Formation Of Layer Research Articles

Electrochemical Production of Tungsten Oxides from Wc-Co Carbide-Type Pseudo-Alloy Waste

Electrochemical research is devoted to the development of a method of processing secondary raw materials containing tungsten in the form of a pseudoalloy of the carbide type WC–Co in sulfate solutions. The target processing products are: powders of tungsten oxides of lower oxidation states, which can be reduced to metallic tungsten with lower costs. Using the methods of linear and cyclic voltammetry, it was established that the selective dissolution of the cobalt component of the pseudoalloy in the studied solutions occurs at potentials more positive than 0.2 V, carbon is removed from the working electrode at a potential > 0.8 V. At the same time, tungsten is oxidized to the higher oxide WO3. It was determined that in sulfuric acid, with an increase in its concentration from 1 to 5 mol∙dm-3, the current density decreases, which is associated with the formation of a solid surface layer of tungsten oxide on the surface of the anode, which passivates the surface. It was established experimentally that when adding 1 mol∙dm-3 of H2SO4 hexamine (C6H12N4) with a concentration of 0.9 mol∙dm-3 to a solution, it is possible to block the process of formation of a passivating film and obtain powders of tungsten oxides of lower oxidation states.

Effect of Ta on selective oxidation behavior and oxide film adhesion of alumina-forming austenitic alloys

The effects of Ta on the selective oxidation behavior and scale adhesion of Fe-45Ni-25Cr-4Al-1.5Nb-0.4C-xTa (x=0.6, 0.9, 1.2, 1.5 wt%) austenitic alloys at high temperature under low oxygen pressure were investigated. The FCC, MC-(Ta, Nb)C, M23C6 and B2-NiAl phases were found in the annealed alloy. Addition of Ta significantly promoted the formation of an external Al2O3 layer and inhibited growth of Cr2O3 and spinel at 850 °C under oxygen pressures of 10−18 atm and 10−24 atm. Similar oxidation behavior was observed in two-step oxidation process (650 °C for 8 hours and 1000 °C for 16 hours). Ta and Nb preferentially segregated at the interface between the oxide scale-matrix as well as grain boundary within the oxide scale during oxidation, and inhibited outward diffusion of Al and Cr. A large oxygen activity gradient was formed in the oxide film, resulting in the formation of columnar grains. Due to a significant decrease in oxygen activity at the front of the reaction, selective oxidation of alumina was promoted. Furthermore, the scratch test technique was used to quantify the adhesion of oxide scales. Peg-like structures formed by Ta and Nb positively influenced the adhesion properties of the oxide scale.

Characterizing sliding wear behavior of A1100/AlFe (p) composites produced via repeated fold-forging and annealing

Abstract Aluminum matrix/aluminum-iron intermetallic composite materials pose challenges in plastic processing due to the susceptibility of hard intermetallic compound particles to fracture. This study introduces a novel fabrication method involving pure iron mesh, hot-dip aluminum plating, and solidification. Through ten consecutive folding, forging, and intermediate annealing cycles, aluminum matrix and iron undergo diffusion, leading to the formation of Fe2Al5 and FeAl3 interface reaction layers, as confirmed by X-ray diffraction analysis. Subsequent forging cycles cause the breakage or detachment of Fe2Al5 and FeAl3 particles from the interface, resulting in the formation of large-sized Fe2Al5 and small-sized Fe2Al5 intermetallic particles. FeAl3 intermetallic particles are observed via microscopic examination. These particles can be uniformly dispersed within the aluminum matrix through plastic flow, enabling the successful fabrication of A1100/Fe2Al5 and AlFe3 composite sheets. Furthermore, the study investigates the impact of intermetallic compound content, sliding speed, and forward load on the dry sliding wear of A1100/FeAl composites. It is found that Fe2Al5 and AlFe3 intermetallic compound particles effectively mitigate adhesive wear, plowing, and oxidative wear of the composites. With an AlFe intermetallic compound content of 4.3 wt.%, the volume wear rate remains low under conditions corresponding to PV = 56.652 (equivalent to a normal load of 19.6 kPa and a sliding speed of 2.87 m s−1).

Development of sustainable flame-retardant bio-based hydrogel composites from hemp/wool nonwovens with chitosan-banana sap hydrogel

Flame retardant (FR) finishing is crucial for developing protective textiles, traditionally relying on halogen, phosphorus, and phosphorus-nitrogen chemistries, which have limitations like toxicity and fabric stiffening. Innovative approaches such as nanotechnology, plasma treatments, and natural resource-based finishes are being explored to achieve sustainable FR textiles. This study presents the development and comprehensive characterization of hydrogel composites made from nonwoven fabrics composed of various hemp/wool blends (70/30, 80/20, and 90/10). The nonwoven fabrics were treated with a chitosan hydrogel incorporating banana sap to enhance their properties. Scanning electron microscope (SEM) examined the surface morphology and structural integrity of the composites, while Fourier transform infrared spectroscopy (FTIR) identified chemical interactions and functional groups. Differential scanning calorimeter (DSC) revealed thermal properties, water absorbency tests demonstrated hydrophilicity, mechanical testing assessed tensile strength, and vertical flammability tests evaluated fire resistance. SEM and FTIR revealed a successful coating of chitosan hydrogel with banana sap inclusions onto the hemp/wool nonwoven fabric, forming a composite structure. DSC analysis suggests higher chitosan content and hemp fiber ratio (like 70/30) lead to increased thermal stability of hydrogel composites. Higher chitosan concentrations in the hydrogel significantly improve the flame-retardant properties of hemp/wool nonwoven fabrics by reducing char length and enhancing protective char layer formation, with banana sap further promoting charring. These results indicate that the developed composite can be effectively used in flame-retardant textiles.

Effects of suspended titanium dioxide (TiO2) nanoparticles on cake layer formation in submerged anaerobic membrane bioreactor (AnMBR) for landfill leachate treatment (LFL)

In recent years, TiO2 NPs have attracted great attention among the semiconductors because of stability, commercial availability, and ease of preparation. For this reason, NPs are widely used in wastewater treatment and membrane bioreactor (MBRs) In this study, the effect of titanium dioxide (TiO2) nanoparticle material was investigated on both the landfill leachate (LFL) treatment and membrane fouling performance. The system performance was evaluated for under varying TiO2 concentrations (50–300 mg/L TiO2), constant HRT (24 h), and constant backwashing (5 min)-relaxing (0.5 min) in AnMBR. The optimum conditions were determined as 300 mg/L TiO2 and the corresponding to COD, Color, TOC and TN removal efficiencies were observed as 55 %, 23 %, 22 %, 30 %, respectively. The best membrane performance was observed at 300 mg/L TiO2 corresponding to membrane fouling rate as 0.01 mbar/min. TiO2 addition significantly mitigated membrane fouling (75 % decrease) for AnMBR. Bacteroidetes, Firmicutes and Proteobacteria have been observed to be the dominant species in LFL and MBRs. The bacterial species responsible for membrane fouling were determined as Alphaproteobacteria, Sphingobacteria and Flavobacteria. The addition of TiO2 was determined membrane fouling decreased in AnMBR. As a result of TiO2 NPs were observed to thin the cake layer and postpone membrane fouling and filtration.

Effect of the gas layer evolution on electrolytic plasma polishing of stainless steel

In recent years, electrolytic plasma polishing technology has attracted wide attention due to its advantages of shape adaptability, high efficiency, better precision, environmental friendliness, and non-contact polishing. However, the lack of research on the evolution mechanism of the gas layer at the anode interface restricts the improvement of the material removal mechanism and the regulation of the polishing effect. Firstly, the thermodynamic conditions of gas layer formation were analyzed based on the Clapeyron-Clausius equation, and the key parameters affecting the gas layer were identified. Secondly, the laws of voltage and electrolyte temperature on the dynamic evolution of the gas layer and its polishing effect were revealed. Additionally, the influence of the gas layer on the voltage-current characteristics was also investigated by analyzing the experimental phenomena. The results indicate that the optimal polishing effect is achieved at a voltage level of 300 V resulting in a decrease in Ra from 0.451 μm to 0.076 μm. Similarly, superior polishing results are obtained when the electrolyte temperature is 80 °C, with a decrease in Ra from 0.451 μm to 0.075 μm. This study provides theoretical guidance for the further development and application of electrolytic plasma polishing technology.

Alkaline-Metal Cations Affect Pt Deactivation for the Electrooxidation of Small Organic Molecules by Affecting the Formation of Inactive Pt Oxide.

The activity of Pt for the electro-oxidation of several organic molecules changes with the cation of the electrolyte. It has been proposed that the underlying reason behind that effect is the so-called noncovalent interactions between the hydrated cations and adsorbed OH (OHad). However, there is a lack of spectroscopic evidence for this phenomenon, resulting in an incomplete understanding at the microscopic level of these electrochemical processes. Herein, we explore the electro-oxidation of glycerol (EOG) on platinum (Pt) in LiOH, NaOH and KOH using in situ surface-enhanced infrared absorption spectroscopy in the attenuated total reflectance mode (ATR-SEIRAS) and in situ X-ray absorption spectroscopy (XAS). Our results show that the electrolyte cation influences the rate and potential at which adsorbed CO (COad), a catalytic poison, is formed and oxidized. We attribute this to the cation-dependent stability of oxygenated species on the metallic Pt surface and the different intensities of the electric field at the electrode/electrolyte interface. We also demonstrate that the formation of an inactive Pt oxide layer is indirectly also cation-dependent: the formation of this layer is triggered by the cation-dependent oxidative removal of reaction intermediates (for instance, CO). This phenomenon explains the well-known cation-induced differences in the voltammetric profiles, of not just glycerol, but generally of alcohols and polyols.

Fracture propagation behavior via multi-cluster fracturing in sandstone-shale interbedded reservoirs

Initiation and propagation of fractures in multi-layered formations has been a topic of interest for the efficient utilization of hydrocarbon resources. Although there is a reasonable body of knowledge to facilitate the design and development of hydraulic fracture, the understanding of initiation and propagation of fracture clusters in layered formation is limited. This paper discusses the findings from controlled laboratory experiments and numerical modeling to understand the initiation and propagation of hydraulic fracturing operations. True triaxial tests were carried out on samples extracted from outcrop representative of Lianggaoshan formation in China. It was noted that the differential stress between the layers is critical for the initiation and propagation of multiple fracture. It was also noted that the viscosity of the fracturing fluid influences the propagation of fractures across lamina and interfaces. The intermediatory response of rocks due to the injected fluid was studied through numerical modeling of the physical process using modified cohesive zone model, which was then validated by the output from the laboratory experiments. It was noted that the increase in the fracture cluster has the potential to constrain the extent of fracture propagation whereas decrease in the cluster size increases the extent of fracture propagation. Compared to sandstone, the fracture height in shale is 30% lower. For sandstone, early-stage fracture flow distribution stabilizes more quickly, and higher fluid pressure within fractures significantly increases fracture height and effective stimulation volume.

Enhanced hot corrosion resistance of AlCoCrFeNi2.1 high entropy alloy coatings by extreme high-speed laser cladding

Extreme high-speed laser cladding (EHLC) and multiple laser remelting (EHLC-MR) are used to improve hot corrosion resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) coatings by refining their microstructures, introducing low angle grain boundaries (LAGBs) and high densities of dislocations as well as higher compressive residual stresses (CRSs) in the coatings. The experimental results show that finer microstructure, more LAGBs and high densities of dislocations are beneficial to increase Al2O3 nucleation sites and promote the uniform formation of the oxide layer on the coating surface. On the other hand, higher CRSs suppress the initiation and propagation of cracks as well as enhance the adhesion between the oxide layer and the substrate. Thus the hot corrosion resistance of the EHEA coatings under a molten salt of 75% Na2SO4 + 25% NaCl at 900°C is improved significantly. These novel results provide effective approach for designing elevated-temperature materials.

Alpha-case promotes fatigue cracks initiation from the surface in heat treated Ti-6Al-4V fabricated by Laser Powder Bed Fusion

This research investigates the effect of the formation of an oxygen-stabilised titanium alpha layer – called alpha-case at the surface – on the fatigue properties of Ti-6Al-4V (Ti64) alloy components produced by Laser Powder Bed Fusion (L-PBF). Three post processing heat treatments with different controlled atmospheres were carried out on samples with as-built surfaces to evaluate how differences in alpha-case layer thickness and hardness affect the material’s susceptibility to surface embrittlement and its overall fatigue performance. The investigation includes bulk and subsurface microstructural analysis, surface characterisation by X-ray computed tomography (XCT), and fatigue testing. Key findings show that alpha-case layers can reduce the fatigue resistance of L-PBF fabricated Ti64. The presence of a 70±3 µm thick alpha-case layer was found to promote crack initiation. This is emphasised by a higher density of initiated cracks, thus leading to a reduction in fatigue life. Conversely, thinner alpha-case layers were found to have a reduced impact on the fatigue performance, highlighting the critical role of post processing heat treatments in modulating the fatigue resistance of the material. The use of XCT to characterise the surfaces of the specimens in 3D confirms that fatigue cracks primarily initiate at surface notches, highlighting the predominance of as-built surfaces over microstructure in determining the fatigue resistance of L-PBF Ti64 components.

Assessment of ethanolic extract of Dittrichia viscosa from Kardoussa Douar region of Taza in Morocco as antioxidant and green inhibitor for carbon steel corrosion in acidic medium

This study targeted evaluating the anticorrosive and antioxidative characteristics of Dittrichia viscosa (ZS-OH) extract. ZS-OH was first extracted by deploying a soxhlet and characterized by chromatographic analysis (GC/MS). In addition, a quantitative assessment of the total phenolic (TPC) and flavonoids (FC) content of the ZS-OH extract, as well as phytochemical analyses, were carried out. Antioxidant testing was conducted using the bioassay: 2,2-diphenyl-1-picrylhydrazyl (DPPH). The ability of ZS-OH extract to stymie the corrosion of carbon steel in 1.0 M HCl was considered through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). ZS-OH extract yield was 4.73 %, and GC-MS revealed 32 distinct chemicals. Neryl isovalerate (29.8 %), 1,10-di-epi-Cubenol (25.4 %), and 2,5-dimethoxy-p-cymene (11.6 %) made up the majority of the ZS-OH extract. The electrochemical results reveal that the ZS-OH extract acts as a mixed-type with an inhibition efficiency of up to 96.8 % at 500 ppm under 303 K. Surface analyses using SEM/EDS confirmed the formation of the protective layer of ZS-OH extract molecules on the C-S surface. The three major components are fully optimized in the DFT through the B3LYP functional and 6–311++G(d,p) basis sets. Molecular dynamics simulation data show the molecules of ZS-OH extract oriented beneficially on metal surfaces, providing a high surface coverage, and thus, a high inhibition performance.

S@FeS2 Core-Shell Cathode Nanomaterial for Preventing Polysulfides Shuttling and Forming Solid Electrolyte Interphase in High-Rate Li-S Batteries.

Lithium-sulfur (Li-S) battery is a potential next-generation energy storage technology over lithium-ion batteries for high capacity, cost-effective, and environmentally friendly solutions. However, several issues including polysulfides shuttle, low conductivity and limited rate-capability have hampered its practical application. Herein, a new class of cathode active material with perfect core-shell structure is reported, in which sulfur is fully encapsulated by conductivity-enhancing FeS2 (named as S@FeS2), for high-rate application. Surface-stabilized S@FeS2 cathode exhibits a stable cycling performance under 2 - 20 times higher rates (1-2 C, charged in 30-60min) than standard rates (e.g., 0.1-0.5C, charged in 2-10h), without polysulfides shuttle event. Surface analysis results reveal the unprecedented formation of a stable solid electrolyte interphase (SEI) layer on S@FeS2 cathode, which is distinguished from other sulfur-based cathodes that are not able to form the SEI layer. The data suggest that the prevention of polysulfides shuttling is owing to the surface protection effect of FeS2 shell and the SEI layer formation overlying core-shell S@FeS2. This unique and potential material concept proposed in the present study will give insight into designing a prospective fast charging Li-S battery.

Study on surface chemical composition of argon atomized superalloy powder based on TOF-SIMS

Nickel-based powder metallurgy superalloys have been extensively employed in aerospace industry because of their superior performance. However, severe defects can be formed in primary particle boundaries (PPB) during manufacturing process of superalloys, significantly deteriorating their practical performance. This study comprehensively investigates the surface structure, elemental distribution, and chemical state of FGH96 superalloy powder via several advanced surface characterization techniques. The results indicate that the strong binding affinity between metal elements (e.g., Al, Cr, Ti) and O/H elements contributes to the formation of an oxide layer in both surface and interval areas, providing an essential chemical basis for the development of PPB. Furthermore, Ti and Al exhibit the highest binding strength with O, which may form stable oxides. Hopefully, these findings will facilitate the emergence of PPB-free superalloys with improved performance.

POST-EL-NIÑO WEAKENING OF COASTAL UPWELLING AND ITS ECOLOGICAL IMPACTS IN THE SOUTH-CENTRAL VIET NAM REGION

Upwelling that occurs in the summer offshore of South-Central Viet Nam in the South China Sea (SCS) also known as the East Viet Nam Sea (EVS), is one of the region’s key dynamic processes. The weakening of upwelling phenomena during post-El-Niño events and their ecological responses were studied based on a reanalysis dataset derived from the HYCOM/NCODA system, coupled with a local Finite Element Model (FEM) and observed data. Long-term warming, along with orographic and wind factors, play significant roles in the formation and weakening of upwelling phenomena during normal and post-El-Niño episodes, respectively. The weakening of upwelling during post-El-Niño periods is reflected by: Extreme weakening of wind forcing and Ekman pumping; a northward shift of the cold-saline tongue and current dipole, with a limited eastward extent; dominance of northward circulation in the surface layer and westward circulation in deeper layers; and the formation of a homogeneous surface thermohaline layer of about 50 meters thick, with a thermo-halocline layer at 50-60 meters depth. These abrupt changes strongly influenced the ecological characteristics of the upwelling area. Coral bleaching during the summers of 2010 and 2016, as well as anomalous distributions of chlorophyll-a (Chl-a) in the surface layer in 1998, 2003, 2010, and 2016, were concrete indicators of the ecological responses of Viet Nam's coastal upwelling waters in post-El-Niño years. Detailed intra-seasonal variations of temperature during the summer showed a warming of the waters, leading to coral bleaching and abnormal Chl-a levels during post-El-Niño years. Organisms in this region struggled to adapt to these rapid environmental changes, leading to a potential reduction in living resources.

Mussel-inspired polydopamine (PDA)-grafted 2D-Ti3C2 MXene nanosheets tailored ZnAl-layered double hydroxides (LDH); Toward designing a smart self-healing epoxy composite coating

The constant challenge of corrosion significantly compromises the durability and functionality of metal substrates, propelling the demand for advanced protective solutions. This study introduces a novel smart epoxy coating system modified with a three-component nanocomposite integrating polydopamine (PDA)-modified Ti3C2 MXene with ZnAl-layered double hydroxides (LDH), intercalated with phosphate (P) and glutamate (Gl) ions as corrosion inhibitors. The innovative approach leverages the synergistic impacts of barrier protection, ion exchangeability, and self-healing capabilities to offer superior anti-corrosion performance. In the solution phase, the EIS results revealed a notable increase in resistance values, with MPLG samples exhibiting a 2.45-fold and MPLP samples a 2.17-fold enhancement compared to the blank specimen after 96 h of immersion. Furthermore, the data obtained from EIS demonstrated a significant enhancement in the barrier effects of the epoxy coating upon the addition of MPLG and MPLP. This enhancement was evidenced by a significant increase in the impedance values, which were observed to be 103-fold higher following a prolonged immersion period of 140 days. The self-healing properties, confirmed through EIS, FE-SEM, and EDX/Mapping analyses, indicated the formation of a stable corrosion-protective layer over the damaged areas, thus providing active protection. Adhesion assessments further underscored the coatings' durability, with MPLG and MPLP samples demonstrating minimal delamination. Collectively, these findings emphasize the potential of the proposed PDA-modified MXene@ZnAl-LDH nanocomposite as a multifaceted solution to corrosion challenges, promising significant advancements in the longevity and reliability of coated metal surfaces.

Sukralfat as a Therapy for Reducing Itching and Repairing the Skin Barrier: A Systematic Review

Sucralate is an aluminum salt from sucrose octasulfate that is known for its anti-ulcer activity, mucosal protection, and anti-mucositis potential. Recently, sucralfat has been used topically for the healing of various epithelial wounds, including ulcers, inflammatory dermatitis, mucositis, and burns. This systematic review aimed to evaluate the effectiveness of sucralfat as a topical therapy in reducing itching (pruritus) and improving the skin barrier. The analysis method used is Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA). A literature search was conducted on studies from 2004 to 2024 using keywords such as "sucralfate", "pruritus", "dermatitis", and "skin barrier" on PubMed, ProQuest, Science Direct, and Scopus databases. Inclusion criteria include topic relevance, research design, human subjects, and United Kingdom-speaking studies. Of the 141 articles found, 7 articles met the inclusion criteria. These studies involved a total of 605 subjects from different countries and used clinical trial methods and randomized controlled trials. The results showed that topical sucralfat was effective in reducing itching and improving the skin barrier in various skin conditions such as diaper dermatitis, chronic ulcers, and postoperative wounds. Sukralfat shows great potential in wound healing and skin barrier repair through the mechanism of protective layer formation, increased expression of epidermal growth factors, and anti-inflammatory properties. This effect indirectly helps reduce pruritus which often occurs due to damage to the skin barrier. Topical succulthate is effective in reducing itching and repairing the skin barrier, making it a promising therapy for a variety of inflammatory and ulcerative skin conditions.

Electrochemical Kinetics of LiFePO4 Cathode Material in Non-flammable Inorganic Liquid Electrolyte.

We unveil the fundamental insights of electrochemical kinetics of LFP cathode material and the passivation layer formation in the SO2-based non-flammable inorganic liquid electrolyte (IE). The influence of temperature and electrochemical potential cutoff in the electrochemical activity of LFP cathode and IE is disclosed. Furthermore, the materials compatibility, structural and chemical stability of LFP in IE is demonstrated using very slow galvanostatic cycling in combination with LiFePO4||Li0.1FePO4 symmetric cells. The lithium storage performance of LFP half-cell using inorganic electrolyte is presented with the optimum voltage window. LFP half-cells exhibit discharge capacities of 147, 111, and 75 mAh/g at 1, 4, 8 C rates, respectively, with coulombic efficiencies of ~99.98 %. The electrochemical behavior and mechanism of LFP||Graphite cell in IE is investigated while concurrently tracking the electrochemical potentials of LFP and Graphite half-cell.

Impact of plasma treatment of Au electrodes on response of EIS biosensors used in aquaculture pathogen detection

This study examines the effect of plasma treatment on gold electrodes used in construction of biosensors. Plasma treatment aims to improve the adhesion of bioreceptor layers, enhancing sensor performance. Gold substrates were exposed to plasma for different durations, and their reactivity was analyzed using electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Results show that plasma treatment significantly enhances the hydrophilicity of gold surfaces, leading to better formation of bioreceptor layer. Optimal treatment duration was found to be around 60 s, beyond which improvements in impedance values diminished. Plasma-treated electrodes displayed superior bioreceptor adhesion without altering surface topography. In conclusion, plasma treatment improves biosensor performance by enhancing bioreceptor layer adhesion. Integrating this process into biosensor production can lead to more efficient and reliable pathogen detection in aquaculture, promoting healthier aquatic environments and sustainable food production.

Dry sliding wear characteristics of hybrid aluminum alloy with nano-fly ash and nano-yttrium oxide

Aluminum alloys feature impressive levels of strength, ductility, castability, wear resistance, and corrosion resistance, making them highly advantageous for the aviation and automotive industries. This study investigates the dry wear performance of hybrid nanocomposites (HNCs) produced using Al6061 as the matrix, with nano-fly ash (FA) and nano-yttrium oxide (Y2O3) as reinforcing agents, utilizing the stir-casting method. The weight percentage (wt-%) of FA was fixed at 4 wt-%, while the Y2O3 varied from 1 wt-% to 3 wt-%. The specimens were prepared following ASTM-G99 standards and tested using a pin-on-disc apparatus with an E31 steel disc under four different loads: 10 N, 20 N, 30 N, and 40 N. It has been observed that wear rate has been increased with the increase in the applied load. The maximum wear rate has been recorded for the base Al6061 alloy as 5.63 × 10−4 mm3/N-m at 40 N load due to its lower wear resistance and less hardness value. The addition of reinforcement particles in the base alloy results in the grain refinement and improvement in the load-bearing capacity. It has been found that at 40 N load, the Al-6061 alloy reinforced with (4 wt-% FA + 3 wt-% Y2O3) is 56.83% superior in terms of wear resistance (2.43 × 10−4 mm3/N-m) as compared to Al6061 base alloy. The hybrid nano-composite containing 4 wt-% FA + 3 wt-% Y2O3 showed the highest value of microhardness as 123.2 HV, which is 136% higher than that of base alloy due to the higher load-bearing characteristics of the reinforcement particles. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) have been employed to analyze both unworn and worn surfaces, revealing uniform dispersion of reinforcement particles, the formation of an oxide layer, micro-pitting, wear debris, and material delamination. Grain refinement has been examined using the line intercept method (ASTM E1382-97), and X-ray diffraction (XRD) confirmed the elemental composition of the nano-reinforcements.

Microstructure characterization of plasma electrolytic oxidation coating on Hf-Nb-Ta-Zr high entropy alloy

The morphology, composition, and microstructure of plasma electrolytic oxidation (PEO) coating on Hf-Nb-Ta-Zr high entropy alloy (HEA) were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, glow discharge optical emission spectroscopy (GDOES) and transmission electron microscopy (TEM). The formation mechanism of PEO coating was analyzed. It was found that a dense PEO coating of ∼4 μm thick on the HEA surface was formed, which consisted of tetragonal and monoclinic ZrO2 phases, tetragonal and monoclinic HfO2 phases, Nb2O5 and Ta2O5 phases. The PEO coating from the alloy substrate to the surface contained five distinctive layers: amorphous barrier layer, nanocrystalline layer, columnar grain layer, amorphous outer layer, and top porous layer. Their formation was ascribed to the different cooling rates of the melt in the different depths of the discharge channel across the coating. Meanwhile, the formation of an amorphous barrier layer near the HEA substrate was also related to the mutual migration and diffusion of Hf4+, Nb5+, Ta5+, Zr4+ and O2− besides the rapid cooling of melt in the bottom of the discharge channel. The columnar grains of ∼70 nm wide were mainly composed of the monoclinic ZrO2 and monoclinic HfO2 phases, but both the amorphous layers enrich the Ta and Nb elements. It was believed that the high-content Ta and Nb in the HEA enhanced the formation of the amorphous layers.