Search Results (538)

Continuous alumina (Al₂O₃) fibers are critical reinforcement materials for ceramic matrix composites (CMCs) utilized in extreme high-temperature environments. While their baseline thermal and mechanical properties are well-documented, their long-term service reliability in complex, multi-field environments—specifically coupled thermal, hygral, and atmospheric conditions—remains insufficiently quantified. This study systematically investigates the degradation mechanisms of alumina ceramic fiber ropes subjected to simulated engine exhaust atmospheres and cyclic rain exposure. By integrating macroscopic tensile testing with rigorous multi-scale microstructural characterizations (SEM, XRD, TGA, and advanced surface chemical state analyses via EDS and XPS), a comprehensive degradation model is proposed. Our findings reveal a pronounced two-stage mechanical degradation behavior: an initial catastrophic strength collapse followed by a stabilization phase. We elucidate that the initial embrittlement is governed not merely by thermal damage, but fundamentally by the hydrothermal volatilization and depletion of the surface amorphous SiO₂ binder, which annihilates the inter-fiber cooperative load-sharing capability. Concurrently, quantitative XPS and XRD analyses strongly suggest that the internal amorphous grain-boundary films undergo rapid structural rearrangement and crystallization, effectively homogenizing the microstructure and shifting the fracture mechanics from energy-dissipative crack deflection to unhindered brittle cleavage. After the preferential depletion of the amorphous silicate phase, the exposed α-Al₂O₃ core dictates a stabilized mechanical response. This research provides critical theoretical frameworks and experimental evidence for the life-cycle assessment and microstructural optimization of advanced oxide ceramic fibers in next-generation aerospace applications. Full article

Al₂O₃:Cr³⁺ coatings were synthesized on tungsten substrates by plasma electrolytic oxidation in a phosphate-aluminate electrolyte containing dispersed Cr₂O₃ nanoparticles, and their structural, photoluminescent, and temperature-sensing properties were investigated. The coatings exhibited a typical porous PEO morphology with a uniform thickness of approximately 31 μm, and EDS analysis confirmed the incorporation of Cr species from the electrolyte, with Cr content increasing with the concentration of Cr₂O₃ particles. XRD analysis showed that the coatings were composed predominantly of α-Al₂O₃, with minor contributions from metastable γ-Al₂O₃, confirming that our previously established process for forming the thermodynamically stable α-Al₂O₃ phase directly on a non-aluminum substrate remains robust upon the introduction of dopant nanoparticles. The Al₂O₃:Cr³⁺ coatings displayed characteristic ruby-like photoluminescence, including broad excitation bands associated with the ⁴A₂⟶⁴T₁ and ⁴A₂⟶⁴T₂ transitions and sharp R-line emission arising from the spin-forbidden ²E⟶⁴A₂ transition. The strongest emission was obtained for coatings prepared with 0.05 g/L Cr₂O₃, while higher concentrations resulted in concentration quenching. Temperature-dependent photoluminescence revealed two complementary thermometric mechanisms: R-line spectral shifting and thermally induced redistribution between the ²E and ⁴T₂ emissions. The deconvolution-based intensity-ratio approach provided a stronger temperature response than simple spectral partitioning, demonstrating the potential of PEO-derived Al₂O₃:Cr³⁺ coatings on tungsten as robust luminescent temperature-sensing layers. Full article

Secondary aluminum dross (SAD) from the aluminum industry is a hazardous residue that restricts sustainable aluminum production. Residual aluminum nitride (AlN) and insoluble fluorides after conventional pretreatment are major barriers to the safe utilization of SAD. In this study, a low-temperature intensified roasting–alkaline leaching process was developed to remove harmful elements by using reaction heat and waste heat to expose enveloped AlN and fluoride phases, form soluble sodium-bearing compounds, and intensify AlN oxidation. Without additives, roasting at 750 °C for 3 h converted 91.65% of AlN, leaving 1.37% AlN in the roasted SAD. With Na₂O₂ as an oxygen donor in situ, NaF as a mineralizer to reduce roasting temperature, and sodium-bearing species as reactants for soluble NaAlO₂/Na₂SiO₃ formation, the AlN conversion increased up to 97.01% under 5% NaF and 2.5% Na₂O₂ at 750 °C for 3 h. Afterwards, higher temperature, longer duration, lower roasted SAD dosage, and higher caustic soda concentration all improved fluorine removal in the subsequent alkaline leaching. Under 100 g/L Na₂O, 20 g/L roasted SAD, and 100 °C, fluorine and chlorine removal efficiencies reached 92.52% and 99.47%, respectively. The final high-alumina residue contained 74% Al₂O₃, mainly in the forms of α-Al₂O₃, NaAl₁₁O₁₇, and MgAl₂O₄, with only 0.19% F and 0.03% Cl, making it suitable for the preparation of various alumina-bearing materials and alumina production. Full article

To improve the wear resistance of 45 steel, nano-agglomerated Al₂O₃-TiO₂-CeO₂/carbon nanotubes (CNT) composite powders were prepared by spray drying and ball milling, followed by plasma spraying to fabricate coatings. The effect of CNT content on microstructure and wear resistance was investigated. The powders showed uniform size and high sphericity. Coatings mainly consisted of α-Al₂O₃, γ-Al₂O₃, and TiO₂. CNT addition refined grain size to 18.3 ± 1.1 nm. The high thermal conductivity of CNT reduced unmelted particles, improving coating density and element uniformity. Average coating thickness was 200 μm. When the CNT content reached 3 wt.%, the coating porosity decreased to 5.01 ± 0.72%. TEM analysis indicated that CeO₂ was mainly located at the grain boundaries. Moreover, the interfaces between CNT (002) and CeO₂ (220) appeared clean and well-bonded. As CNT content increased, microhardness and wear resistance first increased then decreased. At 3 wt.% CNT, the volumetric wear rate was 0.87 ± 0.15 × 10⁻⁵ mm³·N⁻¹·m⁻¹, representing an 8.46-times improvement in wear resistance compared to the substrate. The presence of CeO₂ enhanced the surface activity of CNT, facilitating the formation of lubricating films during friction and contributing to the superior wear resistance of the composite coating. Full article

Additively manufactured definitive restorative materials have gained popularity recently. The current in vitro study evaluated the effects of surface treatment and thermocycling on the shear bond strength (SBS) between four 3D-printed definitive restorative materials and a self-adhesive resin cement (SARC). Disc-shaped specimens were fabricated from four printable materials: two composite materials, Crowntec (Crowntec) and CRS Composite (Custom Resin Solutions), and two ceramic-filled composites, Alias Dental Crown (Alias) and Permanent Crown (PC) (n = 12 per subgroup). Specimens were divided into four surface treatment subgroups: control, 9% hydrofluoric acid etching (HF), 50 µm aluminum oxide (Al₂O₃) airborne-particle abrasion (S50), and 110 µm Al₂O₃ airborne-particle abrasion (S110). SARC was applied using Teflon molds ($\varnothing 3 \times 3 \mathrm{m}\mathrm{m}$). After all specimens were stored in water at 37 °C for 24 h, half of the specimens were subjected to 10,000 thermocycles. Subsequently, SBS testing was performed for all specimens. Data were analyzed using Kruskal–Wallis and Mann–Whitney U tests (α = 0.05), and failure modes were classified microscopically. Before thermocycling, compared with control groups, HF significantly decreased SBS in Crowntec, whereas S110 significantly increased SBS in Alias (p < 0.05). After thermocycling, surface-treated CRS and Alias groups showed significantly higher SBS than controls (p < 0.05); Crowntec showed increased SBS after HF and S50, and Permanent Crown only after S50. No significant differences were found among control groups (p > 0.05). Surface-treated groups exhibited mainly mixed and cohesive failures. Surface treatments generally improved the SBS after thermocycling. Full article

Ti–6Al–4V is the primary titanium alloy for aerospace, biomedical, and additive manufacturing applications; however, the high cost of powders produced by atomization limits their widespread adoption. This study aims to develop a cost-effective method for producing chemically homogeneous pre-alloyed Ti–6Al–4V powders from titanium sponge. A combined process is proposed, involving the hydrogenation of titanium sponge, mechanical alloying of the hydride phase with Al and V powders, and subsequent vacuum dehydrogenation. The formation of the brittle δ-TiH₂ phase facilitated intensive material comminution and effective distribution of the alloying elements. According to laser diffraction data, the median particle size decreased from 450 to 30–35 µm. X-ray diffraction (XRD) analysis confirmed the sequential α-Ti → δ-TiH₂ transition and the formation of a stable α + β two-phase structure characteristic of Ti–6Al–4V following dehydrogenation. SEM observations demonstrated that the final powders predominantly consist of individual fractured particles with limited hard agglomeration, favorable for powder flowability and compaction behavior. EDS analysis indicated a relatively homogeneous microscale distribution of Al and V without observable large-scale segregation. The synthesized powders exhibited low impurity levels, with O < 0.07 wt.% and H < 0.02 wt.%. The developed approach represents a promising and economical alternative to expensive atomization techniques for powder metallurgy and additive manufacturing. Full article

This industrial-scale study investigates cerium’s effect on inclusions, microstructure, and mechanical properties in Ti-bearing high-strength steel BT700L through comparative trials of two production batches (with/without 0.0035% Ce). Characterization via SEM/EDS, automatic inclusion analysis, and Factsage thermodynamic simulations revealed that Ce addition reduced spherical Al-Mg-Ca-O-S inclusions (from 24 to 7 per 2 mm²; size decreased from 17 μm to 10 μm) while promoting composite inclusions with AlCeO₃-Ca(Mn)S cores and Ce-containing Ti(C)N shells. Although square Ti(C)N inclusion numbers remained stable, their average size increased from 8 μm to 11 μm. Ce addition eliminated banded microstructure and refined grains through heterogeneous nucleation (Ce₂O₃ exhibits low misfit of 4.00% with α-Fe). Mechanically, yield strength increased marginally (<5%) with unchanged tensile strength and reducing elongation. However, −20 °C impact toughness decreased by 22%. This duality—beneficial grain refinement versus detrimental coarsening of angular TiN inclusions acting as stress concentrators—provides critical insights for optimizing Ce addition in industrial Ti-bearing high-strength steel BT700L. Full article

Thermal shock resistance is a critical parameter for evaluating the long-term service reliability of protective coatings in high-temperature molten-salt environments. In this study, Al₂O₃–Y₂O₃ composite coatings containing 0, 2, 5, and 8 wt.% Y₂O₃ were fabricated on 316L stainless-steel substrates by atmospheric plasma spraying (APS). Their phase constitution, microstructure, mechanical properties, and thermal shock resistance were systematically investigated. The results showed that, with increasing Y₂O₃ content, the relative content of α-Al₂O₃ gradually increased, whereas the coating densification, microhardness, and fracture toughness first increased and then decreased. After 200 thermal shock cycles, the thermal shock resistance of the Al₂O₃–Y₂O₃ composite coatings followed the order of 5 wt.% Y₂O₃ > 2 wt.% Y₂O₃ > 8 wt.% Y₂O₃ > 0 wt.% Y₂O₃, indicating that the addition of an appropriate amount of Y₂O₃ significantly improves the thermal shock resistance of the coatings. Analysis of the failure mechanism further revealed that the addition of an appropriate amount of Y₂O₃ enhanced phase stability and optimized the coating microstructure, thereby improving the crack-propagation resistance and ultimately enhancing the thermal shock resistance. In contrast, excessive Y₂O₃ weakens this beneficial effect because of increased microstructural heterogeneity and a higher defect density. Full article

Understanding the atomic-scale formation of anodic oxide films is critical for Al electrolytic capacitors. The formation mechanism and dielectric properties of an ultra-high-voltage anodized Al foil were investigated by combining experiments, reactive molecular dynamics, and first-principles calculations. Results indicate that film growth is primarily governed by the (011) crystal plane, and the density of the oxide film increases with the applied electric field. The diffusion barrier of H atoms (0.54 eV) is significantly lower than that of O atoms (1.41 eV), suggesting the preferential formation of Al hydroxide oxide species on the surface. As the anodization voltage increases, the oxide undergoes phase evolution from AlOOH to γ-Al₂O₃ and finally to α-Al₂O₃. First-principles calculations reveal the dielectric constants of alumina, which are 7.96 for AlOOH, 21.80 for γ-Al₂O₃ (Paglia structure), and 10.24 for α-Al₂O₃. These findings provide a theoretical basis for optimizing the microstructure and dielectric performance of ultra-high-voltage anodized Al foils. Full article

Ti-6Al-4V thin-walled specimens were fabricated by gas tungsten arc welding-based wire arc additive manufacturing under controlled oxygen concentrations of 1, 500 and 1000 ppm, with ambient air used as a severe oxygen-exposure reference. The effects of oxygen concentration on oxygen uptake, microstructure, oxidation behavior and mechanical properties were investigated. Within the controlled range, the internal oxygen content increased from 0.07 to 0.15 wt.%, remaining below the ASTM B381-2013 limit. These specimens retained sound interlayer bonding and were mainly composed of α-Ti with a small amount of β-Ti, without detectable crystalline TiO₂ by X-ray diffraction. Controlled oxygen uptake refined the α lamellae and increased deformation resistance through interstitial solid-solution strengthening, increasing hardness from approximately 320 HV to 330–350 HV and tensile strength from 880 to 940 MPa, while reducing elongation from 11.5% to 9.5%. In contrast, the ambient-air specimen reached an oxygen content of 0.36 wt.%, developed an approximately 90 μm oxidation-affected layer and showed TiO₂-related oxides, α-colony aggregation and interface weakening. Its tensile strength and elongation decreased sharply to 295 MPa and 1.9%, respectively. These results indicate that atmosphere control in WAAM Ti-6Al-4V should prevent the transition from controlled oxygen strengthening to excessive oxygen-induced embrittlement. Full article

Nickel–aluminum bronze (NAB) propellers can be severely damaged by the synergistic action of chloride corrosion and solid–liquid erosion in marine environments. However, the direct application of micro-arc oxidation (MAO) to NAB is fundamentally hindered because NAB is a non-valve metal. Herein, this limitation is circumvented via a novel hybrid strategy integrating friction stir welding (FSW) and MAO. A defect-free aluminum transition layer is first fabricated onto NAB by FSW and thinned to ~30 μm for MAO. An Al₂O₃-based composite ceramic coating is synthesized, exhibiting a duplex structure with α/γ-Al₂O₃ and an amorphous Si-O network. The coating demonstrates a nano-hardness of 16.2 ± 2.0 GPa and an elastic modulus of 251.3 ± 31.1 GPa, underpinned by a robust interfacial tensile strength of 72.7 MPa. In 3.5 wt.% NaCl, the corrosion current density is suppressed to 1.335 ± 0.151 × 10⁻⁷ A/cm², while the charge transfer resistance reaches 3.072 × 10⁵ Ω·cm². Mass loss after 30-day immersion is reduced to ~1/11 of NAB, and erosion loss at 400 rpm is ~1/8 of that of the substrate. Electrochemical results indicate that the Al transition layer provides an initial beneficial contribution, while the MAO ceramic coating further delivers the dominant barrier protection, together leading to the best overall corrosion resistance of the hybrid-treated sample. Full article

The corrosion behavior and time-dependent mechanism of 22MnB5 steel featuring a thinned Al-Si coating (60 g/m²) were systematically investigated in a chloride ion wet–dry cyclic environment, motivated by the demand for thinning and toughening development of aluminum-silicon coatings. A periodic immersion accelerated corrosion test using 3.5% NaCl solution was conducted, together with macro/microscopic morphology observation (SEM/EDS), phase analysis (XRD, FTIR), and electrochemical measurements (polarization curves, EIS). The Al-Si coated steel was studied over corrosion periods of 1, 8, 10, and 20 days to elucidate its corrosion behavior, interfacial evolution, and failure mechanism. The results indicated that the corrosion process exhibited a three-stage evolution: stable protection, rapid failure, and dynamic equilibrium. At the initial stage (1 day), a dense Al₂O₃ passive film formed on the coating surface, providing excellent substrate protection, with a corrosion current density of only 1.77 µA/cm² and a maximum charge-transfer resistance (R₂) of 652 Ω·cm². In the middle stage (8 days), Cl⁻ permeated through the cracked film, triggering selective dissolution of Al, while Si was enriched in situ to form a porous residual layer; the corrosion current density (I_corr) sharply increased to 13.25 µA/cm², and R₂ dropped to its minimum of 156.6 Ω·cm². Corrosion products at this stage were mainly Al₂O₃ and SiO₂, accompanied by small amounts of iron oxyhydroxides and hydroxides, and local coating failure began to appear. During the later stage (10–20 days), the corrosion products evolved into γ-FeOOH, α-FeOOH, and Fe₂O₃, which, together with an amorphous SiO₂ gel network enriched at the interface, formed a dual-layer composite rust layer. R2 consequently recovered from 156.6 Ω·cm² at 8 days to 424 Ω·cm² at 20 days, indicating a reduced corrosion rate and entry into a stable inhibition stage. The critical failure mechanism is that Cl⁻ preferentially penetrates the surface of the Al₂O₃ passive film, disrupting the metastable state of the coating and thereby creating pathways for corrosive media intrusion. The findings of this study can provide technical support for the safe application of such as-received coatings in non-load-bearing components with heat and corrosion resistance requirements. Full article

This study investigates the influence of nano-alumina (nano-Al₂O₃) on the compressive properties and damage mechanisms of epoxy matrix composites across a wide strain rate range. Composites with varying nano-Al₂O₃ contents (0, 1, 3, 5, 10, 15 wt%) were tested under quasi-static (0.001~0.1 s⁻¹) and dynamic (2500~4800 s⁻¹) conditions using a universal testing machine and a Split Hopkinson Pressure Bar, respectively. The phase, the microstructure, and their effects on macro-mechanical performance and micro-damage were characterized by XRD, SEM, and TEM. Results indicate that the incorporated nano-Al₂O₃ is highly crystalline, single-phase lamellar α-Al₂O₃. Its addition significantly modulates the compressive properties, with effects dependent on both content and strain rate. Under quasi-static compression, yield strength increased monotonically with nano-Al₂O₃ content at 0.1 and 0.01 s⁻¹, reaching a maximum increase of ~9.5% at 15 wt%. However, at 0.001 s⁻¹, optimal strength occurred at 10 wt%, beyond which agglomeration caused degradation. Dynamic tests revealed a positive strain rate effect. The 10 wt% composite exhibited optimal overall performance, combining high peak stress and a stable stress plateau, whereas the 15 wt% sample showed higher peak stress but poor post-peak load-bearing capacity. Microstructural analysis showed that 10 wt% nano-Al₂O₃ dispersed uniformly, enhancing toughness by inhibiting crack propagation via interfacial bonding and microstructural refinement. In contrast, at 15 wt%, particle agglomeration induced interfacial defects, promoting debonding and brittle fracture. This work provides insights into the wide-strain-rate mechanical behavior of nanoparticle-reinforced polymers and supports the design of high-performance, impact-resistant epoxy composites. Full article

In this work, we report the fabrication and characterization of single-film and double-film composite epitaxial garnet structures based on single-crystalline films (SCFs) and bulk single-crystal (SC) scintillators for enhanced α–γ discrimination in mixed radiation fields. These composite scintillators consist of TbAG:Ce and YAG:Ce SCFs grown by liquid-phase epitaxy (LPE) on Czochralski-grown Gd₃Ga_2.5Al_2.5O₁₂ (GAGG:Ce) bulk SC substrates. Single- and double-film architectures were designed to optimize the energy absorption and pulse-shape discrimination (PSD) performance for low-penetrating α-particles and high-energy γ-rays. Energy calibration was performed using different γ-ray sources (⁵⁷Co, ⁵¹Cr, and ¹³⁷Cs), enabling the conversion of detector signals to a calibrated electron-equivalent energy scale (keVee). Integration gates were systematically optimized, yielding maximum figures of merit (FOM) of 1.4 for the GAGG:Ce SC substrate, 1.9 for the single-film composite, and 5.0 for the double-film composite, demonstrating a progressive improvement in α–γ discrimination with increasing structural complexity. Two-dimensional PSD density maps reveal well-separated α and γ events, with the highest separation observed for the double-film composite. These results indicate that the engineering of LPE-grown composites provides tunable scintillation decay profiles, enhanced temporal separation, and increased light yields, making them promising candidates for applications such as mixed radiation field detection, dosimetry, and radiation monitoring. Full article

The NiO/Al₂O₃-CaO, CuO/Al₂O₃-CaO and CoO/Al₂O₃-CaO catalytic systems were investigated for the decomposition of ozone. Each of the three different Al₂O₃-CaO carriers was obtained after treatment of the initial precursor at 1100 °C for 2, 4 and 6 h, respectively, to examine the effect of annealing on support calcination. AAS, XRD, XPS, EPR, SEM and BET were applied for sample characterization. The carrier comprises a mixture of corundum α-Al₂O₃, θ-Al₂O₃ and Ca₃Al₂O₃. The XRD spectra of the active phases of the catalysts show the existence of Co₃O₄, NiO, Ni₂O₃ and CuO. The SEM micrographs reveal spherical particles for the NiO/Al₂O₃–CaO sample. In contrast, the CoO/Al₂O₃–CaO sample exhibits a morphology composed of wool-like fibers and perpendicularly oriented plate-like structures. The CuO/Al₂O₃–CaO sample consists not only of fibrous structures but also of distinct, separated aggregates. The obtained catalysts have highly developed specific surface areas. Their catalytic activity depends on the calcination conditions of the support, and the best results are observed after 2h treatment for all of the investigated samples due to the smaller crystallite size and higher specific surface area. The activity of the investigated catalysts for the ozone decomposition reaction follows the order NiO/Al₂O₃-CaO > CoO/Al₂O₃-CaO > CuO/Al₂O₃-CaO. Full article