فصلنامه مواد پیشرفته در مهندسی
سال چهل و چهارم شماره 2 (تابستان 1404)

Ti-6Al-2Sn-4Zr-2Mo (Ti6242) alloy is a near-alpha titanium alloy widely used in biomedical, automobile, and aviation industries, known for having a high service temperature. The objectives of this study are to compare the electron beam melting and selected laser melting techniques in terms of the microstructure and hardness developed in Ti6242 alloy.

Microstructure and hardness of Ti6242 alloy samples produced by the two-powder bed fusion techniques were analyzed using optical and scanning electron microscopy, X-ray diffractometry, and Vickers hardness test.

The porosity levels in both samples were within the acceptable ranges for powder bed fusion processes. The solidified microstructure of laser powder bed fusion samples consisted of columnar β grains with martensitic α' phase, and that of electron beam powder bed fusion sample consisted of lamellar α+β phases with Widmanstätten and basketweave morphology and α colonies. Williamson-Hall plots revealed higher lattice microstrain in the laser powder bed fusion process. The average hardness values of electron beam powder bed fusion and laser powder bed fusion samples were approximately 408 HV and 401 HV.

Both powder bed fusion techniques employed were capable of producing samples of acceptable porosity levels. The solidified microstructures of the two techniques were somewhat different due to different heating and cooling histories experienced. The electron beam powder bed fusion sample enjoyed smaller lattice microstrain and higher hardness than the laser beam powder bed fusion sample. Hardness of both samples was higher than those of the conventionally fabricated components.

Hydrogels, as three-dimensional hydrophilic scaffolds, play a crucial role in absorbing biological fluids and providing mechanical stability in the tissue regeneration process. This study aims to design and synthesize novel composite hydrogels based on thiol-modified silk fibroin and a zinc-containing bio-metal-organic framework (Zn-Bio MOF) with an adenine ligand to enhance mechanical and biological properties for tissue engineering applications.

Pure silk fibroin was extracted and modified with thiol groups via L-cysteine conjugation. Fourier-transform infrared (FTIR) spectroscopy was conducted to confirm these modifications. The Zn-Bio MOF was synthesized through a hydrothermal process using zinc (II) ions and an adenine ligand. Three types of composite hydrogels were prepared: (1) hydrogel based on thiol-modified silk fibroin, (2) hydrogel based on thiol-modified silk fibroin crosslinked via the Fenton reaction, and (3) composite hydrogel containing Zn-Bio MOF at various concentrations. Material characterization was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD).

FTIR spectroscopy confirmed the reduction in peak intensities at 1650 cm⁻¹ and 3300 cm⁻¹ and the appearance of new peaks corresponding to S-S and S-H bonds. The average particle size of Zn-Bio MOF was 0.39 ± 0.12 nm, with a specific surface area of 1138.3 m²/g. Swelling and degradation analyses indicated that Zn-Bio MOF-containing hydrogels exhibited improved mechanical properties, including higher compressive modulus and toughness, approximately 30% weight loss over 72 hours, and controlled swelling behavior.

The findings of this study suggest that Zn-Bio MOF composite hydrogels, due to their enhanced mechanical properties and controlled swelling behavior, hold significant potential for tissue engineering and biomedical applications.

The properties of coatings deposited by cold spray depend on the parameters of the process. The aim of this research is to investigate the effect of gas pressure and stand-off distance of cold spray process of zinc on a low carbon steel substrate.

In this research, zinc powder was sprayed at pressures of 20 and 30 bar and stand-off distances of 20 and 30 mm. The microstructure of the coatings was investigated using optical and scanning electron microscope and the micro-hardness of the coatings was measured. Then, the selected coating and steel substrate were subjected to polarization corrosion test.

The results showed that increasing the gas pressure from 20 to 30 bar decreased the porosity and increased the micro-hardness due to further deformation. Also, for a constant pressure, the stand-off distance of 20 mm has the lowest porosity and the highest micro-hardness due to the higher temperature of the particles when impact the substrate. The results obtained from the polarization test show that the coating has a sacrificial nature compared to the substrate and reduces the corrosion current density by 48% and corrosion rate by 33% compared to the substrate.

In this study, the effect of gas pressure and stand-off distance of cold spray process of zinc on low carbon steel substrate was investigated. The results showed that increasing the gas pressure from 20 to 30 bar and reducing the stand-off distance from 30 to 20 mm improved porosity and increased coatings micro-hardness. The results of this study can be used to optimize the parameters of the cold spraying of zinc for use in various industries such as automotive, power plants and marine infrastructure.

In this research, the laser drilling process was carried out by a single pulse method and the effect of displacement and focal length parameters on the geometry of the hole (Inlet diameter, Outlet diameter, Taper, and Entrance circularity error) was studied.

In this study, statistical-experimental modeling was done using a full factorial experiment design with two factors of displacement and focal length in ten and seven levels on Hastelloy-X superalloy, respectively. Also, four cases of inlet and outlet hole diameter, cone angle, and circularity of the inlet diameter were considered as responses to the design of the experiment.

The results showed that the diameter of the inlet and outlet holes increased with the increase of displacement and positive changes in the focal length. Also, the variation of the hole diameter was quite acceptable from 183 μm to 1768 μm with the single pulse method on the Hastelloy-X sheet with a thickness of 1 mm.

The optimized results of the answers revealed that the maximum value of the hole inlet diameter was 997.848 μm, the maximum hole outlet diameter was 771.341 μm, the taper was 6.492 degrees, and finally the entrance circularity error was 0.0167.

Positron Annihilation Lifetime Spectroscopy is a sensitive method for investigating the free volume in polymers at the atomic scale, enabling the determination of pore size, shape, and concentration. It is widely used as a complementary identification tool alongside other macroscopic experimental techniques. In this study, for the first time, PALS was employed to examine the free volume in epoxy/graphene oxide nanocomposites and its correlation with the tensile behavior of the samples.

In this research, Epoxy-based samples containing different weight percentages of graphene oxide (0.1, 0.3, 0.5, and 0.7 wt.%) were analyzed using PALS. A Na22 radioisotope with an activity of ~5 µCi was used as the positron source, and fast plastic scintillation detectors with a time resolution of 225 picoseconds were employed. Uniaxial tensile tests were also conducted.

The results showed that the lowest free pore volume (i.e. 83.87 A3) was related to the sample containing 0.3 wt.% graphene oxide, indicating a decrease of ~ 8% in the free pore volume in this sample compared to the pure epoxy one (i.e. 90.97 A3). The best tensile behavior was obtained for the sample containing 0.3 wt. % graphene oxide (i.e. 51.1 MPa), which revealed an 18 % increase in the tensile strength compared to the pure epoxy sample (i.e. 43.3 MPa).

In general, the results of the positron annihilation lifetime spectroscopy and tensile strength measurements of the epoxy/graphene oxide nanocomposites showed that there was an inverse relationship between the free pore volume and tensile strength.

This study aims to enhance the optical properties of polycrystalline alumina by controlling grain growth and minimizing structural defects. To achieve this, the influence of amorphous silicon nitride (Si₃N₄) nanoparticles as a reinforcing agent, in conjunction with MgO and La₂O₃ as sintering aids, on the infrared transmittance of PA was investigated. Furthermore, the role of the dispersing agent in improving slurry homogeneity and particle distribution was evaluated.

The composite materials were synthesized via a chemical precipitation process, wherein alumina powder was mixed with Si3N4 nanoparticles, magnesium nitrate, lanthanum nitrate, and a dispersing agent in an aqueous solution.Ultrasonic waves were employed to enhance particle dispersion, and the slurry pH was adjusted to 10 to stabilize the suspension.Subsequent to powder preparation, spark plasma sintering was utilized to achieve densification and control grain growth. The microstructural and optical characteristics of the samples were then analyzed using X-ray diffraction, field emission scanning electron microscopy and infrared spectroscopy.

The findings indicated that the incorporation of Si3N4 nanoparticles (0.1 wt%) and a dispersing agent (2 wt%) led to an enhancement in infrared transmittance, with a maximum achieved of 85% within the 5–6 µm wavelength range. This observation was corroborated by microscopic analysis, which confirmed a reduction in grain size and an improvement in microstructural uniformity. Furthermore, X-ray diffraction analysis substantiated the preservation of the crystalline structure of alumina across all samples.

The optimization of the sintering process, in conjunction with the incorporation of silicon nitride nanoparticles, facilitates the fabrication of transparent alumina, which exhibits augmented optical properties. These materials hold considerable promise for applications in infrared-sensitive systems, including missile guidance and optical sensor technologies.

Acidic solutions are widely used for acid pickling, removing impurities and contaminants from the surfaces of metal objects in various industries. This process, however, reduces the corrosion resistance of metal. The objective of this study is to assess the application of certain cost-effective pharmaceuticals as eco-friendly corrosion inhibitors to mitigate metal corrosion in acidic environments.

The adsorption quality and the potential for forming a stable protective layer of paracetamol on the (110) plane of iron have been investigated and analyzed using first-principles calculations based on density functional theory.

Given the presence of a benzene ring and hydroxyl and amide functional groups in paracetamol's structure, numerous structural arrangements were created and optimized. Among these, the arrangement where the paracetamol molecule was adsorbed onto the (110) plane via the benzene ring proved to be the most stable, with an adsorption energy of -242 kJ/mol. The sign and magnitude of the calculated adsorption energy suggest that paracetamol is a suitable corrosion inhibitor for iron surface. The projected density of states, charge density difference, Bader charge analysis, and electron localization function for the optimal adsorption state were calculated to evaluate the molecule-surface interaction. 

These analyses revealed that the hybridization of the d orbitals of the metal atoms and the π orbitals of the benzene ring, forming a back-donation π bond, played a major role in the adsorption of the paracetamol molecule on the iron surface.

Nickel nanoparticles are utilized in electronic printing, multilayer ceramic capacitors, magnetic devices, and supercapacitor electrodes in the electronics industry due to their favorable physical, chemical, and magnetic properties, low cost, and optimal sintering temperature. The objective of this study is to synthesize nickel nanoparticles via laser ablation in liquid.

To characterize the synthesized nanoparticles, field-emission scanning electron microscopy, dynamic light scattering, X-ray diffraction, and ultraviolet-visible spectroscopy were employed.

The results revealed that nanoparticles synthesized in distilled water consisted of nickel nanoparticles with FCC crystalline structure and a nickel/nickel oxide (Ni/NiO) core-shell structure. These particles exhibited an average size of 70 nm, spherical morphology, and a rough surface. In contrast, nanoparticles synthesized in a solvent containing Polyvinylpyrrolidone as a stabilizer comprised pure nickel nanoparticles with an average size of 60 nm, spherical morphology, and an FCC crystalline structure. The Polyvinylpyrrolidone-stabilized nanoparticles, owing to their uniform morphology, narrow particle size distribution, and absence of oxide formation, are a promising candidate for nickel nanoparticle synthesis.

The nickel nanoparticles synthesized in the Polyvinylpyrrolidone-containing solvent, due to their optimal morphology, uniform particle size distribution, and lack of oxide formation, are well-suited for the production of conductive inks.