مجله مواد و فناوری های پیشرفته
سال دهم شماره 2 (تابستان 1400)

IN718 alloy is a high strength Nickel base superalloy that mainly used in moderate temperatures and corrosive service conditions. In the present study, samples produced by selective laser melting (SLM) at 1040 °C for 120 minutes were prepared under solution treatment. After solution, the samples were cooled in three cooling media of water, air and extinguished furnace with open door. Finally, the samples were aged in three standard conditions for 48 and 72 hours. To investigate the effect of cooling rate after solution and aging time on precipitates characteristics and microstructure of samples, Field Emission Scanning Electron Microscope (FESEM), X-ray diffraction (XRD) and hardness test were used. The results showed that increasing the aging time under constant solution conditions increases the volume fraction and the size of the secondary phases. Also, reducing the cooling rate in the solution step leads to increasing the hardness of the samples in the aging stage. Finally, with increasing aging time, the maximum hardness of the sample was 794H. v.

In this research, pure Yttrium Aluminum Garnet (YAG, Y3Al5O12) nanostructures were synthesized through a two-step process by using chloride precursors in a solution of water–ethanol electrolyte with specific ratio. Also, the effect of cationic surfactant CTAB, on the size and the morphology of the prepared nanostructures were investigated. For the synthesis of YAG, a layer of hydroxide film was deposited on the surface of cathode via cathodic electrodeposition method and then, it was transformed to the final oxide product in the course of a thermal operation. X-Ray Diffraction (XRD) analysis was used for characterization of phase and crystal structure of prepared materials and also Fourier Transform Infra-Red spectroscopy (FTIR) was used for characterization of absorption bonds. Thermal behavior of deposited hydroxide during the thermal operation was studied by Differential Thermal Analysis and Thermal Gravimetric Analysis (DTA-TGA) technique. The morphology and particle size of obtained powder was determined by Scanning Electron Microscopy (SEM). The results of our studies showed that the cathodic electrodeposition method is a practical and very efficient method for preparation of YAG nanostructures and addition of a cationic surfactant like CTAB into the electrolyte during the electrochemical deposition can lead to the formation of smaller particles and also has an impressive effect on the homogeneity and narrower particles size distribution.

The presence of macropores in the scaffolds, in addition to increasing the rate of adsorption, provides a structure for the growth of osteoblasts and promote the formation of new bone with a complete and uniform structure. In this study, calcium phosphate powder was prepared by mixing tetra calcium phosphate and dicalcium phosphate dihydrated. To achieve stable suspension cement powder was mixed with deionized water at powder to liquid ratio of 0.5 g/mL and 3 wt % of dispersant factor, dolapix, and 4 wt % of polyvinyl alcohol were added to suspension. Scaffolds were prepared by freeze-casting method. The average particle size of cement powder was estimated to be 5.45 μm. SEM micrographs indicate that created pores in the structure are in the range of 100-300 μm. Nanostructure apatite is formed on the wall of pores after soaking in SBF. Compressive strength of samples was measured between 1.2 to 2.2 MPa. Cell numbers on the surface of the samples are tripled over time.

In this study, the effect of substrate surface preparation on the polypyrrole/polyaniline conductive polymers coating process and corrosion resistance in the presence of coating has been investigated. The preparation of the 304 stainless steel substarate was done by electropolishing, manual grinding, and sandblasting. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and roughness tester have been used to investigate the surface morphology. The coating process for polypyrrole/polyaniline conductive polymers were carried out over a period of 900 seconds with potentiostat technique at a voltage of +900 mV. Based on pull-off test results, the most adherent coating belonged to manual grinded sample with 0.67 MPa tensile stress. According to the results of electrochemical impedance test and polarization of potentiodynamics after one hour immersion in a solution of 3.5 wt % sodium chloride, the substrate prepared by manual grinding had the highest polarization resistance of 18428 Ω.cm2, the least corrosion current density of 1.76 × 10-7 A/cm2, and the highest potential of -0.080 V vs. SCE.

This study was conducted to investigate the effect of adding titanium diboride (TiB2) nanoparticles on the microstructure and tensile properties of the Al5083 matrix composite. Al5083/TiB2 metal matrix composites (with 5 and 10 wt % reinforcement) along with zirconium (Zr) and cerium oxide (CeO2) additives with different wt % were fabricated by in situ-stir casting at 1000 °C. The samples were then subjected to hot extrusion for uniform distribution of reinforcements in the matrix. TiB2 nanoparticles were in-situ processed in molten aluminum using the precursors such as cryolite (Na3AlF6), titanium oxide (TiO2), and potassium tetrafluoroborate (KBF4). The microstructure, surfaces, and failure mechanism of the samples were investigated using X-ray diffraction (XRD), optical microscopy (OM), and scanning electron microscopy (SEM). Tensile test results showed that the addition of 10 wt % TiB2 particles increased the ultimate tensile strength by 17.7 % and decreased the strain by 19.2 % compared to the sample without reinforcement. Besides, the addition of Zr and CeO2 increased the strength by 35.8 % and the strain of the sample containing 78 % by 10 % reinforcement compared to the sample without reinforcement due to the removal of intermetallic compound Al3Ti and the incompatibility between coefficients of thermal expansion (CTE) with the matrix. Also, post-extrusion annealing in the sample with 10 wt % TiB2 reduced the tensile strength.

Modern system-on-chip (SoC) designers are trying to include more considerations in designing building blocks to present reliable integrated digital circuits as well as high-density, high-speed, and low-power ones. In this paper, an innovative device so-called High Electron Mobility Field-Effect Diode (HEMFED) is successfully designed based on AlGaN/GaN. To prohibit leakage of GaN buffer layer and weaken the impact of the buffer traps on electrical transport properties of two-dimensional electron gas (2-DEG), AlN spacer layer is embedded in the heterostructure. The proposed structure enhances ION/IOFF ratio up to 4.88×107 times compared to the AlGaN/GaN High Electron Mobility Field-Effect Transistor (HEMT) counterpart, 8.20×108 times compared to the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) counterpart, and 9.05×104 times compared to the Si Field-Effect Diode (FED) counterpart, at a supply voltage of VDD=1.8 V. This superiority of the proposed device is referred to the formation of a strong electric field of 800 kV/cm in 2-DEEG and the precipitation of electron sheet carriers in the channel. Accordingly, the proposed device can be utilized in high-speed and low-power digital applications.

Tellurium dioxide (TeO2) is an important semiconductor, which it has high acousto-optic figure of merit, chemical stability and mechanical durability and both in its crystalline and amorphous forms, making it suitable for theoretical studies and technological applications such as optical devices, γ-ray detectors, and gas sensors. In this work, the TeO2 thin film with three different thicknesses was prepared by vacuum thermal evaporation method. The effect of gamma irradiation in the range of 10-40 Gy and also the effect of thermal annealing on properties of TeO2 thin films were investigated. Scanning Electron Microscopy (SEM) results showed the formation of the film with smooth surface. X-Ray Diffraction (XRD) analysis were revealed that the as-deposited films were amorphous but after annealing at 400 °C, the crystalline phase of the samples occurred. The optical absorbance after annealing and gamma radiation was increased but the band gap  decreased. The electrical current of samples was increased with increasing of films thickness, gamma dose and also after annealing.

Stellite-6 alloy was deposited on a SS316 stainless steel substrate by Electro-Spark Deposition; subsequently, the thickness of deposition layer was around 100 ± 10 micron. High Energy Shot Peening process was applied to improve coated layer properties. Microstructure, chemical composition, micro hardness variation in cross sections, wear properties and visual check for discontinuities of coated layer were studied by employing Field Emission Scanning Electron Microscopy, Optical Microscopy, EDS line scan and pin on disk wear test, before and after the high energy shot peening process. The results show decreasing the surface roughness from 14 to 4.5 micron and improving the micro-hardness of coated layer from 450 to 540 HVN due to High Energy Shot Peening process on the Electro-Spark Deposition coated layers. On the other hand, the wear properties of the coating are improved, the number of defects such as porosities is reduced, and micro-cracks and defects in melts are healed due to compressive residual stress and severe wax deformation.