This large iron isotope fractionation is likely driven by liquid immiscibility that forms iron-rich melts under high oxygen fugacity. The reaction between magma and carbonate xenoliths (Ca, Mg)CO₃ during magma migration generates abundant CO₂, which significantly increases the oxygen fugacity of the magmatic system. Under the action of CO₂ and other volatile components, liquid immiscibility occurs in the magma chamber, and Fe-rich oxide melts are formed by the melting of carbonate xenoliths. Iron oxides (Fe₃O₄/Fe₂O₃₎ will crystallize close to the liquidus due to high oxygen fugacity. These characteristics of magnetite in the Tanling orbicular diorite (Wuan, China) indicate that diorite magma reacts with carbonate xenoliths to form “Fe-rich melts”, and skarn iron deposits are probably formed by the reaction of intermediate-basic magma with carbonate rocks that generate such “Fe-rich melts”. A possible reaction is as follows: diorite magma + carbonate → (magnetite-actinolite-apatite) + garnet + epidote + feldspar + hornblende + CO₂↑. Full article

Ti₂AlNb-based alloys are potential structural materials for high-temperature applications due to their low density and superior specific strength. However, their widespread application is limited by relatively poor oxidation resistance above 700 °C. While Ti₂AlNb-based alloys exhibit promising mechanical properties, their oxidation behavior remains inadequately characterized, particularly concerning the role of Nb content. In this study, the high-temperature oxidation behavior of Ti₂AlNb-based alloys with different Nb contents was investigated at 800 °C in air. The results revealed a characteristic double-layered oxide structure consisting of an outer TiO₂ layer and inner alternating TiO₂-rich and AlNbO₄-rich sublayers. Thermodynamic calculations confirmed the favorable formation of TiO₂, Al₂O₃, Nb₂O₅, and AlNbO₄ at high temperatures. However, the reaction between Nb₂O₅ and Al₂O₃ hinders the formation of a protective Al₂O₃ layer. Increasing the Nb content was found to replace Ti atoms, reducing the diffusion rate of oxygen and simultaneously decreasing the thickness of porous TiO₂ regions. Nevertheless, the inadequate rate of aluminum diffusion inhibited adequate Al₂O₃ formation, leading to limited overall oxidation protection. These findings elucidate the composition–oxidation relationship in Ti₂AlNb-based alloys and provide valuable insights for tailoring Nb and Al contents to achieve a balanced combination of mechanical properties and high-temperature oxidation resistance. Full article

Particle accelerators are powerful tools in fundamental research, medicine, and industry that provide high-energy beams that can be used to study matter and to enable advanced applications. The state-of-the-art particle accelerators are fundamentally constructed from superconducting radio-frequency (SRF) cavities, which act as resonant structures for the acceleration of charged particles. The performance of such cavities is governed by inherent superconducting material properties such as the transition temperature, critical fields, penetration depth, and other related parameters and material quality. For the last few decades, bulk niobium has been the preferred material for SRF cavities, enabling accelerating gradients on the order of ~50 MV/m; however, its intrinsic limitations, high cost, and complicated manufacturing have motivated the search for alternative strategies. Among these, sputter-deposited superconducting thin films offer a promising route to address these challenges by reducing costs, improving thermal stability, and providing access to numerous high-T_c superconductors. This review focuses on progress in sputtered superconducting materials for SRF applications, in particular Nb, NbN, NbTiN, Nb₃Sn, Nb₃Al, V₃Si, Mo–Re, and MgB₂. We review how deposition process parameters such as deposition pressure, substrate temperature, substrate bias, duty cycle, and reactive gas flow influence film microstructure, stoichiometry, and superconducting properties, and link these to RF performance. High-energy deposition techniques, such as HiPIMS, have enabled the deposition of dense Nb and nitride films with high transition temperatures and low surface resistance. In contrast, sputtering of Nb₃Sn offers tunable stoichiometry when compared to vapour diffusion. Relatively new material systems, such as Nb₃Al, V₃Si, Mo-Re, and MgB₂, are just a few of the possibilities offered, but challenges with impurity control, interface engineering, and cavity-scale uniformity will remain. We believe that future progress will depend upon energetic sputtering, multilayer architectures, and systematic demonstrations at the cavity scale. Full article

The low-temperature impact properties of high-heat-input steels, particularly low-carbon Nb–Ti steel, are significantly influenced by the coarse-grained heat-affected zone (CGHAZ) in welded joints. The microstructure predominantly consists of granular bainitic ferrite (GBF), ferrite side plate (FSP), degenerate pearlite (DP), coarse plate-like ferrite (PF), and limited acicular ferrite (AF). This study investigates the effect of lanthanum (La) addition to Nb–Ti steel, leading to the formation of composite inclusions with a LaAlO₃·TiN core surrounded by MnS/MnC precipitates. Unlike conventional Al₂O₃·MnS inclusions in Nb–Ti steel, these La-modified inclusions promote enhanced AF nucleation. This not only refines prior austenite grains but also reduces detrimental microstructural constituents such as GBF and FSP. As a result, the impact energy at −40 °C significantly improves from 23 J (Nb–Ti steel) to 137 J (Nb–Ti–La steel). Moreover, the inclusions exhibit an increase in size but a decrease in number density. The Nb–Ti–La variant demonstrates a higher AF volume fraction and increased AF density within the CGHAZ. The refined grain structure, along with an increased proportion of high-angle grain boundaries, effectively impedes secondary crack propagation. These microstructural modifications contribute to a substantial improvement in the low-temperature impact toughness of welded joints. Full article

This study investigates TNM-type titanium aluminide alloys, representing the third generation of β-stabilized γ-TiAl heat-resistant materials. The aim of this work is to study the combustion characteristics and to produce compact materials via the free SHS compaction method from initial powder reagents taken in the following ratio (wt%): 51.85Ti–43Al–4Nb–1Mo–0.15B, as well as to determine the effect of high-temperature isothermal annealing at 1000 °C on the structure and properties of the obtained materials. Using free SHS compression (self-propagating high-temperature synthesis), we synthesized compact materials from a 51.85Ti–43Al–4Nb–1Mo–0.15B (wt%) powder blend. Key combustion parameters were optimized to maximize the synthesis temperature, employing a chemical ignition system. The as-fabricated materials exhibit a layered macrostructure with wavy interfaces, aligned parallel to material flow during compression. Post-synthesis isothermal annealing at 1000 °C for 3 h promoted further phase transformations, enhancing mechanical properties including microhardness (up to 7.4 GPa), Young’s modulus (up to 200 GPa) and elastic recovery (up to 31.8%). X-ray powder diffraction, SEM, and EDS analyses confirmed solid-state diffusion as the primary mechanism for element interaction during synthesis and annealing. The developed materials show promise as PVD targets for depositing heat-resistant coatings. Full article

Beta (β)-type Ti-29Nb-13Ta-4.6Zr (TNTZ) alloys combine low modulus with biocompatibility but require improved surface properties for long-term implantation. This study aimed to enhance the surface mechanical strength and antibacterial performance of TNTZ by applying TiN and TiAlN coatings via PVD. Notably, TiAlN was deposited on TNTZ for the first time, enabling a direct side-by-side comparison with TiN under identical deposition conditions. Dense TiN (~1.06 μm) and TiAlN (~1.73 μm) coatings were deposited onto solution-treated TNTZ and characterized by X-ray diffraction, scanning probe microscopy, Vickers microhardness, Rockwell indentation test (VDI 3198), static water contact angle measurements, and a Kirby–Bauer disk-diffusion antibacterial assay against Escherichia coli (E. coli). Both coatings formed face-centered cubic (FCC) structures with smooth interfaces (Ra ≤ 5.3 nm) while preserving the single-phase β matrix of the substrate. The hardness increased from 192 HV (uncoated) to 1059 HV (TiN) and 1468 HV (TiAlN), and the adhesion quality was rated as HF2 and HF1, respectively. The surface wettability changed from hydrophilic (48°) to moderately hydrophobic (82°) with TiN and highly hydrophobic (103°) with TiAlN. Similarly, the diameter of the no-growth zones increased to 18.02 mm (TiN) and 19.09 mm (TiAlN) compared to 17.65 mm for uncoated TNTZ. The findings indicate that TiAlN, in particular, provided improved hardness, adhesion, and hydrophobicity. Preliminary bacteriostatic screening under diffusion conditions suggested a modest relative antibacterial response, though the effect was not statistically significant between coated and uncoated TNTZ. Statistical analysis confirmed no significant difference between the groups (p > 0.05), indicating that only a preliminary bacteriostatic trend— rather than a definitive antibacterial effect—was observed. Both nitride coatings strengthened TNTZ without compromising its structural integrity, making TiAlN-coated TNTZ a promising candidate for next-generation orthopedic implants. Full article

In this study, various characterization techniques were utilized to investigate the effects of heat treatments on the microstructure and mechanical properties of Ti-48Al-3Nb-1.5Ta (at. %) alloy prepared by the supreme-speed plasma rotating electrode process and hot isostatic pressing. By comparing the microstructures of the alloy under different heat treatments conditions, it was found that the nearly lamellar structure with a size of about 145 μm is formed by a simple heat treatment (1400 °C/10 min, FC to 1300 °C, AC, 850 °C/3 h/FC). Under this heat treatment condition, the alloy exhibited satisfied mechanical properties, with a tensile fracture strain of 1.2% at room temperature and a tensile fracture strain of 7.5% at 750 °C. No fracture occurred after 225 h when creeping at 750 °C/250 MPa. Ta inhibited the growth of lamellae and the expansion of pores, thereby improving creep performance. In summary, the TiAl alloy with satisfied performance was obtained through a simple heat treatment process, which provides a significant idea for engineering application. Full article

As the residual products of severe chemical weathering, bauxite deposits serve both as essential economic Al-Fe resources and geochemical archives that reveal information about the parent rocks’ composition, paleoenvironments and paleoclimates, and the tectonic settings responsible for their genesis. The well-developed Early Paleocene bauxite deposits of the Salt Range, Pakistan, provide an opportunity for deciphering their ore genesis and parental affinities. The deposits occur as lenticular bodies and are typically composed of three consecutive stratigraphic facies from base to top: (1) massive dark-red facies (L-1), (2) composite conglomeratic–pisolitic facies (L-2), and (3) Kaolinite-rich clayey facies (L-3). Results from optical microscopy, X-ray powder diffraction (XRPD), and scanning electron microscopy with Energy-Dispersive X-Ray Spectroscopy (SEM-EDS) reveal that facies L-1 contains kaolinite, hematite, and goethite as major minerals, with minor amounts of muscovite, quartz, anatase, and rutile. In contrast, facies L-2 primarily consists of kaolinite, boehmite, hematite, gibbsite, goethite, alunite/natroalunite, and zaherite, with anatase, rutile, and quartz as minor constituents. L-3 is dominated by kaolinite, quartz, and anatase, while hematite and goethite exist in minor concentrations. Geochemical analysis reveals elevated concentrations of ${\mathrm{Al}}_2$${\mathrm{O}}_3$, ${\mathrm{Fe}}_2$${\mathrm{O}}_3$, ${\mathrm{SiO}}_2$, and ${\mathrm{TiO}}_2$. Trace elements, including Th, U, Ga, Y, Zr, Nb, Hf, V, and Cr, exhibit a positive trend across all sections when normalized to Upper Continental Crust (UCC) values. Field observations and analytical data suggest a polygenetic origin of these deposits. L-1 suggests in situ lateritization of some sort of precursor materials, with enrichment in stable and ultra-stable heavy minerals such as zircon, tourmaline, rutile, and monazite. This facies is mineralogically mature with bauxitic components, but lacks the typical bauxitic textures. In contrast, L-2 is texturally and mineralogically mature, characterized by various-sized pisoids and ooids within a microgranular-to-microclastic matrix. The L-3 mineralogy and texture suggest that the conditions were still favorable for bauxite formation. However, the ongoing tectonic activities and wet–dry climate cycles post-depositionally disrupted the bauxitization process. The accumulation of highly stable detrital minerals, such as zircon, rutile, tourmaline, and monazite, indicates prolonged weathering and multiple cycles of sedimentary reworking. These deposits have parental affinity with acidic-to-intermediate/-argillaceous rocks, resulting from the weathering of sediments derived from UCC sources, including cratonic sandstone and shale. Full article

As emergent material candidates for extreme environments, refractory high-entropy alloys (HEAs) or refractory multi-principal-element alloys (RMPEAs) comprising refractory metals feature qualities such as high radiation tolerance, corrosion resistance, and mechanical strength. A set of MoNbTi-based RMPEA samples with Al, Cr, V, and Zr additions are prepared by spark plasma sintering and investigated for their response to irradiation using 10 MeV Si⁺ ions with a dose of $1.43\times {10}^{15}$ ions/cm². Positron annihilation spectroscopy and transmission electron microscopy are employed as atomic- and meso- scale techniques to reveal how chemical complexity, nanotwinning, and phase fractions play an important role in radiation-induced defect accumulation and damage tolerance. The study provides experimental evidence of nanotwinning acting as an effective sink for radiation-induced point defects. Full article

In this study, the electrochemical corrosion behavior of TiAlZrTaNb nitride thin films deposited on 304 stainless steel substrates was investigated. The thin films were synthesized using high-power impulse magnetron sputtering (HiPIMS) and are classified as high-entropy alloys (HEAs). The microstructure, morphology, and chemical composition of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), respectively. Corrosion resistance was evaluated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests, employing tap water, acetic acid, and citric acid solutions at room temperature as electrolytes. The results demonstrated that the TiAlZrTaNbN coating exhibits a dense and homogeneous structure with a uniform elemental distribution. XRD analysis revealed the presence of face-centered cubic (FCC) crystalline phases, which significantly contribute to the coating’s corrosion resistance. Furthermore, the coating displayed exceptional corrosion performance in both acetic acid and citric acid electrolytes—simulating food environments with a pH ≤ 4.5—as revealed by a substantial reduction in corrosion current density and a positive shift in corrosion potential. These findings provide valuable insights into the properties of TiAlZrTaNbN coatings and underscore their potential for enhancing the durability of mechanical components employed in the food industry. Full article

High-entropy alloys (HEAs) exhibit superior properties for extreme environments, yet the effects of laser scanning speed on the microstructure and performance of laser-clad NiAlNbTiV HEA coatings remain unclear. This study systematically investigates NiAlNbTiV coatings on 316 stainless steel fabricated at scanning speeds of 800–1100 mm/min via laser cladding. Characterizations via XRD, SEM/EDS, microhardness testing, high-temperature wear testing, and electrochemical measurements reveal that increasing scanning speed enhances the cooling rate, promoting γ-(Ni, Fe) solid solution formation, intensifying TiV peaks, and reducing Fe-Nb intermetallics. Higher speeds refine grains and needle-like crystal distributions but introduce point defects and cracks at 1100 mm/min. Microhardness decreases from 606.2 HV (800 mm/min) to 522.4 HV (1100 mm/min). The 800 mm/min coating shows optimal wear resistance (wear volume: 0.0117 mm³) due to dense eutectic hard phases, while higher speeds degrade wear performance via increased defects. Corrosion resistance follows a non-linear trend, with the 900 mm/min coating achieving the lowest corrosion current density (1.656 μA·cm⁻²) due to fine grains and minimal defects. This work provides parametric optimization guidance for laser-clad HEA coatings in extreme-condition engineering applications. Full article