Introduction and Objectives: The development of stable cathode materials for intermediate-temperature solid oxide fuel cells remains a significant challenge. The perovskite oxide La1-xCaxFeO3-δ is considered a promising cathode candidate due to its favorable mixed ionic–electronic conductivity and stability, and the possibility of tailoring its structural properties. However, the synthesis of single-phase La1-xCaxFeO3-δ typically requires high calcination temperatures and long processing times. The present study aims to synthesize phase-pure La1-xCaxFeO3-δ using a co-precipitation method at the lowest possible temperature and shortest processing time.Materials and Methods: La0.65Ca0.35FeO3-δ cathode powder was synthesized via a co-precipitation route and subsequently calcined at various temperatures after drying. The optimized powder was then employed in the fabrication of symmetric fuel cells deposited on Yttria-stabilized Zirconia electrolytes with a Gadolinium-Doped Ceria buffer layer.Results: Simultaneous thermal analysis and X-ray diffraction analyses revealed complete formation of the orthorhombic perovskite phase (Pnma) at approximately 700 °C. Fourier transform infrared spectroscopy confirmed the complete removal of nitrate group and the formation of metal–oxygen bonds. Field emission scanning electron microscopy images showed a nanostructured morphology with an average particle size of 26.57 nm. The optimized sample exhibited a thermal expansion coefficient of 11.3308×10⁻6 °C⁻¹, which is compatible with common electrolytes. Electrochemical impedance spectroscopy showed the minimum values for the ohmic and polarization resistances to be 1.439 Ω·cm² and 0.242 Ω·cm², respectively, at 800 °C.Conclusion: The co-precipitation method was found to be effective for synthesizing phase-pure La0.65Ca0.35FeO3-δ with a desirable nanostructure and appropriate electrochemical properties, thus serving as an efficient and cost-effective alternative for the preparation of solid oxide fuel cells catalyst.
Introduction and Objectives: Keratin coatings have attracted attention as a novel solution for controlling the rate of substrate degradation and corrosion and enhancing bone regeneration due to their unique properties. The aim of the present study is to develop a keratin coating on magnesium alloy in order to control its corrosion behavior.Materials and Methods: In this study, keratin was extracted from pigeon feathers following the protocol described in previous research. To enhance substrate adhesion, the magnesium alloy was alkalized prior to coating. The morphology and thickness of the keratin coating were optimized by varying the electrospray duration (30, 60, 90, and 120 minutes). Fourier-transform infrared spectroscopy (FTIR) was employed to confirm the successful extraction of keratin, while potentiodynamic polarization tests were conducted to assess the corrosion resistance of the coated samples.Results: The infrared spectroscopy results revealed characteristic peptide bonds corresponding to amide I (1635 cm⁻¹), amide II (1531 cm⁻¹), and amide III (1238 cm⁻¹). Furthermore, the water contact angle of samples coated with keratin for 30, 60, 90, and 120 minutes decreased progressively to 54 ± 1°, 49 ± 2°, 45 ± 2°, and 41 ± 0.5°, respectively, indicating enhanced surface wettability.Conclusion: The results of this study demonstrate modifications in surface properties such as roughness and wettability, along with a significant enhancement in the corrosion resistance of AZ91 alloy coated with keratin. This improvement is attributed to the formation of an effective physical barrier and the excellent biocompatibility of keratin, suggesting its potential for broad applications in the medical field.
Introduction and Objectives: Detecting the CD8⁺ T cell biomarker—a key indicator of immunological diseases—is often slow with current methods. This research aims to develop a sensitive, accurate, and easy-to-use electrochemical biosensor, utilizing reduced graphene oxide and polypyrrole nanocomposite, for on-site, sensitive, accurate, and rapid detection of CD8⁺ T cells. Materials and Methods: The polypyrrole/reduced graphene oxide composite was deposited onto the sensor's working electrode using cyclic voltammetry with 15, 20, and 25 cycles, corresponding to sample codes A15, A20, and A25. To prepare the sample containing the polypyrrole and graphene oxide composite with the selected number of cycles under a UV lamp (sample code B20), the same procedure was repeated, followed by characterization of the samples. Antibody immobilization was then performed on the developed electrode, and sensor performance was assessed using differential pulse voltammetry. Results: FESEM imaging revealed that the sample A20 had a more uniform and porous surface morphology compared to the sample B20. According to the differential pulse voltammetry results, an increase in the concentration of CD8⁺ T cells led to a decrease in current intensity. Based on the calibration curve, the detection limit was determined to be seven cells.ml-1, indicating the high sensitivity of the sensor in identifying CD8⁺ T cells.Conclusion: Sample A20 was identified as the optimal structure for application in electrochemical biosensors based on Ppy-rGo composite to detect CD8+ T cells.
Introduction and Objectives: In this study, the microstructural and mechanical properties of dissimilar resistance spot welds between DP590 and HSLA440 steels were investigated, with a focus on the effect of welding current. Materials and Methods: For this purpose, steel sheets were prepared in accordance with AWS D1.1 standard. Welding was performed using currents ranging from 7 to 11 kA (in 1 kA increments), followed by mechanical testing and characterization. Tensile shear tests were conducted at a crosshead speed of 1 mm/min, and hardness tests were carried out for the 8 and 10 kA welds. Furthermore, fracture surface and weld microstructure analyses were performed using optical and scanning electron microscopy. Results: Weld nugget was mainly consisted of lath martensite; its volume fraction increased with current and decreased toward base metal. In DP590, the supercritical and intercritical regions were martensitic and the subcritical region was tempered. In HSLA440, the supercritical regions showed martensite, the intercritical regions showed a combination of martensite and ferrite, and the subcritical region showed grain growth.Tensile strength enhanced from 10.84 kN (for 7 kA) to 24.34 kN (for 10 kA). Fracture mode shifted from interfacial to pull-out above 9 kA. Hardness increased with current, peaking at 430 HV (10 kA).Conclusion: An increase in welding current caused to increase in nugget size and peak load. Also, softening was more pronounced on the HSLA440 side. The sample welded at a current of 10 kA with a tensile failure mode and maximum strength, hardness, and elongation was the optimal sample.
Introduction and Objectives: Zinc oxide nanoparticles were synthesized as ultraviolet absorbers using green tea extract as a reducing and stabilizing agent.Materials and Methods: Green tea extract, which was obtained by brewing 10 g of green tea in 100 ml of distilled water at a temperature of 60 to 80 °C, was added dropwise to a zinc acetate solution, and then a diluted oxalic acid solution was added dropwise to it. The mixture was stirred at 75 °C for 2 hours to precipitate at pH 7. The resulting powder was dried in an oven for 12 hours and heat-treated in an electrical furnace at 450 °C.Results: X-ray diffraction and scanning electron microscope analyses showed that the synthesized nanoparticles have a porous structure with an average crystallite size of about 24 nm. Fourier Transform Infrared spectroscopy confirmed the presence of O–H, C–H, C=O and C–O surface active groups. Calcination of the resulting powder at 450°C resulted in an increase in the intensity of the Zn–O bond, improved crystallinity and enhanced ultraviolet absorption. Ultraviolet–visible spectroscopy of this sample revealed an absorption peak at 370 nm, and Energy Dispersive spectroscopy analysis confirmed the high purity of the final product.Conclusion: This study declares that green tea extract can be used as a natural and biocompatible agent in the synthesis of zinc oxide nanoparticles with desirable morphological and optical properties. The produced nanoparticles absorb ultraviolet radiation efficiently.
Introduction and Objectives: One effective approach for enhancing the mechanical properties of metal matrix composites is the design of architected layered heterogeneous structures. Hence, the present study aimed to develop aluminum matrix hybrid composites reinforced with SiC ceramic particles and iron-based amorphous particles, featuring a heterogeneous layered architecture and to investigate their mechanical properties.Materials and Methods: The heterogeneous structure comprised alternating layers of pure aluminum and composite material with varying thicknesses, fabricated via powder metallurgy using spark plasma sintering (SPS). The microstructural and phase characteristics of the composites were investigated using scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffraction (XRD). The relationship between microstructure and mechanical properties was subsequently analyzed.Results: Microstructural analyses, including porosity evaluation and density measurements, demonstrated enhanced densification during sintering with increasing pure aluminum layer thickness. In addition, the distribution of reinforcement particles was improved by increasing the volume fraction of the pure aluminum layers relative to the composite layers. Phase analysis of all sintered samples confirmed the preservation of the amorphous nature of the iron-based reinforcement particles and revealed no evidence of interfacial reaction products at the reinforcement–matrix interfaces. Mechanical experiments showed a favorable combination of high strength and ductility, with a compressive strength of up to 191 MPa and a fracture strain of 20% in samples with a higher volume fraction of composite layers. Furthermore, increased ductility was observed with a higher volume fraction of pure aluminum layers.Conclusion: The introduction of a layered heterogeneous architecture in the hybrid composite, through modification of consolidation behavior and reinforcement particle distribution, resulted in superior mechanical properties compared to those of the homogeneous composite.
Introduction and Objectives: Ceramics based calcium silicate such as Akermanite (Ca2MgSi2O7) are suitable bioactive materials for bone tissue engineering applications. However, they suffer from poor mechanical properties. So, additives like graphene or its derivatives are used. In this regard, in this study, reduced graphene oxide (0.5%, 1%, and 1.5% by weight) has been employed as a reinforcement. Materials and Methods: The mixture of raw materials (akermanite and reduced graphene oxide to the desired ratio) went through various preparation stages followed by sintering process and finally, the sintered samples were characterized.Results: By increasing the weight percentage of reduced graphene oxide from zero (control sample) to 1.5 wt. %, a decrease in relative density from 94.9% to 89.3% and a reduction in compressive strength from 13 to 8 Mpa was observed. Toughness increased from 1.9 for the control sample to 4.2 for the 1 wt.% sample, it decreased to 2.7 MPa.m1/2 for a 1.5 wt.% sample, though. Similarly, the hardness increased from 435 for the control sample to 588 Vickers for the 1 wt.% sample, and decreased to 308 Vickers for the 1.5 wt.% sample.Conclusion: Among the composite specimens, the most homogeneous microstructure was related to the 1 wt.% sample with the highest mechanical properties (toughness and hardness). Graphene oxide not only does not prevent the formation of the apatite layer, but also encourages the formation of dense and fine apatite deposits on the surface of the composite sample.
Introduction and Objectives: Considering the increasing need for biocompatible materials in medicine, designing hydrogels with optimal mechanical and biological properties has become important. Polymeric hydrogels, such as polyvinyl alcohol, are widely used in medical applications due to their biocompatibility, high swelling capacity, and mechanical properties similar to those of body tissues. Incorporating nanoparticles, such as zinc oxide, can further enhance their properties. In this study, for the first time, the effect of different physical crosslinking methods and the addition of zinc oxide nanoparticles on the mechanical and biological properties of poly(vinyl alcohol) hydrogels was investigated.Materials and Methods: Nanocomposite hydrogels containing different percentages of zinc oxide nanoparticles were prepared by two different physical methods, with and without a cross-linking agent. A combination of these two methods was also used. The morphology and structure of the hydrogels were characterized using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The mechanical properties and biocompatibility were evaluated by tensile testing and cell viability measurement for biological applications.Results: The hydrogel containing 15% zinc oxide nanoparticles, prepared with the cross-linking agent and the freeze–thaw method, showed the highest tensile strength (37.5 MPa), elongation at break (55%), storage modulus (23 MPa), and cell viability (70%). The microscopic images and spectroscopy results indicated the formation of a strong hydrogel network and strong hydrogen bonds, which improved the mechanical and biological properties. In addition, increasing the percentage of zinc oxide nanoparticles enhanced the biocompatibility of the samples.Conclusion: A suitable combination of the preparation method and the amount of zinc oxide nanoparticles can improve the mechanical and biological properties of poly(vinyl alcohol) hydrogels and make these materials suitable for medical and biological applications.
Introduction and Objectives: The use of bioactive glass in therapeutic applications is a promising and developing field of research to improve the treatment process, made these biomaterials one of the reliable options in tissue engineering. In this study, the effect of strontium oxide contamination in the chemical composition of bioactive glass 70S on its structural and biological properties was examined. Materials and Methods: In this study, the structure of bioactive glass 70SiO2-(30-x)CaO-xSrO (x= 0 and 5 mol.%) synthesized by melt-quenching method was simulated through molecular dynamics and lAMMPS software. Results: According to the results of the pair distribution function and the angle distribution function, the average length of the Si-O, Si-BO, and Si-NBO bonds was reported to be 1.61, 1.62, and 1.58 (Å) respectively, and the angle size of the Si-O-Si and O-Si-O bonds was 147-151° and 109°, respectively. The distribution of bridging oxygens and non-bridging oxygens in the BG-S5 sample also decreased and increased by 0.42% and 0.21%, respectively compared to the BG-S10 sample. In addition, an increase in the pH of the simulated body fluid was reported by the day of seven immersion due to the release of ions from the glass surface, and an improvement of 17.26 % in the growth and proliferation of MC3T3-E1 cells in the BG-S5 sample compared to the BG-S10 sample on the day of seven cultures was confirmed (****p<0.0001). Conclusion: Molecular dynamics simulation is a powerful tool in order to accurately predict the structural properties of bioactive glass before synthesis in vitro conditions, and the BG-S5 sample was proposed in bone tissue engineering due to its optimal bioavailability.
Introduction and Objectives: The aim of this research is to implement the Miedema model in the thermodynamic analysis of dissolution in titanium-based alloys. Materials and Methods: In this regard, various components of the enthalpy of dissolution, including chemical enthalpy, elastic enthalpy, and structural enthalpy, along with the component related to the entropy of the state, were investigated for several binary titanium-transition elements alloys, and the Ω characteristic, which is a component consisting of the enthalpy of dissolution, entropy of the state, and average melting temperature, was introduced. Results: The results showed that the use of thermodynamic analyses relying on the Ω characteristic is well able to predict the solubility range in titanium-based alloys containing transition elements. It was found that the solubility range in titanium-based alloys occurs when the component Ω≤1. Conclusion: Finally, the proposed component was implemented for the ternary Ti-Zr-Cu alloys. It was found that the component with Ω≤1 is capable of well predicting the dissolution behavior in the studied alloy.
Introduction and Objectives: This study investigated the effect of silver nanoparticles (AgNPs) in MAGIC-f polymer gel on the absorbed dose of gamma rays from americium-241 (241Am) and cesium-137 (137Cs) sources. The main objectives were to evaluate changes in the transmission coefficient, linear and mass attenuation coefficients, linear energy absorption, and absorbed dose for different concentrations of AgNPs, and to compare the experimental behavior with theoretical results.Materials and Methods: MAGIC-f gel samples were prepared with 14 different concentrations of AgNPs (ranging from 0 to 1.22% by weight). After polymerization, the transmission spectra of the gels, both with and without nanoparticles, using a NaI(Tl) detector under irradiation from 241Am (59 keV) and 137Cs (662 keV) gamma-ray sources. Following background subtraction, the spectral data were used to calculate the target parameters.Results: Experimental results showed that adding AgNPs reduced the transmission coefficient: for 241Am, it decreased from 0.895 (pure gel) to 0.810 (gel with 1.04 wt. % AgNPs), and for 137Cs, from 0.891 to 0.859. Furthermore, the linear and mass attenuation coefficients for both gamma energies exhibited an increasing trend, and the absorbed dose parameter showed a measurable increase. Theoretical calculations indicated a decrease in the transmission coefficient for 241Am from 0.745 (pure gel) to 0.670. In contrast, this parameter remained nearly constant for 137Cs in the theoretical data.Conclusion: The findings indicate that silver nanoparticles, particularly at lower gamma energies, enhance the attenuation and absorption of gamma rays, thereby increasing the absorbed dose in the MAGIC-f polymer gel.
Introduction and Objectives: The growing demand for high-energy batteries has accelerated research on high-capacity lithium-rich cathodes. However, the aforementioned cathodes suffer from several drawbacks such as low electronic and ionic conductivity, which subsequently have adverse impact on their electrochemical performance. To overcome these issues, doping with metal ions is an effective strategy. This study aims to investigate the effects of Zn and Cd doping on structural and electrochemical behaviour of Li[Li₀.₂₀Mn₀.₅₄Ni₀.₁₃Co₀.₁₃]O₂ (LMNCO) cathode. Materials and Methods: Pure LMNCO cathodes and doped with Zn and Cd were synthesized by sol-gel method. The prepared electrodes were structurally examined using various characterization analyses, including XRD, FTIR, ICP-OES, and FESEM/EDX. To evaluate the electrochemical performance, galvanostatic charge/discharge measurements were carried out.Results: The results obtained from XRD analysis revealed that the cathodes doped with Zn or Cd possess layered α-NaFeO₂ structure like the one observed for the undoped cathode. Furthermore, the doping process resulted in increment in lattice parameters of a and c, providing more space for insertion/extraction of lithium ions into/from the cathode. According to electrochemical measurements, the samples included with Zn and Cd showed improved discharge capabilities (~ 273.7 and 281.3 mAh/g, respectively) compared to non-doped ones (249.7 mAh/g). Conclusion: Our findings confirm that the controlled doping of cathode with Zn and Cd can effectively stabilize the layered structure and improve electrochemical properties, offering promising design strategies for high-generation lithium-ion batteries.
Introduction and Objectives: As the largest organ exposed to the external environment, the skin is highly susceptible to disruption due to trauma, burns, wounds, surgical interventions, chronic diseases (e.g., diabetes), or inflammatory dermatological reactions. The aim of this study was to fabricate and characterize silk fibroin-lignin nanofiber dressings for the treatment of diabetic wounds.Materials and Methods: Initially, silk fibroin was extracted from silkworm cocoons and nanofibers were fabricated at a voltage of 20 kV using lignin at ratios ranging from 1:5 and 1:6 and 1:7. Subsequently, the nanofibers were immersed in 96% ethanol for 30 minutes to carry out the crosslinking process. In the first step, scanning electron microscopy (SEM) was employed to investigate the morphological features. Then, mechanical, physical, antioxidant, cellular, and antibacterial evaluations were performed to assess the properties of an ideal wound dressing.Results: The results revealed that the composite fibers were uniform in structure across different ratios and possessed nanometer-scale diameters. The swelling rate of the composite samples increased from 359.99 ± 37.53% in pure silk fibroin samples to 468.37 ± 63.47%, indicating favorable stability. Antioxidant and antibacterial assays demonstrated that the addition of lignin enhanced both antioxidant and antibacterial activities. Furthermore, cell viability assessments showed that the presence of lignin did not exert any detrimental effects on the cells, and cell proliferation and growth were observed on the surface of the samples.Conclusion: Since achieving an ideal wound dressing requires critical biological properties, these nanofibers due to their hydroxyl and methoxy phenolic groups in lignin exhibit unique advantages in physical properties, antioxidant activity, antibacterial effects, and cell adhesion. These characteristics make them a promising candidate for biomedical applications, particularly wound healing, and tissue regeneration.
Introduction and Objectives: This study investigated the feasibility of using industrial wastes to produce glass-ceramics suitable for thermal energy storage in concentrated solar power plants. The objective was to produce glass-ceramics from three types of industrial wastes and evaluate their corrosion resistance against molten carbonate salts as the heat transfer medium at high temperatures.Materials and Methods: For this purpose, three raw materials including blast furnace slag, ladle furnace slag, and artificial stone waste were used. The samples were sintered using a single-step method. Phase identification was performed by X-ray diffraction, and microstructure examination was conducted using scanning electron microscopy. Physical properties including density, water absorption, and Vickers hardness were measured, and specific heat capacity was determined by differential scanning calorimetry. Additionally, the samples were exposed to molten carbonate salt at 800°C for one week to evaluate their corrosion resistance.Results: The sample derived from ladle furnace slag, with its dense structure, exhibited the highest hardness (7.9 GPa) and the lowest water absorption (0.028%). The sample derived from blast furnace slag showed the highest specific heat capacity (~ 0.8 J/g·°C). The corrosion test also indicated excellent resistance of the ladle furnace slag-derived sample, with the lowest penetration depth and surface degradation against the molten salt.Conclusion: The glass-ceramic produced from ladle furnace slag, possessing a favourable combination of mechanical properties, physical characteristics, and corrosion resistance, is considered as a suitable and economical option in thermal energy storage systems in contact with molten carbonates.
Introduction and Objectives: Cordierite ceramics (Mg2Al4Si5O18) are recognized as advanced dielectric materials due to their low dielectric constant, very low dielectric loss, high thermal stability, and optimal performance in microwave and millimeter-wave frequency ranges. These materials are utilized in fifth- and sixth-generation (5G and 6G) communication systems. This study investigates the simultaneous substitution effects of Mn⁴⁺ and Ni²⁺ cations for Al³⁺ on the densification, crystalline structure, microstructure, mixing entropy (ΔSmixing), and dielectric properties of cordierite ceramics.Materials and Methods: Samples with different substitution levels (0, 0.25, and 0.50) were prepared by the solid-state synthesis method and subsequently sintered at various temperatures. Phase and microstructural analyses were carried out using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. A network analyzer was employed to measure the dielectric properties at microwave frequencies. In addition, the mixing entropy and lattice distortion were measured, analyzed, and discussed.Results: It was observed that substituting Mn4+ and Ni2+ for Al3+ results in achieving the maximum density at a temperature about 100 °C lower than that of pure cordierite. X-ray diffraction and Raman spectroscopy analyses indicated that a complete solid solution is formed at x=0.25, whereas increasing x to 0.50 results in the appearance of a secondary phase, Mg1.16Mn0.84Si2O6, in addition to the cordierite phase. Microstructural observations also revealed that the average grain size increases with higher substitution levels. The optimal microwave dielectric properties were obtained for Mg2Al3.75(Mn4+Ni4+)0.25Si5O18, with εᵣ= 4.58, Q×f =107333 GHz, and τf = –14.7 ppm/°C, while the value of ΔSmixing was measured to be 2.30 J/mol · K.Conclusion: Controlled substitution of Mn4+ and Ni2+ at an appropriate sintering temperature enables simultaneous optimization of dielectric properties and thermal stability.
Introduction and Objectives: In the present study, a detailed study of the structural and phase changes of the Zirconium-based bulk metallic glasses during annealing process and its effect on the mechanical properties has been conducted.Materials and Methods: In this regard, Zr65Cu15Ti13Ni7 bulk metallic samples with dimensions of 2×30×30 mm3 were prepared using arc melting followed by injection casting in water-cooled copper mold. The heat treatment process has been done for prepared samples at 250-550 oC for 2 h. The resulting structures were examined using field emission scanning electron microscopy, differential thermal analysis, and X-ray diffractometry, and the mechanical behavior was investigated by performing a tensile test using an Instron testing machine. Results: The results showed heat treatment process at a temperature lower than the glass transition temperature can be effective in improving mechanical properties by increasing the number of shear bands. However, heat treatment at higher temperatures leads to the precipitation of CuZr and Cu10Zr7 intermetallic compounds, which greatly affect the mechanical properties and lead to a sharp decrease in tensile strength and elongation. Conclusion: The optimal heat treatment temperature was determined to be 250 °C, which leads to an increase in fracture strength to 1710 MPa and plastic ductility up to 1.65%.
Introduction and Objective: The aim of this research is to investigate the effect of secondary tungsten powder reduction on the physical and mechanical properties of tungsten heavy alloys (WHAs) consolidated by the spark plasma sintering (SPS) method.Materials and Methods: Commercial tungsten powder was reduced at 900 °C for one hour in a hydrogen atmosphere. The type of tungsten oxide was investigated using SEM, EDS, Raman spectroscopy, and XRD analysis. The reduced tungsten powders were pre-sintered in a hydrogen atmosphere at 1150 °C for one hour and finally sintered at 1400 °C using the SPS method (30 MPa, 15 min).Results: The oxygen level of the commercial powder was successfully reduced from 3000 ppm to 770 ppm. SEM and EDS results revealed a uniform microstructure with minimal porosity and oxide dispersion. The hardness and compressive strength were measured to be 340 Vickers and 1611 MPa, respectively.Conclusion: This study confirms that secondary hydrogen reduction of commercial tungsten powder effectively decreases oxygen content and leads to a more homogeneous microstructure with reduced porosity and oxide dispersion. As a result, the spark plasma sintered WHAs exhibited improved hardness and compressive strength.
Introduction and Objectives: Dual-phase steels, particularly DP600, are among the most widely used materials in the automotive industry due to their unique combination of high strength and good formability. Understanding the hot deformation behavior of these steels is crucial for designing optimal hot rolling schedules to produce steel sheets with desired mechanical properties. In this study, an investigation was conducted on the hot deformation behavior of DP600 steel with the aim of determining its critical temperatures.Materials and Methods: In this research, the hot torsion test, one of the most practical methods for simulating industrial hot rolling conditions, was employed to determine the critical temperatures (Tnr, Ar3, and Ar1) of the dual-phase steel by simulating two different rolling schedules, namely average and actual tests.Results: In the average test, the no-recrystallization temperature (Tnr), the starting temperature of austenite-to-ferrite transformation (Ar3), and finishing temperature of ferrite transformation (Ar1) were measured to be 910 °C, 790 °C, and 760 °C, respectively. In contrast, in the actual test, these temperatures were found to be 931 °C, 825 °C, and 765 °C, respectively. Microstructural analyses confirmed the reliability of the obtained results.Conclusion: The results indicated that the values of critical temperatures differ between the two tests due to non-equilibrium conditions. However, the values obtained from the actual test, which closely simulates real rolling conditions, can be effectively used to design an optimal rolling schedule for producing dual-phase steel with the desired tensile strength.
Introduction and Objective: The cobalt-based superalloy FSX-414, owing to its excellent resistance to high-temperature oxidation and hot corrosion, is widely used in the fabrication of first-row stationary vanes in Frame-9 industrial gas turbines. During prolonged service, these critical components are subjected to severe conditions such as thermal fatigue, oxidation, and creep, which can significantly reduce their service life and compromise the reliability of the turbine. The present study focuses on optimizing welding parameters to enhance the durability, mechanical strength, and performance stability of FSX-414 components at elevated temperatures.Materials and Methods: Repair welding was carried out using the Gas Tungsten Arc Welding (GTAW) process with welding currents of 50, 60, and 70 A applied on FSX-414 substrates. Microstructural evaluation revealed that 60 A provided the most favorable weld quality and was therefore selected for further experiments. At this optimized current, four different filler metals—FSX-414, HS25, HS188, and Mar-M918—were employed. Tensile tests were performed following ASTM E8 at room temperature and ASTM E21 at 650°C to evaluate mechanical behavior. Microstructural characterization and fracture analysis were conducted using optical microscopy and scanning electron microscopy.Results: For most welded specimens, failure occurred in the base metal rather than in the weld zone, confirming the adequacy of the welding procedure. However, in the specimen welded with HS188 filler metal, fracture initiated within the weld metal. Detailed analysis showed local segregation of chromium and tungsten in interdendritic regions and the transformation of primary MC carbides into M23C6 carbides, which promoted the formation of brittle phases and facilitated crack initiation.Conclusion: The filler metal Mar-M918 provided the highest tensile strength and toughness at both test temperatures. FSX-414 demonstrated inferior performance, while HS25 and HS188 yielded intermediate results.
Introduction and Objectives: Wear and corrosion are among the primary challenges that reduce the service life and performance of industrial components. In this study, a sol-enhanced method is employed to incorporate ceria into electroless Ni-P/Ni-B coatings to improve mechanical, tribological, and corrosion properties.Materials and Methods: A uniform distribution of ceria nanoparticles was achieved by introducing ceria sol derived from an alkoxide precursor into the Ni-B electroless bath. Characterization was performed by XRD and FE-SEM, DLS, potentiodynamic polarization test, and pin-on-disk wear tests.Results: The results showed that the use of ceria sol improved the uniformity of the distribution of reinforcing particles and formed a relatively dense Ni-B coating with good surface quality and no real surface cracks. The surface features were mainly related to the boundaries of cauliflower nodules. The polarization curve indicates a more stable with slower rate of corrosion for the CeO2-containing coating compared to the substrate, due to the formation of a protective layer and increased surface chemical stability. Using the Ni-P/Ni-B-CeO2 coating on the aluminum substrate resulted in a 21% reduction in the friction coefficient and a 70% reduction in the specific wear rate compared to the substrate.Conclusion: Using sol of ceria in Ni-B coatings, due to the prevention of particle accumulation in the coating, led to a significant increase in corrosion resistance, reduced friction coefficient, and improved wear resistance of the coating.
